diff --git "a/lib/python3.11/site-packages/mpmath/function_docs.py" "b/lib/python3.11/site-packages/mpmath/function_docs.py" new file mode 100644--- /dev/null +++ "b/lib/python3.11/site-packages/mpmath/function_docs.py" @@ -0,0 +1,10201 @@ +""" +Extended docstrings for functions.py +""" + + +pi = r""" +`\pi`, roughly equal to 3.141592654, represents the area of the unit +circle, the half-period of trigonometric functions, and many other +things in mathematics. + +Mpmath can evaluate `\pi` to arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +pi + 3.1415926535897932384626433832795028841971693993751 + +This shows digits 99991-100000 of `\pi` (the last digit is actually +a 4 when the decimal expansion is truncated, but here the nearest +rounding is used):: + + >>> mp.dps = 100000 + >>> str(pi)[-10:] + '5549362465' + +**Possible issues** + +:data:`pi` always rounds to the nearest floating-point +number when used. This means that exact mathematical identities +involving `\pi` will generally not be preserved in floating-point +arithmetic. In particular, multiples of :data:`pi` (except for +the trivial case ``0*pi``) are *not* the exact roots of +:func:`~mpmath.sin`, but differ roughly by the current epsilon:: + + >>> mp.dps = 15 + >>> sin(pi) + 1.22464679914735e-16 + +One solution is to use the :func:`~mpmath.sinpi` function instead:: + + >>> sinpi(1) + 0.0 + +See the documentation of trigonometric functions for additional +details. + +**References** + +* [BorweinBorwein]_ + +""" + +degree = r""" +Represents one degree of angle, `1^{\circ} = \pi/180`, or +about 0.01745329. This constant may be evaluated to arbitrary +precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +degree + 0.017453292519943295769236907684886127134428718885417 + +The :data:`degree` object is convenient for conversion +to radians:: + + >>> sin(30 * degree) + 0.5 + >>> asin(0.5) / degree + 30.0 +""" + +e = r""" +The transcendental number `e` = 2.718281828... is the base of the +natural logarithm (:func:`~mpmath.ln`) and of the exponential function +(:func:`~mpmath.exp`). + +Mpmath can be evaluate `e` to arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +e + 2.7182818284590452353602874713526624977572470937 + +This shows digits 99991-100000 of `e` (the last digit is actually +a 5 when the decimal expansion is truncated, but here the nearest +rounding is used):: + + >>> mp.dps = 100000 + >>> str(e)[-10:] + '2100427166' + +**Possible issues** + +:data:`e` always rounds to the nearest floating-point number +when used, and mathematical identities involving `e` may not +hold in floating-point arithmetic. For example, ``ln(e)`` +might not evaluate exactly to 1. + +In particular, don't use ``e**x`` to compute the exponential +function. Use ``exp(x)`` instead; this is both faster and more +accurate. +""" + +phi = r""" +Represents the golden ratio `\phi = (1+\sqrt 5)/2`, +approximately equal to 1.6180339887. To high precision, +its value is:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +phi + 1.6180339887498948482045868343656381177203091798058 + +Formulas for the golden ratio include the following:: + + >>> (1+sqrt(5))/2 + 1.6180339887498948482045868343656381177203091798058 + >>> findroot(lambda x: x**2-x-1, 1) + 1.6180339887498948482045868343656381177203091798058 + >>> limit(lambda n: fib(n+1)/fib(n), inf) + 1.6180339887498948482045868343656381177203091798058 +""" + +euler = r""" +Euler's constant or the Euler-Mascheroni constant `\gamma` += 0.57721566... is a number of central importance to +number theory and special functions. It is defined as the limit + +.. math :: + + \gamma = \lim_{n\to\infty} H_n - \log n + +where `H_n = 1 + \frac{1}{2} + \ldots + \frac{1}{n}` is a harmonic +number (see :func:`~mpmath.harmonic`). + +Evaluation of `\gamma` is supported at arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +euler + 0.57721566490153286060651209008240243104215933593992 + +We can also compute `\gamma` directly from the definition, +although this is less efficient:: + + >>> limit(lambda n: harmonic(n)-log(n), inf) + 0.57721566490153286060651209008240243104215933593992 + +This shows digits 9991-10000 of `\gamma` (the last digit is actually +a 5 when the decimal expansion is truncated, but here the nearest +rounding is used):: + + >>> mp.dps = 10000 + >>> str(euler)[-10:] + '4679858166' + +Integrals, series, and representations for `\gamma` in terms of +special functions include the following (there are many others):: + + >>> mp.dps = 25 + >>> -quad(lambda x: exp(-x)*log(x), [0,inf]) + 0.5772156649015328606065121 + >>> quad(lambda x,y: (x-1)/(1-x*y)/log(x*y), [0,1], [0,1]) + 0.5772156649015328606065121 + >>> nsum(lambda k: 1/k-log(1+1/k), [1,inf]) + 0.5772156649015328606065121 + >>> nsum(lambda k: (-1)**k*zeta(k)/k, [2,inf]) + 0.5772156649015328606065121 + >>> -diff(gamma, 1) + 0.5772156649015328606065121 + >>> limit(lambda x: 1/x-gamma(x), 0) + 0.5772156649015328606065121 + >>> limit(lambda x: zeta(x)-1/(x-1), 1) + 0.5772156649015328606065121 + >>> (log(2*pi*nprod(lambda n: + ... exp(-2+2/n)*(1+2/n)**n, [1,inf]))-3)/2 + 0.5772156649015328606065121 + +For generalizations of the identities `\gamma = -\Gamma'(1)` +and `\gamma = \lim_{x\to1} \zeta(x)-1/(x-1)`, see +:func:`~mpmath.psi` and :func:`~mpmath.stieltjes` respectively. + +**References** + +* [BorweinBailey]_ + +""" + +catalan = r""" +Catalan's constant `K` = 0.91596559... is given by the infinite +series + +.. math :: + + K = \sum_{k=0}^{\infty} \frac{(-1)^k}{(2k+1)^2}. + +Mpmath can evaluate it to arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +catalan + 0.91596559417721901505460351493238411077414937428167 + +One can also compute `K` directly from the definition, although +this is significantly less efficient:: + + >>> nsum(lambda k: (-1)**k/(2*k+1)**2, [0, inf]) + 0.91596559417721901505460351493238411077414937428167 + +This shows digits 9991-10000 of `K` (the last digit is actually +a 3 when the decimal expansion is truncated, but here the nearest +rounding is used):: + + >>> mp.dps = 10000 + >>> str(catalan)[-10:] + '9537871504' + +Catalan's constant has numerous integral representations:: + + >>> mp.dps = 50 + >>> quad(lambda x: -log(x)/(1+x**2), [0, 1]) + 0.91596559417721901505460351493238411077414937428167 + >>> quad(lambda x: atan(x)/x, [0, 1]) + 0.91596559417721901505460351493238411077414937428167 + >>> quad(lambda x: ellipk(x**2)/2, [0, 1]) + 0.91596559417721901505460351493238411077414937428167 + >>> quad(lambda x,y: 1/(1+(x*y)**2), [0, 1], [0, 1]) + 0.91596559417721901505460351493238411077414937428167 + +As well as series representations:: + + >>> pi*log(sqrt(3)+2)/8 + 3*nsum(lambda n: + ... (fac(n)/(2*n+1))**2/fac(2*n), [0, inf])/8 + 0.91596559417721901505460351493238411077414937428167 + >>> 1-nsum(lambda n: n*zeta(2*n+1)/16**n, [1,inf]) + 0.91596559417721901505460351493238411077414937428167 +""" + +khinchin = r""" +Khinchin's constant `K` = 2.68542... is a number that +appears in the theory of continued fractions. Mpmath can evaluate +it to arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +khinchin + 2.6854520010653064453097148354817956938203822939945 + +An integral representation is:: + + >>> I = quad(lambda x: log((1-x**2)/sincpi(x))/x/(1+x), [0, 1]) + >>> 2*exp(1/log(2)*I) + 2.6854520010653064453097148354817956938203822939945 + +The computation of ``khinchin`` is based on an efficient +implementation of the following series:: + + >>> f = lambda n: (zeta(2*n)-1)/n*sum((-1)**(k+1)/mpf(k) + ... for k in range(1,2*int(n))) + >>> exp(nsum(f, [1,inf])/log(2)) + 2.6854520010653064453097148354817956938203822939945 +""" + +glaisher = r""" +Glaisher's constant `A`, also known as the Glaisher-Kinkelin +constant, is a number approximately equal to 1.282427129 that +sometimes appears in formulas related to gamma and zeta functions. +It is also related to the Barnes G-function (see :func:`~mpmath.barnesg`). + +The constant is defined as `A = \exp(1/12-\zeta'(-1))` where +`\zeta'(s)` denotes the derivative of the Riemann zeta function +(see :func:`~mpmath.zeta`). + +Mpmath can evaluate Glaisher's constant to arbitrary precision: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +glaisher + 1.282427129100622636875342568869791727767688927325 + +We can verify that the value computed by :data:`glaisher` is +correct using mpmath's facilities for numerical +differentiation and arbitrary evaluation of the zeta function: + + >>> exp(mpf(1)/12 - diff(zeta, -1)) + 1.282427129100622636875342568869791727767688927325 + +Here is an example of an integral that can be evaluated in +terms of Glaisher's constant: + + >>> mp.dps = 15 + >>> quad(lambda x: log(gamma(x)), [1, 1.5]) + -0.0428537406502909 + >>> -0.5 - 7*log(2)/24 + log(pi)/4 + 3*log(glaisher)/2 + -0.042853740650291 + +Mpmath computes Glaisher's constant by applying Euler-Maclaurin +summation to a slowly convergent series. The implementation is +reasonably efficient up to about 10,000 digits. See the source +code for additional details. + +References: +http://mathworld.wolfram.com/Glaisher-KinkelinConstant.html +""" + +apery = r""" +Represents Apery's constant, which is the irrational number +approximately equal to 1.2020569 given by + +.. math :: + + \zeta(3) = \sum_{k=1}^\infty\frac{1}{k^3}. + +The calculation is based on an efficient hypergeometric +series. To 50 decimal places, the value is given by:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +apery + 1.2020569031595942853997381615114499907649862923405 + +Other ways to evaluate Apery's constant using mpmath +include:: + + >>> zeta(3) + 1.2020569031595942853997381615114499907649862923405 + >>> -psi(2,1)/2 + 1.2020569031595942853997381615114499907649862923405 + >>> 8*nsum(lambda k: 1/(2*k+1)**3, [0,inf])/7 + 1.2020569031595942853997381615114499907649862923405 + >>> f = lambda k: 2/k**3/(exp(2*pi*k)-1) + >>> 7*pi**3/180 - nsum(f, [1,inf]) + 1.2020569031595942853997381615114499907649862923405 + +This shows digits 9991-10000 of Apery's constant:: + + >>> mp.dps = 10000 + >>> str(apery)[-10:] + '3189504235' +""" + +mertens = r""" +Represents the Mertens or Meissel-Mertens constant, which is the +prime number analog of Euler's constant: + +.. math :: + + B_1 = \lim_{N\to\infty} + \left(\sum_{p_k \le N} \frac{1}{p_k} - \log \log N \right) + +Here `p_k` denotes the `k`-th prime number. Other names for this +constant include the Hadamard-de la Vallee-Poussin constant or +the prime reciprocal constant. + +The following gives the Mertens constant to 50 digits:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +mertens + 0.2614972128476427837554268386086958590515666482612 + +References: +http://mathworld.wolfram.com/MertensConstant.html +""" + +twinprime = r""" +Represents the twin prime constant, which is the factor `C_2` +featuring in the Hardy-Littlewood conjecture for the growth of the +twin prime counting function, + +.. math :: + + \pi_2(n) \sim 2 C_2 \frac{n}{\log^2 n}. + +It is given by the product over primes + +.. math :: + + C_2 = \prod_{p\ge3} \frac{p(p-2)}{(p-1)^2} \approx 0.66016 + +Computing `C_2` to 50 digits:: + + >>> from mpmath import * + >>> mp.dps = 50; mp.pretty = True + >>> +twinprime + 0.66016181584686957392781211001455577843262336028473 + +References: +http://mathworld.wolfram.com/TwinPrimesConstant.html +""" + +ln = r""" +Computes the natural logarithm of `x`, `\ln x`. +See :func:`~mpmath.log` for additional documentation.""" + +sqrt = r""" +``sqrt(x)`` gives the principal square root of `x`, `\sqrt x`. +For positive real numbers, the principal root is simply the +positive square root. For arbitrary complex numbers, the principal +square root is defined to satisfy `\sqrt x = \exp(\log(x)/2)`. +The function thus has a branch cut along the negative half real axis. + +For all mpmath numbers ``x``, calling ``sqrt(x)`` is equivalent to +performing ``x**0.5``. + +**Examples** + +Basic examples and limits:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> sqrt(10) + 3.16227766016838 + >>> sqrt(100) + 10.0 + >>> sqrt(-4) + (0.0 + 2.0j) + >>> sqrt(1+1j) + (1.09868411346781 + 0.455089860562227j) + >>> sqrt(inf) + +inf + +Square root evaluation is fast at huge precision:: + + >>> mp.dps = 50000 + >>> a = sqrt(3) + >>> str(a)[-10:] + '9329332815' + +:func:`mpmath.iv.sqrt` supports interval arguments:: + + >>> iv.dps = 15; iv.pretty = True + >>> iv.sqrt([16,100]) + [4.0, 10.0] + >>> iv.sqrt(2) + [1.4142135623730949234, 1.4142135623730951455] + >>> iv.sqrt(2) ** 2 + [1.9999999999999995559, 2.0000000000000004441] + +""" + +cbrt = r""" +``cbrt(x)`` computes the cube root of `x`, `x^{1/3}`. This +function is faster and more accurate than raising to a floating-point +fraction:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> 125**(mpf(1)/3) + mpf('4.9999999999999991') + >>> cbrt(125) + mpf('5.0') + +Every nonzero complex number has three cube roots. This function +returns the cube root defined by `\exp(\log(x)/3)` where the +principal branch of the natural logarithm is used. Note that this +does not give a real cube root for negative real numbers:: + + >>> mp.pretty = True + >>> cbrt(-1) + (0.5 + 0.866025403784439j) +""" + +exp = r""" +Computes the exponential function, + +.. math :: + + \exp(x) = e^x = \sum_{k=0}^{\infty} \frac{x^k}{k!}. + +For complex numbers, the exponential function also satisfies + +.. math :: + + \exp(x+yi) = e^x (\cos y + i \sin y). + +**Basic examples** + +Some values of the exponential function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> exp(0) + 1.0 + >>> exp(1) + 2.718281828459045235360287 + >>> exp(-1) + 0.3678794411714423215955238 + >>> exp(inf) + +inf + >>> exp(-inf) + 0.0 + +Arguments can be arbitrarily large:: + + >>> exp(10000) + 8.806818225662921587261496e+4342 + >>> exp(-10000) + 1.135483865314736098540939e-4343 + +Evaluation is supported for interval arguments via +:func:`mpmath.iv.exp`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.exp([-inf,0]) + [0.0, 1.0] + >>> iv.exp([0,1]) + [1.0, 2.71828182845904523536028749558] + +The exponential function can be evaluated efficiently to arbitrary +precision:: + + >>> mp.dps = 10000 + >>> exp(pi) #doctest: +ELLIPSIS + 23.140692632779269005729...8984304016040616 + +**Functional properties** + +Numerical verification of Euler's identity for the complex +exponential function:: + + >>> mp.dps = 15 + >>> exp(j*pi)+1 + (0.0 + 1.22464679914735e-16j) + >>> chop(exp(j*pi)+1) + 0.0 + +This recovers the coefficients (reciprocal factorials) in the +Maclaurin series expansion of exp:: + + >>> nprint(taylor(exp, 0, 5)) + [1.0, 1.0, 0.5, 0.166667, 0.0416667, 0.00833333] + +The exponential function is its own derivative and antiderivative:: + + >>> exp(pi) + 23.1406926327793 + >>> diff(exp, pi) + 23.1406926327793 + >>> quad(exp, [-inf, pi]) + 23.1406926327793 + +The exponential function can be evaluated using various methods, +including direct summation of the series, limits, and solving +the defining differential equation:: + + >>> nsum(lambda k: pi**k/fac(k), [0,inf]) + 23.1406926327793 + >>> limit(lambda k: (1+pi/k)**k, inf) + 23.1406926327793 + >>> odefun(lambda t, x: x, 0, 1)(pi) + 23.1406926327793 +""" + +cosh = r""" +Computes the hyperbolic cosine of `x`, +`\cosh(x) = (e^x + e^{-x})/2`. Values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> cosh(0) + 1.0 + >>> cosh(1) + 1.543080634815243778477906 + >>> cosh(-inf), cosh(+inf) + (+inf, +inf) + +The hyperbolic cosine is an even, convex function with +a global minimum at `x = 0`, having a Maclaurin series +that starts:: + + >>> nprint(chop(taylor(cosh, 0, 5))) + [1.0, 0.0, 0.5, 0.0, 0.0416667, 0.0] + +Generalized to complex numbers, the hyperbolic cosine is +equivalent to a cosine with the argument rotated +in the imaginary direction, or `\cosh x = \cos ix`:: + + >>> cosh(2+3j) + (-3.724545504915322565473971 + 0.5118225699873846088344638j) + >>> cos(3-2j) + (-3.724545504915322565473971 + 0.5118225699873846088344638j) +""" + +sinh = r""" +Computes the hyperbolic sine of `x`, +`\sinh(x) = (e^x - e^{-x})/2`. Values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> sinh(0) + 0.0 + >>> sinh(1) + 1.175201193643801456882382 + >>> sinh(-inf), sinh(+inf) + (-inf, +inf) + +The hyperbolic sine is an odd function, with a Maclaurin +series that starts:: + + >>> nprint(chop(taylor(sinh, 0, 5))) + [0.0, 1.0, 0.0, 0.166667, 0.0, 0.00833333] + +Generalized to complex numbers, the hyperbolic sine is +essentially a sine with a rotation `i` applied to +the argument; more precisely, `\sinh x = -i \sin ix`:: + + >>> sinh(2+3j) + (-3.590564589985779952012565 + 0.5309210862485198052670401j) + >>> j*sin(3-2j) + (-3.590564589985779952012565 + 0.5309210862485198052670401j) +""" + +tanh = r""" +Computes the hyperbolic tangent of `x`, +`\tanh(x) = \sinh(x)/\cosh(x)`. Values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> tanh(0) + 0.0 + >>> tanh(1) + 0.7615941559557648881194583 + >>> tanh(-inf), tanh(inf) + (-1.0, 1.0) + +The hyperbolic tangent is an odd, sigmoidal function, similar +to the inverse tangent and error function. Its Maclaurin +series is:: + + >>> nprint(chop(taylor(tanh, 0, 5))) + [0.0, 1.0, 0.0, -0.333333, 0.0, 0.133333] + +Generalized to complex numbers, the hyperbolic tangent is +essentially a tangent with a rotation `i` applied to +the argument; more precisely, `\tanh x = -i \tan ix`:: + + >>> tanh(2+3j) + (0.9653858790221331242784803 - 0.009884375038322493720314034j) + >>> j*tan(3-2j) + (0.9653858790221331242784803 - 0.009884375038322493720314034j) +""" + +cos = r""" +Computes the cosine of `x`, `\cos(x)`. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> cos(pi/3) + 0.5 + >>> cos(100000001) + -0.9802850113244713353133243 + >>> cos(2+3j) + (-4.189625690968807230132555 - 9.109227893755336597979197j) + >>> cos(inf) + nan + >>> nprint(chop(taylor(cos, 0, 6))) + [1.0, 0.0, -0.5, 0.0, 0.0416667, 0.0, -0.00138889] + +Intervals are supported via :func:`mpmath.iv.cos`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.cos([0,1]) + [0.540302305868139717400936602301, 1.0] + >>> iv.cos([0,2]) + [-0.41614683654714238699756823214, 1.0] +""" + +sin = r""" +Computes the sine of `x`, `\sin(x)`. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> sin(pi/3) + 0.8660254037844386467637232 + >>> sin(100000001) + 0.1975887055794968911438743 + >>> sin(2+3j) + (9.1544991469114295734673 - 4.168906959966564350754813j) + >>> sin(inf) + nan + >>> nprint(chop(taylor(sin, 0, 6))) + [0.0, 1.0, 0.0, -0.166667, 0.0, 0.00833333, 0.0] + +Intervals are supported via :func:`mpmath.iv.sin`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.sin([0,1]) + [0.0, 0.841470984807896506652502331201] + >>> iv.sin([0,2]) + [0.0, 1.0] +""" + +tan = r""" +Computes the tangent of `x`, `\tan(x) = \frac{\sin(x)}{\cos(x)}`. +The tangent function is singular at `x = (n+1/2)\pi`, but +``tan(x)`` always returns a finite result since `(n+1/2)\pi` +cannot be represented exactly using floating-point arithmetic. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> tan(pi/3) + 1.732050807568877293527446 + >>> tan(100000001) + -0.2015625081449864533091058 + >>> tan(2+3j) + (-0.003764025641504248292751221 + 1.003238627353609801446359j) + >>> tan(inf) + nan + >>> nprint(chop(taylor(tan, 0, 6))) + [0.0, 1.0, 0.0, 0.333333, 0.0, 0.133333, 0.0] + +Intervals are supported via :func:`mpmath.iv.tan`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.tan([0,1]) + [0.0, 1.55740772465490223050697482944] + >>> iv.tan([0,2]) # Interval includes a singularity + [-inf, +inf] +""" + +sec = r""" +Computes the secant of `x`, `\mathrm{sec}(x) = \frac{1}{\cos(x)}`. +The secant function is singular at `x = (n+1/2)\pi`, but +``sec(x)`` always returns a finite result since `(n+1/2)\pi` +cannot be represented exactly using floating-point arithmetic. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> sec(pi/3) + 2.0 + >>> sec(10000001) + -1.184723164360392819100265 + >>> sec(2+3j) + (-0.04167496441114427004834991 + 0.0906111371962375965296612j) + >>> sec(inf) + nan + >>> nprint(chop(taylor(sec, 0, 6))) + [1.0, 0.0, 0.5, 0.0, 0.208333, 0.0, 0.0847222] + +Intervals are supported via :func:`mpmath.iv.sec`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.sec([0,1]) + [1.0, 1.85081571768092561791175326276] + >>> iv.sec([0,2]) # Interval includes a singularity + [-inf, +inf] +""" + +csc = r""" +Computes the cosecant of `x`, `\mathrm{csc}(x) = \frac{1}{\sin(x)}`. +This cosecant function is singular at `x = n \pi`, but with the +exception of the point `x = 0`, ``csc(x)`` returns a finite result +since `n \pi` cannot be represented exactly using floating-point +arithmetic. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> csc(pi/3) + 1.154700538379251529018298 + >>> csc(10000001) + -1.864910497503629858938891 + >>> csc(2+3j) + (0.09047320975320743980579048 + 0.04120098628857412646300981j) + >>> csc(inf) + nan + +Intervals are supported via :func:`mpmath.iv.csc`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.csc([0,1]) # Interval includes a singularity + [1.18839510577812121626159943988, +inf] + >>> iv.csc([0,2]) + [1.0, +inf] +""" + +cot = r""" +Computes the cotangent of `x`, +`\mathrm{cot}(x) = \frac{1}{\tan(x)} = \frac{\cos(x)}{\sin(x)}`. +This cotangent function is singular at `x = n \pi`, but with the +exception of the point `x = 0`, ``cot(x)`` returns a finite result +since `n \pi` cannot be represented exactly using floating-point +arithmetic. + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> cot(pi/3) + 0.5773502691896257645091488 + >>> cot(10000001) + 1.574131876209625656003562 + >>> cot(2+3j) + (-0.003739710376336956660117409 - 0.9967577965693583104609688j) + >>> cot(inf) + nan + +Intervals are supported via :func:`mpmath.iv.cot`:: + + >>> iv.dps = 25; iv.pretty = True + >>> iv.cot([0,1]) # Interval includes a singularity + [0.642092615934330703006419974862, +inf] + >>> iv.cot([1,2]) + [-inf, +inf] +""" + +acos = r""" +Computes the inverse cosine or arccosine of `x`, `\cos^{-1}(x)`. +Since `-1 \le \cos(x) \le 1` for real `x`, the inverse +cosine is real-valued only for `-1 \le x \le 1`. On this interval, +:func:`~mpmath.acos` is defined to be a monotonically decreasing +function assuming values between `+\pi` and `0`. + +Basic values are:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> acos(-1) + 3.141592653589793238462643 + >>> acos(0) + 1.570796326794896619231322 + >>> acos(1) + 0.0 + >>> nprint(chop(taylor(acos, 0, 6))) + [1.5708, -1.0, 0.0, -0.166667, 0.0, -0.075, 0.0] + +:func:`~mpmath.acos` is defined so as to be a proper inverse function of +`\cos(\theta)` for `0 \le \theta < \pi`. +We have `\cos(\cos^{-1}(x)) = x` for all `x`, but +`\cos^{-1}(\cos(x)) = x` only for `0 \le \Re[x] < \pi`:: + + >>> for x in [1, 10, -1, 2+3j, 10+3j]: + ... print("%s %s" % (cos(acos(x)), acos(cos(x)))) + ... + 1.0 1.0 + (10.0 + 0.0j) 2.566370614359172953850574 + -1.0 1.0 + (2.0 + 3.0j) (2.0 + 3.0j) + (10.0 + 3.0j) (2.566370614359172953850574 - 3.0j) + +The inverse cosine has two branch points: `x = \pm 1`. :func:`~mpmath.acos` +places the branch cuts along the line segments `(-\infty, -1)` and +`(+1, +\infty)`. In general, + +.. math :: + + \cos^{-1}(x) = \frac{\pi}{2} + i \log\left(ix + \sqrt{1-x^2} \right) + +where the principal-branch log and square root are implied. +""" + +asin = r""" +Computes the inverse sine or arcsine of `x`, `\sin^{-1}(x)`. +Since `-1 \le \sin(x) \le 1` for real `x`, the inverse +sine is real-valued only for `-1 \le x \le 1`. +On this interval, it is defined to be a monotonically increasing +function assuming values between `-\pi/2` and `\pi/2`. + +Basic values are:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> asin(-1) + -1.570796326794896619231322 + >>> asin(0) + 0.0 + >>> asin(1) + 1.570796326794896619231322 + >>> nprint(chop(taylor(asin, 0, 6))) + [0.0, 1.0, 0.0, 0.166667, 0.0, 0.075, 0.0] + +:func:`~mpmath.asin` is defined so as to be a proper inverse function of +`\sin(\theta)` for `-\pi/2 < \theta < \pi/2`. +We have `\sin(\sin^{-1}(x)) = x` for all `x`, but +`\sin^{-1}(\sin(x)) = x` only for `-\pi/2 < \Re[x] < \pi/2`:: + + >>> for x in [1, 10, -1, 1+3j, -2+3j]: + ... print("%s %s" % (chop(sin(asin(x))), asin(sin(x)))) + ... + 1.0 1.0 + 10.0 -0.5752220392306202846120698 + -1.0 -1.0 + (1.0 + 3.0j) (1.0 + 3.0j) + (-2.0 + 3.0j) (-1.141592653589793238462643 - 3.0j) + +The inverse sine has two branch points: `x = \pm 1`. :func:`~mpmath.asin` +places the branch cuts along the line segments `(-\infty, -1)` and +`(+1, +\infty)`. In general, + +.. math :: + + \sin^{-1}(x) = -i \log\left(ix + \sqrt{1-x^2} \right) + +where the principal-branch log and square root are implied. +""" + +atan = r""" +Computes the inverse tangent or arctangent of `x`, `\tan^{-1}(x)`. +This is a real-valued function for all real `x`, with range +`(-\pi/2, \pi/2)`. + +Basic values are:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> atan(-inf) + -1.570796326794896619231322 + >>> atan(-1) + -0.7853981633974483096156609 + >>> atan(0) + 0.0 + >>> atan(1) + 0.7853981633974483096156609 + >>> atan(inf) + 1.570796326794896619231322 + >>> nprint(chop(taylor(atan, 0, 6))) + [0.0, 1.0, 0.0, -0.333333, 0.0, 0.2, 0.0] + +The inverse tangent is often used to compute angles. However, +the atan2 function is often better for this as it preserves sign +(see :func:`~mpmath.atan2`). + +:func:`~mpmath.atan` is defined so as to be a proper inverse function of +`\tan(\theta)` for `-\pi/2 < \theta < \pi/2`. +We have `\tan(\tan^{-1}(x)) = x` for all `x`, but +`\tan^{-1}(\tan(x)) = x` only for `-\pi/2 < \Re[x] < \pi/2`:: + + >>> mp.dps = 25 + >>> for x in [1, 10, -1, 1+3j, -2+3j]: + ... print("%s %s" % (tan(atan(x)), atan(tan(x)))) + ... + 1.0 1.0 + 10.0 0.5752220392306202846120698 + -1.0 -1.0 + (1.0 + 3.0j) (1.000000000000000000000001 + 3.0j) + (-2.0 + 3.0j) (1.141592653589793238462644 + 3.0j) + +The inverse tangent has two branch points: `x = \pm i`. :func:`~mpmath.atan` +places the branch cuts along the line segments `(-i \infty, -i)` and +`(+i, +i \infty)`. In general, + +.. math :: + + \tan^{-1}(x) = \frac{i}{2}\left(\log(1-ix)-\log(1+ix)\right) + +where the principal-branch log is implied. +""" + +acot = r"""Computes the inverse cotangent of `x`, +`\mathrm{cot}^{-1}(x) = \tan^{-1}(1/x)`.""" + +asec = r"""Computes the inverse secant of `x`, +`\mathrm{sec}^{-1}(x) = \cos^{-1}(1/x)`.""" + +acsc = r"""Computes the inverse cosecant of `x`, +`\mathrm{csc}^{-1}(x) = \sin^{-1}(1/x)`.""" + +coth = r"""Computes the hyperbolic cotangent of `x`, +`\mathrm{coth}(x) = \frac{\cosh(x)}{\sinh(x)}`. +""" + +sech = r"""Computes the hyperbolic secant of `x`, +`\mathrm{sech}(x) = \frac{1}{\cosh(x)}`. +""" + +csch = r"""Computes the hyperbolic cosecant of `x`, +`\mathrm{csch}(x) = \frac{1}{\sinh(x)}`. +""" + +acosh = r"""Computes the inverse hyperbolic cosine of `x`, +`\mathrm{cosh}^{-1}(x) = \log(x+\sqrt{x+1}\sqrt{x-1})`. +""" + +asinh = r"""Computes the inverse hyperbolic sine of `x`, +`\mathrm{sinh}^{-1}(x) = \log(x+\sqrt{1+x^2})`. +""" + +atanh = r"""Computes the inverse hyperbolic tangent of `x`, +`\mathrm{tanh}^{-1}(x) = \frac{1}{2}\left(\log(1+x)-\log(1-x)\right)`. +""" + +acoth = r"""Computes the inverse hyperbolic cotangent of `x`, +`\mathrm{coth}^{-1}(x) = \tanh^{-1}(1/x)`.""" + +asech = r"""Computes the inverse hyperbolic secant of `x`, +`\mathrm{sech}^{-1}(x) = \cosh^{-1}(1/x)`.""" + +acsch = r"""Computes the inverse hyperbolic cosecant of `x`, +`\mathrm{csch}^{-1}(x) = \sinh^{-1}(1/x)`.""" + + + +sinpi = r""" +Computes `\sin(\pi x)`, more accurately than the expression +``sin(pi*x)``:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> sinpi(10**10), sin(pi*(10**10)) + (0.0, -2.23936276195592e-6) + >>> sinpi(10**10+0.5), sin(pi*(10**10+0.5)) + (1.0, 0.999999999998721) +""" + +cospi = r""" +Computes `\cos(\pi x)`, more accurately than the expression +``cos(pi*x)``:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> cospi(10**10), cos(pi*(10**10)) + (1.0, 0.999999999997493) + >>> cospi(10**10+0.5), cos(pi*(10**10+0.5)) + (0.0, 1.59960492420134e-6) +""" + +sinc = r""" +``sinc(x)`` computes the unnormalized sinc function, defined as + +.. math :: + + \mathrm{sinc}(x) = \begin{cases} + \sin(x)/x, & \mbox{if } x \ne 0 \\ + 1, & \mbox{if } x = 0. + \end{cases} + +See :func:`~mpmath.sincpi` for the normalized sinc function. + +Simple values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> sinc(0) + 1.0 + >>> sinc(1) + 0.841470984807897 + >>> sinc(inf) + 0.0 + +The integral of the sinc function is the sine integral Si:: + + >>> quad(sinc, [0, 1]) + 0.946083070367183 + >>> si(1) + 0.946083070367183 +""" + +sincpi = r""" +``sincpi(x)`` computes the normalized sinc function, defined as + +.. math :: + + \mathrm{sinc}_{\pi}(x) = \begin{cases} + \sin(\pi x)/(\pi x), & \mbox{if } x \ne 0 \\ + 1, & \mbox{if } x = 0. + \end{cases} + +Equivalently, we have +`\mathrm{sinc}_{\pi}(x) = \mathrm{sinc}(\pi x)`. + +The normalization entails that the function integrates +to unity over the entire real line:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> quadosc(sincpi, [-inf, inf], period=2.0) + 1.0 + +Like, :func:`~mpmath.sinpi`, :func:`~mpmath.sincpi` is evaluated accurately +at its roots:: + + >>> sincpi(10) + 0.0 +""" + +expj = r""" +Convenience function for computing `e^{ix}`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> expj(0) + (1.0 + 0.0j) + >>> expj(-1) + (0.5403023058681397174009366 - 0.8414709848078965066525023j) + >>> expj(j) + (0.3678794411714423215955238 + 0.0j) + >>> expj(1+j) + (0.1987661103464129406288032 + 0.3095598756531121984439128j) +""" + +expjpi = r""" +Convenience function for computing `e^{i \pi x}`. +Evaluation is accurate near zeros (see also :func:`~mpmath.cospi`, +:func:`~mpmath.sinpi`):: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> expjpi(0) + (1.0 + 0.0j) + >>> expjpi(1) + (-1.0 + 0.0j) + >>> expjpi(0.5) + (0.0 + 1.0j) + >>> expjpi(-1) + (-1.0 + 0.0j) + >>> expjpi(j) + (0.04321391826377224977441774 + 0.0j) + >>> expjpi(1+j) + (-0.04321391826377224977441774 + 0.0j) +""" + +floor = r""" +Computes the floor of `x`, `\lfloor x \rfloor`, defined as +the largest integer less than or equal to `x`:: + + >>> from mpmath import * + >>> mp.pretty = False + >>> floor(3.5) + mpf('3.0') + +.. note :: + + :func:`~mpmath.floor`, :func:`~mpmath.ceil` and :func:`~mpmath.nint` return a + floating-point number, not a Python ``int``. If `\lfloor x \rfloor` is + too large to be represented exactly at the present working precision, + the result will be rounded, not necessarily in the direction + implied by the mathematical definition of the function. + +To avoid rounding, use *prec=0*:: + + >>> mp.dps = 15 + >>> print(int(floor(10**30+1))) + 1000000000000000019884624838656 + >>> print(int(floor(10**30+1, prec=0))) + 1000000000000000000000000000001 + +The floor function is defined for complex numbers and +acts on the real and imaginary parts separately:: + + >>> floor(3.25+4.75j) + mpc(real='3.0', imag='4.0') +""" + +ceil = r""" +Computes the ceiling of `x`, `\lceil x \rceil`, defined as +the smallest integer greater than or equal to `x`:: + + >>> from mpmath import * + >>> mp.pretty = False + >>> ceil(3.5) + mpf('4.0') + +The ceiling function is defined for complex numbers and +acts on the real and imaginary parts separately:: + + >>> ceil(3.25+4.75j) + mpc(real='4.0', imag='5.0') + +See notes about rounding for :func:`~mpmath.floor`. +""" + +nint = r""" +Evaluates the nearest integer function, `\mathrm{nint}(x)`. +This gives the nearest integer to `x`; on a tie, it +gives the nearest even integer:: + + >>> from mpmath import * + >>> mp.pretty = False + >>> nint(3.2) + mpf('3.0') + >>> nint(3.8) + mpf('4.0') + >>> nint(3.5) + mpf('4.0') + >>> nint(4.5) + mpf('4.0') + +The nearest integer function is defined for complex numbers and +acts on the real and imaginary parts separately:: + + >>> nint(3.25+4.75j) + mpc(real='3.0', imag='5.0') + +See notes about rounding for :func:`~mpmath.floor`. +""" + +frac = r""" +Gives the fractional part of `x`, defined as +`\mathrm{frac}(x) = x - \lfloor x \rfloor` (see :func:`~mpmath.floor`). +In effect, this computes `x` modulo 1, or `x+n` where +`n \in \mathbb{Z}` is such that `x+n \in [0,1)`:: + + >>> from mpmath import * + >>> mp.pretty = False + >>> frac(1.25) + mpf('0.25') + >>> frac(3) + mpf('0.0') + >>> frac(-1.25) + mpf('0.75') + +For a complex number, the fractional part function applies to +the real and imaginary parts separately:: + + >>> frac(2.25+3.75j) + mpc(real='0.25', imag='0.75') + +Plotted, the fractional part function gives a sawtooth +wave. The Fourier series coefficients have a simple +form:: + + >>> mp.dps = 15 + >>> nprint(fourier(lambda x: frac(x)-0.5, [0,1], 4)) + ([0.0, 0.0, 0.0, 0.0, 0.0], [0.0, -0.31831, -0.159155, -0.106103, -0.0795775]) + >>> nprint([-1/(pi*k) for k in range(1,5)]) + [-0.31831, -0.159155, -0.106103, -0.0795775] + +.. note:: + + The fractional part is sometimes defined as a symmetric + function, i.e. returning `-\mathrm{frac}(-x)` if `x < 0`. + This convention is used, for instance, by Mathematica's + ``FractionalPart``. + +""" + +sign = r""" +Returns the sign of `x`, defined as `\mathrm{sign}(x) = x / |x|` +(with the special case `\mathrm{sign}(0) = 0`):: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> sign(10) + mpf('1.0') + >>> sign(-10) + mpf('-1.0') + >>> sign(0) + mpf('0.0') + +Note that the sign function is also defined for complex numbers, +for which it gives the projection onto the unit circle:: + + >>> mp.dps = 15; mp.pretty = True + >>> sign(1+j) + (0.707106781186547 + 0.707106781186547j) + +""" + +arg = r""" +Computes the complex argument (phase) of `x`, defined as the +signed angle between the positive real axis and `x` in the +complex plane:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> arg(3) + 0.0 + >>> arg(3+3j) + 0.785398163397448 + >>> arg(3j) + 1.5707963267949 + >>> arg(-3) + 3.14159265358979 + >>> arg(-3j) + -1.5707963267949 + +The angle is defined to satisfy `-\pi < \arg(x) \le \pi` and +with the sign convention that a nonnegative imaginary part +results in a nonnegative argument. + +The value returned by :func:`~mpmath.arg` is an ``mpf`` instance. +""" + +fabs = r""" +Returns the absolute value of `x`, `|x|`. Unlike :func:`abs`, +:func:`~mpmath.fabs` converts non-mpmath numbers (such as ``int``) +into mpmath numbers:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> fabs(3) + mpf('3.0') + >>> fabs(-3) + mpf('3.0') + >>> fabs(3+4j) + mpf('5.0') +""" + +re = r""" +Returns the real part of `x`, `\Re(x)`. :func:`~mpmath.re` +converts a non-mpmath number to an mpmath number:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> re(3) + mpf('3.0') + >>> re(-1+4j) + mpf('-1.0') +""" + +im = r""" +Returns the imaginary part of `x`, `\Im(x)`. :func:`~mpmath.im` +converts a non-mpmath number to an mpmath number:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> im(3) + mpf('0.0') + >>> im(-1+4j) + mpf('4.0') +""" + +conj = r""" +Returns the complex conjugate of `x`, `\overline{x}`. Unlike +``x.conjugate()``, :func:`~mpmath.im` converts `x` to a mpmath number:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> conj(3) + mpf('3.0') + >>> conj(-1+4j) + mpc(real='-1.0', imag='-4.0') +""" + +polar = r""" +Returns the polar representation of the complex number `z` +as a pair `(r, \phi)` such that `z = r e^{i \phi}`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> polar(-2) + (2.0, 3.14159265358979) + >>> polar(3-4j) + (5.0, -0.927295218001612) +""" + +rect = r""" +Returns the complex number represented by polar +coordinates `(r, \phi)`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> chop(rect(2, pi)) + -2.0 + >>> rect(sqrt(2), -pi/4) + (1.0 - 1.0j) +""" + +expm1 = r""" +Computes `e^x - 1`, accurately for small `x`. + +Unlike the expression ``exp(x) - 1``, ``expm1(x)`` does not suffer from +potentially catastrophic cancellation:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> exp(1e-10)-1; print(expm1(1e-10)) + 1.00000008274037e-10 + 1.00000000005e-10 + >>> exp(1e-20)-1; print(expm1(1e-20)) + 0.0 + 1.0e-20 + >>> 1/(exp(1e-20)-1) + Traceback (most recent call last): + ... + ZeroDivisionError + >>> 1/expm1(1e-20) + 1.0e+20 + +Evaluation works for extremely tiny values:: + + >>> expm1(0) + 0.0 + >>> expm1('1e-10000000') + 1.0e-10000000 + +""" + +log1p = r""" +Computes `\log(1+x)`, accurately for small `x`. + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> log(1+1e-10); print(mp.log1p(1e-10)) + 1.00000008269037e-10 + 9.9999999995e-11 + >>> mp.log1p(1e-100j) + (5.0e-201 + 1.0e-100j) + >>> mp.log1p(0) + 0.0 + +""" + + +powm1 = r""" +Computes `x^y - 1`, accurately when `x^y` is very close to 1. + +This avoids potentially catastrophic cancellation:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> power(0.99999995, 1e-10) - 1 + 0.0 + >>> powm1(0.99999995, 1e-10) + -5.00000012791934e-18 + +Powers exactly equal to 1, and only those powers, yield 0 exactly:: + + >>> powm1(-j, 4) + (0.0 + 0.0j) + >>> powm1(3, 0) + 0.0 + >>> powm1(fadd(-1, 1e-100, exact=True), 4) + -4.0e-100 + +Evaluation works for extremely tiny `y`:: + + >>> powm1(2, '1e-100000') + 6.93147180559945e-100001 + >>> powm1(j, '1e-1000') + (-1.23370055013617e-2000 + 1.5707963267949e-1000j) + +""" + +root = r""" +``root(z, n, k=0)`` computes an `n`-th root of `z`, i.e. returns a number +`r` that (up to possible approximation error) satisfies `r^n = z`. +(``nthroot`` is available as an alias for ``root``.) + +Every complex number `z \ne 0` has `n` distinct `n`-th roots, which are +equidistant points on a circle with radius `|z|^{1/n}`, centered around the +origin. A specific root may be selected using the optional index +`k`. The roots are indexed counterclockwise, starting with `k = 0` for the root +closest to the positive real half-axis. + +The `k = 0` root is the so-called principal `n`-th root, often denoted by +`\sqrt[n]{z}` or `z^{1/n}`, and also given by `\exp(\log(z) / n)`. If `z` is +a positive real number, the principal root is just the unique positive +`n`-th root of `z`. Under some circumstances, non-principal real roots exist: +for positive real `z`, `n` even, there is a negative root given by `k = n/2`; +for negative real `z`, `n` odd, there is a negative root given by `k = (n-1)/2`. + +To obtain all roots with a simple expression, use +``[root(z,n,k) for k in range(n)]``. + +An important special case, ``root(1, n, k)`` returns the `k`-th `n`-th root of +unity, `\zeta_k = e^{2 \pi i k / n}`. Alternatively, :func:`~mpmath.unitroots` +provides a slightly more convenient way to obtain the roots of unity, +including the option to compute only the primitive roots of unity. + +Both `k` and `n` should be integers; `k` outside of ``range(n)`` will be +reduced modulo `n`. If `n` is negative, `x^{-1/n} = 1/x^{1/n}` (or +the equivalent reciprocal for a non-principal root with `k \ne 0`) is computed. + +:func:`~mpmath.root` is implemented to use Newton's method for small +`n`. At high precision, this makes `x^{1/n}` not much more +expensive than the regular exponentiation, `x^n`. For very large +`n`, :func:`~mpmath.nthroot` falls back to use the exponential function. + +**Examples** + +:func:`~mpmath.nthroot`/:func:`~mpmath.root` is faster and more accurate than raising to a +floating-point fraction:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = False + >>> 16807 ** (mpf(1)/5) + mpf('7.0000000000000009') + >>> root(16807, 5) + mpf('7.0') + >>> nthroot(16807, 5) # Alias + mpf('7.0') + +A high-precision root:: + + >>> mp.dps = 50; mp.pretty = True + >>> nthroot(10, 5) + 1.584893192461113485202101373391507013269442133825 + >>> nthroot(10, 5) ** 5 + 10.0 + +Computing principal and non-principal square and cube roots:: + + >>> mp.dps = 15 + >>> root(10, 2) + 3.16227766016838 + >>> root(10, 2, 1) + -3.16227766016838 + >>> root(-10, 3) + (1.07721734501594 + 1.86579517236206j) + >>> root(-10, 3, 1) + -2.15443469003188 + >>> root(-10, 3, 2) + (1.07721734501594 - 1.86579517236206j) + +All the 7th roots of a complex number:: + + >>> for r in [root(3+4j, 7, k) for k in range(7)]: + ... print("%s %s" % (r, r**7)) + ... + (1.24747270589553 + 0.166227124177353j) (3.0 + 4.0j) + (0.647824911301003 + 1.07895435170559j) (3.0 + 4.0j) + (-0.439648254723098 + 1.17920694574172j) (3.0 + 4.0j) + (-1.19605731775069 + 0.391492658196305j) (3.0 + 4.0j) + (-1.05181082538903 - 0.691023585965793j) (3.0 + 4.0j) + (-0.115529328478668 - 1.25318497558335j) (3.0 + 4.0j) + (0.907748109144957 - 0.871672518271819j) (3.0 + 4.0j) + +Cube roots of unity:: + + >>> for k in range(3): print(root(1, 3, k)) + ... + 1.0 + (-0.5 + 0.866025403784439j) + (-0.5 - 0.866025403784439j) + +Some exact high order roots:: + + >>> root(75**210, 105) + 5625.0 + >>> root(1, 128, 96) + (0.0 - 1.0j) + >>> root(4**128, 128, 96) + (0.0 - 4.0j) + +""" + +unitroots = r""" +``unitroots(n)`` returns `\zeta_0, \zeta_1, \ldots, \zeta_{n-1}`, +all the distinct `n`-th roots of unity, as a list. If the option +*primitive=True* is passed, only the primitive roots are returned. + +Every `n`-th root of unity satisfies `(\zeta_k)^n = 1`. There are `n` distinct +roots for each `n` (`\zeta_k` and `\zeta_j` are the same when +`k = j \pmod n`), which form a regular polygon with vertices on the unit +circle. They are ordered counterclockwise with increasing `k`, starting +with `\zeta_0 = 1`. + +**Examples** + +The roots of unity up to `n = 4`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> nprint(unitroots(1)) + [1.0] + >>> nprint(unitroots(2)) + [1.0, -1.0] + >>> nprint(unitroots(3)) + [1.0, (-0.5 + 0.866025j), (-0.5 - 0.866025j)] + >>> nprint(unitroots(4)) + [1.0, (0.0 + 1.0j), -1.0, (0.0 - 1.0j)] + +Roots of unity form a geometric series that sums to 0:: + + >>> mp.dps = 50 + >>> chop(fsum(unitroots(25))) + 0.0 + +Primitive roots up to `n = 4`:: + + >>> mp.dps = 15 + >>> nprint(unitroots(1, primitive=True)) + [1.0] + >>> nprint(unitroots(2, primitive=True)) + [-1.0] + >>> nprint(unitroots(3, primitive=True)) + [(-0.5 + 0.866025j), (-0.5 - 0.866025j)] + >>> nprint(unitroots(4, primitive=True)) + [(0.0 + 1.0j), (0.0 - 1.0j)] + +There are only four primitive 12th roots:: + + >>> nprint(unitroots(12, primitive=True)) + [(0.866025 + 0.5j), (-0.866025 + 0.5j), (-0.866025 - 0.5j), (0.866025 - 0.5j)] + +The `n`-th roots of unity form a group, the cyclic group of order `n`. +Any primitive root `r` is a generator for this group, meaning that +`r^0, r^1, \ldots, r^{n-1}` gives the whole set of unit roots (in +some permuted order):: + + >>> for r in unitroots(6): print(r) + ... + 1.0 + (0.5 + 0.866025403784439j) + (-0.5 + 0.866025403784439j) + -1.0 + (-0.5 - 0.866025403784439j) + (0.5 - 0.866025403784439j) + >>> r = unitroots(6, primitive=True)[1] + >>> for k in range(6): print(chop(r**k)) + ... + 1.0 + (0.5 - 0.866025403784439j) + (-0.5 - 0.866025403784439j) + -1.0 + (-0.5 + 0.866025403784438j) + (0.5 + 0.866025403784438j) + +The number of primitive roots equals the Euler totient function `\phi(n)`:: + + >>> [len(unitroots(n, primitive=True)) for n in range(1,20)] + [1, 1, 2, 2, 4, 2, 6, 4, 6, 4, 10, 4, 12, 6, 8, 8, 16, 6, 18] + +""" + + +log = r""" +Computes the base-`b` logarithm of `x`, `\log_b(x)`. If `b` is +unspecified, :func:`~mpmath.log` computes the natural (base `e`) logarithm +and is equivalent to :func:`~mpmath.ln`. In general, the base `b` logarithm +is defined in terms of the natural logarithm as +`\log_b(x) = \ln(x)/\ln(b)`. + +By convention, we take `\log(0) = -\infty`. + +The natural logarithm is real if `x > 0` and complex if `x < 0` or if +`x` is complex. The principal branch of the complex logarithm is +used, meaning that `\Im(\ln(x)) = -\pi < \arg(x) \le \pi`. + +**Examples** + +Some basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> log(1) + 0.0 + >>> log(2) + 0.693147180559945 + >>> log(1000,10) + 3.0 + >>> log(4, 16) + 0.5 + >>> log(j) + (0.0 + 1.5707963267949j) + >>> log(-1) + (0.0 + 3.14159265358979j) + >>> log(0) + -inf + >>> log(inf) + +inf + +The natural logarithm is the antiderivative of `1/x`:: + + >>> quad(lambda x: 1/x, [1, 5]) + 1.6094379124341 + >>> log(5) + 1.6094379124341 + >>> diff(log, 10) + 0.1 + +The Taylor series expansion of the natural logarithm around +`x = 1` has coefficients `(-1)^{n+1}/n`:: + + >>> nprint(taylor(log, 1, 7)) + [0.0, 1.0, -0.5, 0.333333, -0.25, 0.2, -0.166667, 0.142857] + +:func:`~mpmath.log` supports arbitrary precision evaluation:: + + >>> mp.dps = 50 + >>> log(pi) + 1.1447298858494001741434273513530587116472948129153 + >>> log(pi, pi**3) + 0.33333333333333333333333333333333333333333333333333 + >>> mp.dps = 25 + >>> log(3+4j) + (1.609437912434100374600759 + 0.9272952180016122324285125j) +""" + +log10 = r""" +Computes the base-10 logarithm of `x`, `\log_{10}(x)`. ``log10(x)`` +is equivalent to ``log(x, 10)``. +""" + +fmod = r""" +Converts `x` and `y` to mpmath numbers and returns `x \mod y`. +For mpmath numbers, this is equivalent to ``x % y``. + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> fmod(100, pi) + 2.61062773871641 + +You can use :func:`~mpmath.fmod` to compute fractional parts of numbers:: + + >>> fmod(10.25, 1) + 0.25 + +""" + +radians = r""" +Converts the degree angle `x` to radians:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> radians(60) + 1.0471975511966 +""" + +degrees = r""" +Converts the radian angle `x` to a degree angle:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> degrees(pi/3) + 60.0 +""" + +atan2 = r""" +Computes the two-argument arctangent, `\mathrm{atan2}(y, x)`, +giving the signed angle between the positive `x`-axis and the +point `(x, y)` in the 2D plane. This function is defined for +real `x` and `y` only. + +The two-argument arctangent essentially computes +`\mathrm{atan}(y/x)`, but accounts for the signs of both +`x` and `y` to give the angle for the correct quadrant. The +following examples illustrate the difference:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> atan2(1,1), atan(1/1.) + (0.785398163397448, 0.785398163397448) + >>> atan2(1,-1), atan(1/-1.) + (2.35619449019234, -0.785398163397448) + >>> atan2(-1,1), atan(-1/1.) + (-0.785398163397448, -0.785398163397448) + >>> atan2(-1,-1), atan(-1/-1.) + (-2.35619449019234, 0.785398163397448) + +The angle convention is the same as that used for the complex +argument; see :func:`~mpmath.arg`. +""" + +fibonacci = r""" +``fibonacci(n)`` computes the `n`-th Fibonacci number, `F(n)`. The +Fibonacci numbers are defined by the recurrence `F(n) = F(n-1) + F(n-2)` +with the initial values `F(0) = 0`, `F(1) = 1`. :func:`~mpmath.fibonacci` +extends this definition to arbitrary real and complex arguments +using the formula + +.. math :: + + F(z) = \frac{\phi^z - \cos(\pi z) \phi^{-z}}{\sqrt 5} + +where `\phi` is the golden ratio. :func:`~mpmath.fibonacci` also uses this +continuous formula to compute `F(n)` for extremely large `n`, where +calculating the exact integer would be wasteful. + +For convenience, :func:`~mpmath.fib` is available as an alias for +:func:`~mpmath.fibonacci`. + +**Basic examples** + +Some small Fibonacci numbers are:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for i in range(10): + ... print(fibonacci(i)) + ... + 0.0 + 1.0 + 1.0 + 2.0 + 3.0 + 5.0 + 8.0 + 13.0 + 21.0 + 34.0 + >>> fibonacci(50) + 12586269025.0 + +The recurrence for `F(n)` extends backwards to negative `n`:: + + >>> for i in range(10): + ... print(fibonacci(-i)) + ... + 0.0 + 1.0 + -1.0 + 2.0 + -3.0 + 5.0 + -8.0 + 13.0 + -21.0 + 34.0 + +Large Fibonacci numbers will be computed approximately unless +the precision is set high enough:: + + >>> fib(200) + 2.8057117299251e+41 + >>> mp.dps = 45 + >>> fib(200) + 280571172992510140037611932413038677189525.0 + +:func:`~mpmath.fibonacci` can compute approximate Fibonacci numbers +of stupendous size:: + + >>> mp.dps = 15 + >>> fibonacci(10**25) + 3.49052338550226e+2089876402499787337692720 + +**Real and complex arguments** + +The extended Fibonacci function is an analytic function. The +property `F(z) = F(z-1) + F(z-2)` holds for arbitrary `z`:: + + >>> mp.dps = 15 + >>> fib(pi) + 2.1170270579161 + >>> fib(pi-1) + fib(pi-2) + 2.1170270579161 + >>> fib(3+4j) + (-5248.51130728372 - 14195.962288353j) + >>> fib(2+4j) + fib(1+4j) + (-5248.51130728372 - 14195.962288353j) + +The Fibonacci function has infinitely many roots on the +negative half-real axis. The first root is at 0, the second is +close to -0.18, and then there are infinitely many roots that +asymptotically approach `-n+1/2`:: + + >>> findroot(fib, -0.2) + -0.183802359692956 + >>> findroot(fib, -2) + -1.57077646820395 + >>> findroot(fib, -17) + -16.4999999596115 + >>> findroot(fib, -24) + -23.5000000000479 + +**Mathematical relationships** + +For large `n`, `F(n+1)/F(n)` approaches the golden ratio:: + + >>> mp.dps = 50 + >>> fibonacci(101)/fibonacci(100) + 1.6180339887498948482045868343656381177203127439638 + >>> +phi + 1.6180339887498948482045868343656381177203091798058 + +The sum of reciprocal Fibonacci numbers converges to an irrational +number for which no closed form expression is known:: + + >>> mp.dps = 15 + >>> nsum(lambda n: 1/fib(n), [1, inf]) + 3.35988566624318 + +Amazingly, however, the sum of odd-index reciprocal Fibonacci +numbers can be expressed in terms of a Jacobi theta function:: + + >>> nsum(lambda n: 1/fib(2*n+1), [0, inf]) + 1.82451515740692 + >>> sqrt(5)*jtheta(2,0,(3-sqrt(5))/2)**2/4 + 1.82451515740692 + +Some related sums can be done in closed form:: + + >>> nsum(lambda k: 1/(1+fib(2*k+1)), [0, inf]) + 1.11803398874989 + >>> phi - 0.5 + 1.11803398874989 + >>> f = lambda k:(-1)**(k+1) / sum(fib(n)**2 for n in range(1,int(k+1))) + >>> nsum(f, [1, inf]) + 0.618033988749895 + >>> phi-1 + 0.618033988749895 + +**References** + +1. http://mathworld.wolfram.com/FibonacciNumber.html +""" + +altzeta = r""" +Gives the Dirichlet eta function, `\eta(s)`, also known as the +alternating zeta function. This function is defined in analogy +with the Riemann zeta function as providing the sum of the +alternating series + +.. math :: + + \eta(s) = \sum_{k=0}^{\infty} \frac{(-1)^k}{k^s} + = 1-\frac{1}{2^s}+\frac{1}{3^s}-\frac{1}{4^s}+\ldots + +The eta function, unlike the Riemann zeta function, is an entire +function, having a finite value for all complex `s`. The special case +`\eta(1) = \log(2)` gives the value of the alternating harmonic series. + +The alternating zeta function may expressed using the Riemann zeta function +as `\eta(s) = (1 - 2^{1-s}) \zeta(s)`. It can also be expressed +in terms of the Hurwitz zeta function, for example using +:func:`~mpmath.dirichlet` (see documentation for that function). + +**Examples** + +Some special values are:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> altzeta(1) + 0.693147180559945 + >>> altzeta(0) + 0.5 + >>> altzeta(-1) + 0.25 + >>> altzeta(-2) + 0.0 + +An example of a sum that can be computed more accurately and +efficiently via :func:`~mpmath.altzeta` than via numerical summation:: + + >>> sum(-(-1)**n / mpf(n)**2.5 for n in range(1, 100)) + 0.867204951503984 + >>> altzeta(2.5) + 0.867199889012184 + +At positive even integers, the Dirichlet eta function +evaluates to a rational multiple of a power of `\pi`:: + + >>> altzeta(2) + 0.822467033424113 + >>> pi**2/12 + 0.822467033424113 + +Like the Riemann zeta function, `\eta(s)`, approaches 1 +as `s` approaches positive infinity, although it does +so from below rather than from above:: + + >>> altzeta(30) + 0.999999999068682 + >>> altzeta(inf) + 1.0 + >>> mp.pretty = False + >>> altzeta(1000, rounding='d') + mpf('0.99999999999999989') + >>> altzeta(1000, rounding='u') + mpf('1.0') + +**References** + +1. http://mathworld.wolfram.com/DirichletEtaFunction.html + +2. http://en.wikipedia.org/wiki/Dirichlet_eta_function +""" + +factorial = r""" +Computes the factorial, `x!`. For integers `n \ge 0`, we have +`n! = 1 \cdot 2 \cdots (n-1) \cdot n` and more generally the factorial +is defined for real or complex `x` by `x! = \Gamma(x+1)`. + +**Examples** + +Basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for k in range(6): + ... print("%s %s" % (k, fac(k))) + ... + 0 1.0 + 1 1.0 + 2 2.0 + 3 6.0 + 4 24.0 + 5 120.0 + >>> fac(inf) + +inf + >>> fac(0.5), sqrt(pi)/2 + (0.886226925452758, 0.886226925452758) + +For large positive `x`, `x!` can be approximated by +Stirling's formula:: + + >>> x = 10**10 + >>> fac(x) + 2.32579620567308e+95657055186 + >>> sqrt(2*pi*x)*(x/e)**x + 2.32579597597705e+95657055186 + +:func:`~mpmath.fac` supports evaluation for astronomically large values:: + + >>> fac(10**30) + 6.22311232304258e+29565705518096748172348871081098 + +Reciprocal factorials appear in the Taylor series of the +exponential function (among many other contexts):: + + >>> nsum(lambda k: 1/fac(k), [0, inf]), exp(1) + (2.71828182845905, 2.71828182845905) + >>> nsum(lambda k: pi**k/fac(k), [0, inf]), exp(pi) + (23.1406926327793, 23.1406926327793) + +""" + +gamma = r""" +Computes the gamma function, `\Gamma(x)`. The gamma function is a +shifted version of the ordinary factorial, satisfying +`\Gamma(n) = (n-1)!` for integers `n > 0`. More generally, it +is defined by + +.. math :: + + \Gamma(x) = \int_0^{\infty} t^{x-1} e^{-t}\, dt + +for any real or complex `x` with `\Re(x) > 0` and for `\Re(x) < 0` +by analytic continuation. + +**Examples** + +Basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for k in range(1, 6): + ... print("%s %s" % (k, gamma(k))) + ... + 1 1.0 + 2 1.0 + 3 2.0 + 4 6.0 + 5 24.0 + >>> gamma(inf) + +inf + >>> gamma(0) + Traceback (most recent call last): + ... + ValueError: gamma function pole + +The gamma function of a half-integer is a rational multiple of +`\sqrt{\pi}`:: + + >>> gamma(0.5), sqrt(pi) + (1.77245385090552, 1.77245385090552) + >>> gamma(1.5), sqrt(pi)/2 + (0.886226925452758, 0.886226925452758) + +We can check the integral definition:: + + >>> gamma(3.5) + 3.32335097044784 + >>> quad(lambda t: t**2.5*exp(-t), [0,inf]) + 3.32335097044784 + +:func:`~mpmath.gamma` supports arbitrary-precision evaluation and +complex arguments:: + + >>> mp.dps = 50 + >>> gamma(sqrt(3)) + 0.91510229697308632046045539308226554038315280564184 + >>> mp.dps = 25 + >>> gamma(2j) + (0.009902440080927490985955066 - 0.07595200133501806872408048j) + +Arguments can also be large. Note that the gamma function grows +very quickly:: + + >>> mp.dps = 15 + >>> gamma(10**20) + 1.9328495143101e+1956570551809674817225 + +**References** + +* [Spouge]_ + +""" + +psi = r""" +Gives the polygamma function of order `m` of `z`, `\psi^{(m)}(z)`. +Special cases are known as the *digamma function* (`\psi^{(0)}(z)`), +the *trigamma function* (`\psi^{(1)}(z)`), etc. The polygamma +functions are defined as the logarithmic derivatives of the gamma +function: + +.. math :: + + \psi^{(m)}(z) = \left(\frac{d}{dz}\right)^{m+1} \log \Gamma(z) + +In particular, `\psi^{(0)}(z) = \Gamma'(z)/\Gamma(z)`. In the +present implementation of :func:`~mpmath.psi`, the order `m` must be a +nonnegative integer, while the argument `z` may be an arbitrary +complex number (with exception for the polygamma function's poles +at `z = 0, -1, -2, \ldots`). + +**Examples** + +For various rational arguments, the polygamma function reduces to +a combination of standard mathematical constants:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> psi(0, 1), -euler + (-0.5772156649015328606065121, -0.5772156649015328606065121) + >>> psi(1, '1/4'), pi**2+8*catalan + (17.19732915450711073927132, 17.19732915450711073927132) + >>> psi(2, '1/2'), -14*apery + (-16.82879664423431999559633, -16.82879664423431999559633) + +The polygamma functions are derivatives of each other:: + + >>> diff(lambda x: psi(3, x), pi), psi(4, pi) + (-0.1105749312578862734526952, -0.1105749312578862734526952) + >>> quad(lambda x: psi(4, x), [2, 3]), psi(3,3)-psi(3,2) + (-0.375, -0.375) + +The digamma function diverges logarithmically as `z \to \infty`, +while higher orders tend to zero:: + + >>> psi(0,inf), psi(1,inf), psi(2,inf) + (+inf, 0.0, 0.0) + +Evaluation for a complex argument:: + + >>> psi(2, -1-2j) + (0.03902435405364952654838445 + 0.1574325240413029954685366j) + +Evaluation is supported for large orders `m` and/or large +arguments `z`:: + + >>> psi(3, 10**100) + 2.0e-300 + >>> psi(250, 10**30+10**20*j) + (-1.293142504363642687204865e-7010 + 3.232856260909107391513108e-7018j) + +**Application to infinite series** + +Any infinite series where the summand is a rational function of +the index `k` can be evaluated in closed form in terms of polygamma +functions of the roots and poles of the summand:: + + >>> a = sqrt(2) + >>> b = sqrt(3) + >>> nsum(lambda k: 1/((k+a)**2*(k+b)), [0, inf]) + 0.4049668927517857061917531 + >>> (psi(0,a)-psi(0,b)-a*psi(1,a)+b*psi(1,a))/(a-b)**2 + 0.4049668927517857061917531 + +This follows from the series representation (`m > 0`) + +.. math :: + + \psi^{(m)}(z) = (-1)^{m+1} m! \sum_{k=0}^{\infty} + \frac{1}{(z+k)^{m+1}}. + +Since the roots of a polynomial may be complex, it is sometimes +necessary to use the complex polygamma function to evaluate +an entirely real-valued sum:: + + >>> nsum(lambda k: 1/(k**2-2*k+3), [0, inf]) + 1.694361433907061256154665 + >>> nprint(polyroots([1,-2,3])) + [(1.0 - 1.41421j), (1.0 + 1.41421j)] + >>> r1 = 1-sqrt(2)*j + >>> r2 = r1.conjugate() + >>> (psi(0,-r2)-psi(0,-r1))/(r1-r2) + (1.694361433907061256154665 + 0.0j) + +""" + +digamma = r""" +Shortcut for ``psi(0,z)``. +""" + +harmonic = r""" +If `n` is an integer, ``harmonic(n)`` gives a floating-point +approximation of the `n`-th harmonic number `H(n)`, defined as + +.. math :: + + H(n) = 1 + \frac{1}{2} + \frac{1}{3} + \ldots + \frac{1}{n} + +The first few harmonic numbers are:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(8): + ... print("%s %s" % (n, harmonic(n))) + ... + 0 0.0 + 1 1.0 + 2 1.5 + 3 1.83333333333333 + 4 2.08333333333333 + 5 2.28333333333333 + 6 2.45 + 7 2.59285714285714 + +The infinite harmonic series `1 + 1/2 + 1/3 + \ldots` diverges:: + + >>> harmonic(inf) + +inf + +:func:`~mpmath.harmonic` is evaluated using the digamma function rather +than by summing the harmonic series term by term. It can therefore +be computed quickly for arbitrarily large `n`, and even for +nonintegral arguments:: + + >>> harmonic(10**100) + 230.835724964306 + >>> harmonic(0.5) + 0.613705638880109 + >>> harmonic(3+4j) + (2.24757548223494 + 0.850502209186044j) + +:func:`~mpmath.harmonic` supports arbitrary precision evaluation:: + + >>> mp.dps = 50 + >>> harmonic(11) + 3.0198773448773448773448773448773448773448773448773 + >>> harmonic(pi) + 1.8727388590273302654363491032336134987519132374152 + +The harmonic series diverges, but at a glacial pace. It is possible +to calculate the exact number of terms required before the sum +exceeds a given amount, say 100:: + + >>> mp.dps = 50 + >>> v = 10**findroot(lambda x: harmonic(10**x) - 100, 10) + >>> v + 15092688622113788323693563264538101449859496.864101 + >>> v = int(ceil(v)) + >>> print(v) + 15092688622113788323693563264538101449859497 + >>> harmonic(v-1) + 99.999999999999999999999999999999999999999999942747 + >>> harmonic(v) + 100.000000000000000000000000000000000000000000009 + +""" + +bernoulli = r""" +Computes the nth Bernoulli number, `B_n`, for any integer `n \ge 0`. + +The Bernoulli numbers are rational numbers, but this function +returns a floating-point approximation. To obtain an exact +fraction, use :func:`~mpmath.bernfrac` instead. + +**Examples** + +Numerical values of the first few Bernoulli numbers:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(15): + ... print("%s %s" % (n, bernoulli(n))) + ... + 0 1.0 + 1 -0.5 + 2 0.166666666666667 + 3 0.0 + 4 -0.0333333333333333 + 5 0.0 + 6 0.0238095238095238 + 7 0.0 + 8 -0.0333333333333333 + 9 0.0 + 10 0.0757575757575758 + 11 0.0 + 12 -0.253113553113553 + 13 0.0 + 14 1.16666666666667 + +Bernoulli numbers can be approximated with arbitrary precision:: + + >>> mp.dps = 50 + >>> bernoulli(100) + -2.8382249570693706959264156336481764738284680928013e+78 + +Arbitrarily large `n` are supported:: + + >>> mp.dps = 15 + >>> bernoulli(10**20 + 2) + 3.09136296657021e+1876752564973863312327 + +The Bernoulli numbers are related to the Riemann zeta function +at integer arguments:: + + >>> -bernoulli(8) * (2*pi)**8 / (2*fac(8)) + 1.00407735619794 + >>> zeta(8) + 1.00407735619794 + +**Algorithm** + +For small `n` (`n < 3000`) :func:`~mpmath.bernoulli` uses a recurrence +formula due to Ramanujan. All results in this range are cached, +so sequential computation of small Bernoulli numbers is +guaranteed to be fast. + +For larger `n`, `B_n` is evaluated in terms of the Riemann zeta +function. +""" + +stieltjes = r""" +For a nonnegative integer `n`, ``stieltjes(n)`` computes the +`n`-th Stieltjes constant `\gamma_n`, defined as the +`n`-th coefficient in the Laurent series expansion of the +Riemann zeta function around the pole at `s = 1`. That is, +we have: + +.. math :: + + \zeta(s) = \frac{1}{s-1} \sum_{n=0}^{\infty} + \frac{(-1)^n}{n!} \gamma_n (s-1)^n + +More generally, ``stieltjes(n, a)`` gives the corresponding +coefficient `\gamma_n(a)` for the Hurwitz zeta function +`\zeta(s,a)` (with `\gamma_n = \gamma_n(1)`). + +**Examples** + +The zeroth Stieltjes constant is just Euler's constant `\gamma`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> stieltjes(0) + 0.577215664901533 + +Some more values are:: + + >>> stieltjes(1) + -0.0728158454836767 + >>> stieltjes(10) + 0.000205332814909065 + >>> stieltjes(30) + 0.00355772885557316 + >>> stieltjes(1000) + -1.57095384420474e+486 + >>> stieltjes(2000) + 2.680424678918e+1109 + >>> stieltjes(1, 2.5) + -0.23747539175716 + +An alternative way to compute `\gamma_1`:: + + >>> diff(extradps(15)(lambda x: 1/(x-1) - zeta(x)), 1) + -0.0728158454836767 + +:func:`~mpmath.stieltjes` supports arbitrary precision evaluation:: + + >>> mp.dps = 50 + >>> stieltjes(2) + -0.0096903631928723184845303860352125293590658061013408 + +**Algorithm** + +:func:`~mpmath.stieltjes` numerically evaluates the integral in +the following representation due to Ainsworth, Howell and +Coffey [1], [2]: + +.. math :: + + \gamma_n(a) = \frac{\log^n a}{2a} - \frac{\log^{n+1}(a)}{n+1} + + \frac{2}{a} \Re \int_0^{\infty} + \frac{(x/a-i)\log^n(a-ix)}{(1+x^2/a^2)(e^{2\pi x}-1)} dx. + +For some reference values with `a = 1`, see e.g. [4]. + +**References** + +1. O. R. Ainsworth & L. W. Howell, "An integral representation of + the generalized Euler-Mascheroni constants", NASA Technical + Paper 2456 (1985), + http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19850014994_1985014994.pdf + +2. M. W. Coffey, "The Stieltjes constants, their relation to the + `\eta_j` coefficients, and representation of the Hurwitz + zeta function", arXiv:0706.0343v1 http://arxiv.org/abs/0706.0343 + +3. http://mathworld.wolfram.com/StieltjesConstants.html + +4. http://pi.lacim.uqam.ca/piDATA/stieltjesgamma.txt + +""" + +gammaprod = r""" +Given iterables `a` and `b`, ``gammaprod(a, b)`` computes the +product / quotient of gamma functions: + +.. math :: + + \frac{\Gamma(a_0) \Gamma(a_1) \cdots \Gamma(a_p)} + {\Gamma(b_0) \Gamma(b_1) \cdots \Gamma(b_q)} + +Unlike direct calls to :func:`~mpmath.gamma`, :func:`~mpmath.gammaprod` considers +the entire product as a limit and evaluates this limit properly if +any of the numerator or denominator arguments are nonpositive +integers such that poles of the gamma function are encountered. +That is, :func:`~mpmath.gammaprod` evaluates + +.. math :: + + \lim_{\epsilon \to 0} + \frac{\Gamma(a_0+\epsilon) \Gamma(a_1+\epsilon) \cdots + \Gamma(a_p+\epsilon)} + {\Gamma(b_0+\epsilon) \Gamma(b_1+\epsilon) \cdots + \Gamma(b_q+\epsilon)} + +In particular: + +* If there are equally many poles in the numerator and the + denominator, the limit is a rational number times the remaining, + regular part of the product. + +* If there are more poles in the numerator, :func:`~mpmath.gammaprod` + returns ``+inf``. + +* If there are more poles in the denominator, :func:`~mpmath.gammaprod` + returns 0. + +**Examples** + +The reciprocal gamma function `1/\Gamma(x)` evaluated at `x = 0`:: + + >>> from mpmath import * + >>> mp.dps = 15 + >>> gammaprod([], [0]) + 0.0 + +A limit:: + + >>> gammaprod([-4], [-3]) + -0.25 + >>> limit(lambda x: gamma(x-1)/gamma(x), -3, direction=1) + -0.25 + >>> limit(lambda x: gamma(x-1)/gamma(x), -3, direction=-1) + -0.25 + +""" + +beta = r""" +Computes the beta function, +`B(x,y) = \Gamma(x) \Gamma(y) / \Gamma(x+y)`. +The beta function is also commonly defined by the integral +representation + +.. math :: + + B(x,y) = \int_0^1 t^{x-1} (1-t)^{y-1} \, dt + +**Examples** + +For integer and half-integer arguments where all three gamma +functions are finite, the beta function becomes either rational +number or a rational multiple of `\pi`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> beta(5, 2) + 0.0333333333333333 + >>> beta(1.5, 2) + 0.266666666666667 + >>> 16*beta(2.5, 1.5) + 3.14159265358979 + +Where appropriate, :func:`~mpmath.beta` evaluates limits. A pole +of the beta function is taken to result in ``+inf``:: + + >>> beta(-0.5, 0.5) + 0.0 + >>> beta(-3, 3) + -0.333333333333333 + >>> beta(-2, 3) + +inf + >>> beta(inf, 1) + 0.0 + >>> beta(inf, 0) + nan + +:func:`~mpmath.beta` supports complex numbers and arbitrary precision +evaluation:: + + >>> beta(1, 2+j) + (0.4 - 0.2j) + >>> mp.dps = 25 + >>> beta(j,0.5) + (1.079424249270925780135675 - 1.410032405664160838288752j) + >>> mp.dps = 50 + >>> beta(pi, e) + 0.037890298781212201348153837138927165984170287886464 + +Various integrals can be computed by means of the +beta function:: + + >>> mp.dps = 15 + >>> quad(lambda t: t**2.5*(1-t)**2, [0, 1]) + 0.0230880230880231 + >>> beta(3.5, 3) + 0.0230880230880231 + >>> quad(lambda t: sin(t)**4 * sqrt(cos(t)), [0, pi/2]) + 0.319504062596158 + >>> beta(2.5, 0.75)/2 + 0.319504062596158 + +""" + +betainc = r""" +``betainc(a, b, x1=0, x2=1, regularized=False)`` gives the generalized +incomplete beta function, + +.. math :: + + I_{x_1}^{x_2}(a,b) = \int_{x_1}^{x_2} t^{a-1} (1-t)^{b-1} dt. + +When `x_1 = 0, x_2 = 1`, this reduces to the ordinary (complete) +beta function `B(a,b)`; see :func:`~mpmath.beta`. + +With the keyword argument ``regularized=True``, :func:`~mpmath.betainc` +computes the regularized incomplete beta function +`I_{x_1}^{x_2}(a,b) / B(a,b)`. This is the cumulative distribution of the +beta distribution with parameters `a`, `b`. + +.. note : + + Implementations of the incomplete beta function in some other + software uses a different argument order. For example, Mathematica uses the + reversed argument order ``Beta[x1,x2,a,b]``. For the equivalent of SciPy's + three-argument incomplete beta integral (implicitly with `x1 = 0`), use + ``betainc(a,b,0,x2,regularized=True)``. + +**Examples** + +Verifying that :func:`~mpmath.betainc` computes the integral in the +definition:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> x,y,a,b = 3, 4, 0, 6 + >>> betainc(x, y, a, b) + -4010.4 + >>> quad(lambda t: t**(x-1) * (1-t)**(y-1), [a, b]) + -4010.4 + +The arguments may be arbitrary complex numbers:: + + >>> betainc(0.75, 1-4j, 0, 2+3j) + (0.2241657956955709603655887 + 0.3619619242700451992411724j) + +With regularization:: + + >>> betainc(1, 2, 0, 0.25, regularized=True) + 0.4375 + >>> betainc(pi, e, 0, 1, regularized=True) # Complete + 1.0 + +The beta integral satisfies some simple argument transformation +symmetries:: + + >>> mp.dps = 15 + >>> betainc(2,3,4,5), -betainc(2,3,5,4), betainc(3,2,1-5,1-4) + (56.0833333333333, 56.0833333333333, 56.0833333333333) + +The beta integral can often be evaluated analytically. For integer and +rational arguments, the incomplete beta function typically reduces to a +simple algebraic-logarithmic expression:: + + >>> mp.dps = 25 + >>> identify(chop(betainc(0, 0, 3, 4))) + '-(log((9/8)))' + >>> identify(betainc(2, 3, 4, 5)) + '(673/12)' + >>> identify(betainc(1.5, 1, 1, 2)) + '((-12+sqrt(1152))/18)' + +""" + +binomial = r""" +Computes the binomial coefficient + +.. math :: + + {n \choose k} = \frac{n!}{k!(n-k)!}. + +The binomial coefficient gives the number of ways that `k` items +can be chosen from a set of `n` items. More generally, the binomial +coefficient is a well-defined function of arbitrary real or +complex `n` and `k`, via the gamma function. + +**Examples** + +Generate Pascal's triangle:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(5): + ... nprint([binomial(n,k) for k in range(n+1)]) + ... + [1.0] + [1.0, 1.0] + [1.0, 2.0, 1.0] + [1.0, 3.0, 3.0, 1.0] + [1.0, 4.0, 6.0, 4.0, 1.0] + +There is 1 way to select 0 items from the empty set, and 0 ways to +select 1 item from the empty set:: + + >>> binomial(0, 0) + 1.0 + >>> binomial(0, 1) + 0.0 + +:func:`~mpmath.binomial` supports large arguments:: + + >>> binomial(10**20, 10**20-5) + 8.33333333333333e+97 + >>> binomial(10**20, 10**10) + 2.60784095465201e+104342944813 + +Nonintegral binomial coefficients find use in series +expansions:: + + >>> nprint(taylor(lambda x: (1+x)**0.25, 0, 4)) + [1.0, 0.25, -0.09375, 0.0546875, -0.0375977] + >>> nprint([binomial(0.25, k) for k in range(5)]) + [1.0, 0.25, -0.09375, 0.0546875, -0.0375977] + +An integral representation:: + + >>> n, k = 5, 3 + >>> f = lambda t: exp(-j*k*t)*(1+exp(j*t))**n + >>> chop(quad(f, [-pi,pi])/(2*pi)) + 10.0 + >>> binomial(n,k) + 10.0 + +""" + +rf = r""" +Computes the rising factorial or Pochhammer symbol, + +.. math :: + + x^{(n)} = x (x+1) \cdots (x+n-1) = \frac{\Gamma(x+n)}{\Gamma(x)} + +where the rightmost expression is valid for nonintegral `n`. + +**Examples** + +For integral `n`, the rising factorial is a polynomial:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(5): + ... nprint(taylor(lambda x: rf(x,n), 0, n)) + ... + [1.0] + [0.0, 1.0] + [0.0, 1.0, 1.0] + [0.0, 2.0, 3.0, 1.0] + [0.0, 6.0, 11.0, 6.0, 1.0] + +Evaluation is supported for arbitrary arguments:: + + >>> rf(2+3j, 5.5) + (-7202.03920483347 - 3777.58810701527j) +""" + +ff = r""" +Computes the falling factorial, + +.. math :: + + (x)_n = x (x-1) \cdots (x-n+1) = \frac{\Gamma(x+1)}{\Gamma(x-n+1)} + +where the rightmost expression is valid for nonintegral `n`. + +**Examples** + +For integral `n`, the falling factorial is a polynomial:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(5): + ... nprint(taylor(lambda x: ff(x,n), 0, n)) + ... + [1.0] + [0.0, 1.0] + [0.0, -1.0, 1.0] + [0.0, 2.0, -3.0, 1.0] + [0.0, -6.0, 11.0, -6.0, 1.0] + +Evaluation is supported for arbitrary arguments:: + + >>> ff(2+3j, 5.5) + (-720.41085888203 + 316.101124983878j) +""" + +fac2 = r""" +Computes the double factorial `x!!`, defined for integers +`x > 0` by + +.. math :: + + x!! = \begin{cases} + 1 \cdot 3 \cdots (x-2) \cdot x & x \;\mathrm{odd} \\ + 2 \cdot 4 \cdots (x-2) \cdot x & x \;\mathrm{even} + \end{cases} + +and more generally by [1] + +.. math :: + + x!! = 2^{x/2} \left(\frac{\pi}{2}\right)^{(\cos(\pi x)-1)/4} + \Gamma\left(\frac{x}{2}+1\right). + +**Examples** + +The integer sequence of double factorials begins:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> nprint([fac2(n) for n in range(10)]) + [1.0, 1.0, 2.0, 3.0, 8.0, 15.0, 48.0, 105.0, 384.0, 945.0] + +For large `x`, double factorials follow a Stirling-like asymptotic +approximation:: + + >>> x = mpf(10000) + >>> fac2(x) + 5.97272691416282e+17830 + >>> sqrt(pi)*x**((x+1)/2)*exp(-x/2) + 5.97262736954392e+17830 + +The recurrence formula `x!! = x (x-2)!!` can be reversed to +define the double factorial of negative odd integers (but +not negative even integers):: + + >>> fac2(-1), fac2(-3), fac2(-5), fac2(-7) + (1.0, -1.0, 0.333333333333333, -0.0666666666666667) + >>> fac2(-2) + Traceback (most recent call last): + ... + ValueError: gamma function pole + +With the exception of the poles at negative even integers, +:func:`~mpmath.fac2` supports evaluation for arbitrary complex arguments. +The recurrence formula is valid generally:: + + >>> fac2(pi+2j) + (-1.3697207890154e-12 + 3.93665300979176e-12j) + >>> (pi+2j)*fac2(pi-2+2j) + (-1.3697207890154e-12 + 3.93665300979176e-12j) + +Double factorials should not be confused with nested factorials, +which are immensely larger:: + + >>> fac(fac(20)) + 5.13805976125208e+43675043585825292774 + >>> fac2(20) + 3715891200.0 + +Double factorials appear, among other things, in series expansions +of Gaussian functions and the error function. Infinite series +include:: + + >>> nsum(lambda k: 1/fac2(k), [0, inf]) + 3.05940740534258 + >>> sqrt(e)*(1+sqrt(pi/2)*erf(sqrt(2)/2)) + 3.05940740534258 + >>> nsum(lambda k: 2**k/fac2(2*k-1), [1, inf]) + 4.06015693855741 + >>> e * erf(1) * sqrt(pi) + 4.06015693855741 + +A beautiful Ramanujan sum:: + + >>> nsum(lambda k: (-1)**k*(fac2(2*k-1)/fac2(2*k))**3, [0,inf]) + 0.90917279454693 + >>> (gamma('9/8')/gamma('5/4')/gamma('7/8'))**2 + 0.90917279454693 + +**References** + +1. http://functions.wolfram.com/GammaBetaErf/Factorial2/27/01/0002/ + +2. http://mathworld.wolfram.com/DoubleFactorial.html + +""" + +hyper = r""" +Evaluates the generalized hypergeometric function + +.. math :: + + \,_pF_q(a_1,\ldots,a_p; b_1,\ldots,b_q; z) = + \sum_{n=0}^\infty \frac{(a_1)_n (a_2)_n \ldots (a_p)_n} + {(b_1)_n(b_2)_n\ldots(b_q)_n} \frac{z^n}{n!} + +where `(x)_n` denotes the rising factorial (see :func:`~mpmath.rf`). + +The parameters lists ``a_s`` and ``b_s`` may contain integers, +real numbers, complex numbers, as well as exact fractions given in +the form of tuples `(p, q)`. :func:`~mpmath.hyper` is optimized to handle +integers and fractions more efficiently than arbitrary +floating-point parameters (since rational parameters are by +far the most common). + +**Examples** + +Verifying that :func:`~mpmath.hyper` gives the sum in the definition, by +comparison with :func:`~mpmath.nsum`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> a,b,c,d = 2,3,4,5 + >>> x = 0.25 + >>> hyper([a,b],[c,d],x) + 1.078903941164934876086237 + >>> fn = lambda n: rf(a,n)*rf(b,n)/rf(c,n)/rf(d,n)*x**n/fac(n) + >>> nsum(fn, [0, inf]) + 1.078903941164934876086237 + +The parameters can be any combination of integers, fractions, +floats and complex numbers:: + + >>> a, b, c, d, e = 1, (-1,2), pi, 3+4j, (2,3) + >>> x = 0.2j + >>> hyper([a,b],[c,d,e],x) + (0.9923571616434024810831887 - 0.005753848733883879742993122j) + >>> b, e = -0.5, mpf(2)/3 + >>> fn = lambda n: rf(a,n)*rf(b,n)/rf(c,n)/rf(d,n)/rf(e,n)*x**n/fac(n) + >>> nsum(fn, [0, inf]) + (0.9923571616434024810831887 - 0.005753848733883879742993122j) + +The `\,_0F_0` and `\,_1F_0` series are just elementary functions:: + + >>> a, z = sqrt(2), +pi + >>> hyper([],[],z) + 23.14069263277926900572909 + >>> exp(z) + 23.14069263277926900572909 + >>> hyper([a],[],z) + (-0.09069132879922920160334114 + 0.3283224323946162083579656j) + >>> (1-z)**(-a) + (-0.09069132879922920160334114 + 0.3283224323946162083579656j) + +If any `a_k` coefficient is a nonpositive integer, the series terminates +into a finite polynomial:: + + >>> hyper([1,1,1,-3],[2,5],1) + 0.7904761904761904761904762 + >>> identify(_) + '(83/105)' + +If any `b_k` is a nonpositive integer, the function is undefined (unless the +series terminates before the division by zero occurs):: + + >>> hyper([1,1,1,-3],[-2,5],1) + Traceback (most recent call last): + ... + ZeroDivisionError: pole in hypergeometric series + >>> hyper([1,1,1,-1],[-2,5],1) + 1.1 + +Except for polynomial cases, the radius of convergence `R` of the hypergeometric +series is either `R = \infty` (if `p \le q`), `R = 1` (if `p = q+1`), or +`R = 0` (if `p > q+1`). + +The analytic continuations of the functions with `p = q+1`, i.e. `\,_2F_1`, +`\,_3F_2`, `\,_4F_3`, etc, are all implemented and therefore these functions +can be evaluated for `|z| \ge 1`. The shortcuts :func:`~mpmath.hyp2f1`, :func:`~mpmath.hyp3f2` +are available to handle the most common cases (see their documentation), +but functions of higher degree are also supported via :func:`~mpmath.hyper`:: + + >>> hyper([1,2,3,4], [5,6,7], 1) # 4F3 at finite-valued branch point + 1.141783505526870731311423 + >>> hyper([4,5,6,7], [1,2,3], 1) # 4F3 at pole + +inf + >>> hyper([1,2,3,4,5], [6,7,8,9], 10) # 5F4 + (1.543998916527972259717257 - 0.5876309929580408028816365j) + >>> hyper([1,2,3,4,5,6], [7,8,9,10,11], 1j) # 6F5 + (0.9996565821853579063502466 + 0.0129721075905630604445669j) + +Near `z = 1` with noninteger parameters:: + + >>> hyper(['1/3',1,'3/2',2], ['1/5','11/6','41/8'], 1) + 2.219433352235586121250027 + >>> hyper(['1/3',1,'3/2',2], ['1/5','11/6','5/4'], 1) + +inf + >>> eps1 = extradps(6)(lambda: 1 - mpf('1e-6'))() + >>> hyper(['1/3',1,'3/2',2], ['1/5','11/6','5/4'], eps1) + 2923978034.412973409330956 + +Please note that, as currently implemented, evaluation of `\,_pF_{p-1}` +with `p \ge 3` may be slow or inaccurate when `|z-1|` is small, +for some parameter values. + +Evaluation may be aborted if convergence appears to be too slow. +The optional ``maxterms`` (limiting the number of series terms) and ``maxprec`` +(limiting the internal precision) keyword arguments can be used +to control evaluation:: + + >>> hyper([1,2,3], [4,5,6], 10000) # doctest: +IGNORE_EXCEPTION_DETAIL + Traceback (most recent call last): + ... + NoConvergence: Hypergeometric series converges too slowly. Try increasing maxterms. + >>> hyper([1,2,3], [4,5,6], 10000, maxterms=10**6) + 7.622806053177969474396918e+4310 + +Additional options include ``force_series`` (which forces direct use of +a hypergeometric series even if another evaluation method might work better) +and ``asymp_tol`` which controls the target tolerance for using +asymptotic series. + +When `p > q+1`, ``hyper`` computes the (iterated) Borel sum of the divergent +series. For `\,_2F_0` the Borel sum has an analytic solution and can be +computed efficiently (see :func:`~mpmath.hyp2f0`). For higher degrees, the functions +is evaluated first by attempting to sum it directly as an asymptotic +series (this only works for tiny `|z|`), and then by evaluating the Borel +regularized sum using numerical integration. Except for +special parameter combinations, this can be extremely slow. + + >>> hyper([1,1], [], 0.5) # regularization of 2F0 + (1.340965419580146562086448 + 0.8503366631752726568782447j) + >>> hyper([1,1,1,1], [1], 0.5) # regularization of 4F1 + (1.108287213689475145830699 + 0.5327107430640678181200491j) + +With the following magnitude of argument, the asymptotic series for `\,_3F_1` +gives only a few digits. Using Borel summation, ``hyper`` can produce +a value with full accuracy:: + + >>> mp.dps = 15 + >>> hyper([2,0.5,4], [5.25], '0.08', force_series=True) # doctest: +IGNORE_EXCEPTION_DETAIL + Traceback (most recent call last): + ... + NoConvergence: Hypergeometric series converges too slowly. Try increasing maxterms. + >>> hyper([2,0.5,4], [5.25], '0.08', asymp_tol=1e-4) + 1.0725535790737 + >>> hyper([2,0.5,4], [5.25], '0.08') + (1.07269542893559 + 5.54668863216891e-5j) + >>> hyper([2,0.5,4], [5.25], '-0.08', asymp_tol=1e-4) + 0.946344925484879 + >>> hyper([2,0.5,4], [5.25], '-0.08') + 0.946312503737771 + >>> mp.dps = 25 + >>> hyper([2,0.5,4], [5.25], '-0.08') + 0.9463125037377662296700858 + +Note that with the positive `z` value, there is a complex part in the +correct result, which falls below the tolerance of the asymptotic series. + +By default, a parameter that appears in both ``a_s`` and ``b_s`` will be removed +unless it is a nonpositive integer. This generally speeds up evaluation +by producing a hypergeometric function of lower order. +This optimization can be disabled by passing ``eliminate=False``. + + >>> hyper([1,2,3], [4,5,3], 10000) + 1.268943190440206905892212e+4321 + >>> hyper([1,2,3], [4,5,3], 10000, eliminate=False) # doctest: +IGNORE_EXCEPTION_DETAIL + Traceback (most recent call last): + ... + NoConvergence: Hypergeometric series converges too slowly. Try increasing maxterms. + >>> hyper([1,2,3], [4,5,3], 10000, eliminate=False, maxterms=10**6) + 1.268943190440206905892212e+4321 + +If a nonpositive integer `-n` appears in both ``a_s`` and ``b_s``, this parameter +cannot be unambiguously removed since it creates a term 0 / 0. +In this case the hypergeometric series is understood to terminate before +the division by zero occurs. This convention is consistent with Mathematica. +An alternative convention of eliminating the parameters can be toggled +with ``eliminate_all=True``: + + >>> hyper([2,-1], [-1], 3) + 7.0 + >>> hyper([2,-1], [-1], 3, eliminate_all=True) + 0.25 + >>> hyper([2], [], 3) + 0.25 + +""" + +hypercomb = r""" +Computes a weighted combination of hypergeometric functions + +.. math :: + + \sum_{r=1}^N \left[ \prod_{k=1}^{l_r} {w_{r,k}}^{c_{r,k}} + \frac{\prod_{k=1}^{m_r} \Gamma(\alpha_{r,k})}{\prod_{k=1}^{n_r} + \Gamma(\beta_{r,k})} + \,_{p_r}F_{q_r}(a_{r,1},\ldots,a_{r,p}; b_{r,1}, + \ldots, b_{r,q}; z_r)\right]. + +Typically the parameters are linear combinations of a small set of base +parameters; :func:`~mpmath.hypercomb` permits computing a correct value in +the case that some of the `\alpha`, `\beta`, `b` turn out to be +nonpositive integers, or if division by zero occurs for some `w^c`, +assuming that there are opposing singularities that cancel out. +The limit is computed by evaluating the function with the base +parameters perturbed, at a higher working precision. + +The first argument should be a function that takes the perturbable +base parameters ``params`` as input and returns `N` tuples +``(w, c, alpha, beta, a, b, z)``, where the coefficients ``w``, ``c``, +gamma factors ``alpha``, ``beta``, and hypergeometric coefficients +``a``, ``b`` each should be lists of numbers, and ``z`` should be a single +number. + +**Examples** + +The following evaluates + +.. math :: + + (a-1) \frac{\Gamma(a-3)}{\Gamma(a-4)} \,_1F_1(a,a-1,z) = e^z(a-4)(a+z-1) + +with `a=1, z=3`. There is a zero factor, two gamma function poles, and +the 1F1 function is singular; all singularities cancel out to give a finite +value:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> hypercomb(lambda a: [([a-1],[1],[a-3],[a-4],[a],[a-1],3)], [1]) + -180.769832308689 + >>> -9*exp(3) + -180.769832308689 + +""" + +hyp0f1 = r""" +Gives the hypergeometric function `\,_0F_1`, sometimes known as the +confluent limit function, defined as + +.. math :: + + \,_0F_1(a,z) = \sum_{k=0}^{\infty} \frac{1}{(a)_k} \frac{z^k}{k!}. + +This function satisfies the differential equation `z f''(z) + a f'(z) = f(z)`, +and is related to the Bessel function of the first kind (see :func:`~mpmath.besselj`). + +``hyp0f1(a,z)`` is equivalent to ``hyper([],[a],z)``; see documentation for +:func:`~mpmath.hyper` for more information. + +**Examples** + +Evaluation for arbitrary arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyp0f1(2, 0.25) + 1.130318207984970054415392 + >>> hyp0f1((1,2), 1234567) + 6.27287187546220705604627e+964 + >>> hyp0f1(3+4j, 1000000j) + (3.905169561300910030267132e+606 + 3.807708544441684513934213e+606j) + +Evaluation is supported for arbitrarily large values of `z`, +using asymptotic expansions:: + + >>> hyp0f1(1, 10**50) + 2.131705322874965310390701e+8685889638065036553022565 + >>> hyp0f1(1, -10**50) + 1.115945364792025420300208e-13 + +Verifying the differential equation:: + + >>> a = 2.5 + >>> f = lambda z: hyp0f1(a,z) + >>> for z in [0, 10, 3+4j]: + ... chop(z*diff(f,z,2) + a*diff(f,z) - f(z)) + ... + 0.0 + 0.0 + 0.0 + +""" + +hyp1f1 = r""" +Gives the confluent hypergeometric function of the first kind, + +.. math :: + + \,_1F_1(a,b,z) = \sum_{k=0}^{\infty} \frac{(a)_k}{(b)_k} \frac{z^k}{k!}, + +also known as Kummer's function and sometimes denoted by `M(a,b,z)`. This +function gives one solution to the confluent (Kummer's) differential equation + +.. math :: + + z f''(z) + (b-z) f'(z) - af(z) = 0. + +A second solution is given by the `U` function; see :func:`~mpmath.hyperu`. +Solutions are also given in an alternate form by the Whittaker +functions (:func:`~mpmath.whitm`, :func:`~mpmath.whitw`). + +``hyp1f1(a,b,z)`` is equivalent +to ``hyper([a],[b],z)``; see documentation for :func:`~mpmath.hyper` for more +information. + +**Examples** + +Evaluation for real and complex values of the argument `z`, with +fixed parameters `a = 2, b = -1/3`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyp1f1(2, (-1,3), 3.25) + -2815.956856924817275640248 + >>> hyp1f1(2, (-1,3), -3.25) + -1.145036502407444445553107 + >>> hyp1f1(2, (-1,3), 1000) + -8.021799872770764149793693e+441 + >>> hyp1f1(2, (-1,3), -1000) + 0.000003131987633006813594535331 + >>> hyp1f1(2, (-1,3), 100+100j) + (-3.189190365227034385898282e+48 - 1.106169926814270418999315e+49j) + +Parameters may be complex:: + + >>> hyp1f1(2+3j, -1+j, 10j) + (261.8977905181045142673351 + 160.8930312845682213562172j) + +Arbitrarily large values of `z` are supported:: + + >>> hyp1f1(3, 4, 10**20) + 3.890569218254486878220752e+43429448190325182745 + >>> hyp1f1(3, 4, -10**20) + 6.0e-60 + >>> hyp1f1(3, 4, 10**20*j) + (-1.935753855797342532571597e-20 - 2.291911213325184901239155e-20j) + +Verifying the differential equation:: + + >>> a, b = 1.5, 2 + >>> f = lambda z: hyp1f1(a,b,z) + >>> for z in [0, -10, 3, 3+4j]: + ... chop(z*diff(f,z,2) + (b-z)*diff(f,z) - a*f(z)) + ... + 0.0 + 0.0 + 0.0 + 0.0 + +An integral representation:: + + >>> a, b = 1.5, 3 + >>> z = 1.5 + >>> hyp1f1(a,b,z) + 2.269381460919952778587441 + >>> g = lambda t: exp(z*t)*t**(a-1)*(1-t)**(b-a-1) + >>> gammaprod([b],[a,b-a])*quad(g, [0,1]) + 2.269381460919952778587441 + + +""" + +hyp1f2 = r""" +Gives the hypergeometric function `\,_1F_2(a_1,a_2;b_1,b_2; z)`. +The call ``hyp1f2(a1,b1,b2,z)`` is equivalent to +``hyper([a1],[b1,b2],z)``. + +Evaluation works for complex and arbitrarily large arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> a, b, c = 1.5, (-1,3), 2.25 + >>> hyp1f2(a, b, c, 10**20) + -1.159388148811981535941434e+8685889639 + >>> hyp1f2(a, b, c, -10**20) + -12.60262607892655945795907 + >>> hyp1f2(a, b, c, 10**20*j) + (4.237220401382240876065501e+6141851464 - 2.950930337531768015892987e+6141851464j) + >>> hyp1f2(2+3j, -2j, 0.5j, 10-20j) + (135881.9905586966432662004 - 86681.95885418079535738828j) + +""" + +hyp2f2 = r""" +Gives the hypergeometric function `\,_2F_2(a_1,a_2;b_1,b_2; z)`. +The call ``hyp2f2(a1,a2,b1,b2,z)`` is equivalent to +``hyper([a1,a2],[b1,b2],z)``. + +Evaluation works for complex and arbitrarily large arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> a, b, c, d = 1.5, (-1,3), 2.25, 4 + >>> hyp2f2(a, b, c, d, 10**20) + -5.275758229007902299823821e+43429448190325182663 + >>> hyp2f2(a, b, c, d, -10**20) + 2561445.079983207701073448 + >>> hyp2f2(a, b, c, d, 10**20*j) + (2218276.509664121194836667 - 1280722.539991603850462856j) + >>> hyp2f2(2+3j, -2j, 0.5j, 4j, 10-20j) + (80500.68321405666957342788 - 20346.82752982813540993502j) + +""" + +hyp2f3 = r""" +Gives the hypergeometric function `\,_2F_3(a_1,a_2;b_1,b_2,b_3; z)`. +The call ``hyp2f3(a1,a2,b1,b2,b3,z)`` is equivalent to +``hyper([a1,a2],[b1,b2,b3],z)``. + +Evaluation works for arbitrarily large arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> a1,a2,b1,b2,b3 = 1.5, (-1,3), 2.25, 4, (1,5) + >>> hyp2f3(a1,a2,b1,b2,b3,10**20) + -4.169178177065714963568963e+8685889590 + >>> hyp2f3(a1,a2,b1,b2,b3,-10**20) + 7064472.587757755088178629 + >>> hyp2f3(a1,a2,b1,b2,b3,10**20*j) + (-5.163368465314934589818543e+6141851415 + 1.783578125755972803440364e+6141851416j) + >>> hyp2f3(2+3j, -2j, 0.5j, 4j, -1-j, 10-20j) + (-2280.938956687033150740228 + 13620.97336609573659199632j) + >>> hyp2f3(2+3j, -2j, 0.5j, 4j, -1-j, 10000000-20000000j) + (4.849835186175096516193e+3504 - 3.365981529122220091353633e+3504j) + +""" + +hyp2f1 = r""" +Gives the Gauss hypergeometric function `\,_2F_1` (often simply referred to as +*the* hypergeometric function), defined for `|z| < 1` as + +.. math :: + + \,_2F_1(a,b,c,z) = \sum_{k=0}^{\infty} + \frac{(a)_k (b)_k}{(c)_k} \frac{z^k}{k!}. + +and for `|z| \ge 1` by analytic continuation, with a branch cut on `(1, \infty)` +when necessary. + +Special cases of this function include many of the orthogonal polynomials as +well as the incomplete beta function and other functions. Properties of the +Gauss hypergeometric function are documented comprehensively in many references, +for example Abramowitz & Stegun, section 15. + +The implementation supports the analytic continuation as well as evaluation +close to the unit circle where `|z| \approx 1`. The syntax ``hyp2f1(a,b,c,z)`` +is equivalent to ``hyper([a,b],[c],z)``. + +**Examples** + +Evaluation with `z` inside, outside and on the unit circle, for +fixed parameters:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyp2f1(2, (1,2), 4, 0.75) + 1.303703703703703703703704 + >>> hyp2f1(2, (1,2), 4, -1.75) + 0.7431290566046919177853916 + >>> hyp2f1(2, (1,2), 4, 1.75) + (1.418075801749271137026239 - 1.114976146679907015775102j) + >>> hyp2f1(2, (1,2), 4, 1) + 1.6 + >>> hyp2f1(2, (1,2), 4, -1) + 0.8235498012182875315037882 + >>> hyp2f1(2, (1,2), 4, j) + (0.9144026291433065674259078 + 0.2050415770437884900574923j) + >>> hyp2f1(2, (1,2), 4, 2+j) + (0.9274013540258103029011549 + 0.7455257875808100868984496j) + >>> hyp2f1(2, (1,2), 4, 0.25j) + (0.9931169055799728251931672 + 0.06154836525312066938147793j) + +Evaluation with complex parameter values:: + + >>> hyp2f1(1+j, 0.75, 10j, 1+5j) + (0.8834833319713479923389638 + 0.7053886880648105068343509j) + +Evaluation with `z = 1`:: + + >>> hyp2f1(-2.5, 3.5, 1.5, 1) + 0.0 + >>> hyp2f1(-2.5, 3, 4, 1) + 0.06926406926406926406926407 + >>> hyp2f1(2, 3, 4, 1) + +inf + +Evaluation for huge arguments:: + + >>> hyp2f1((-1,3), 1.75, 4, '1e100') + (7.883714220959876246415651e+32 + 1.365499358305579597618785e+33j) + >>> hyp2f1((-1,3), 1.75, 4, '1e1000000') + (7.883714220959876246415651e+333332 + 1.365499358305579597618785e+333333j) + >>> hyp2f1((-1,3), 1.75, 4, '1e1000000j') + (1.365499358305579597618785e+333333 - 7.883714220959876246415651e+333332j) + +An integral representation:: + + >>> a,b,c,z = -0.5, 1, 2.5, 0.25 + >>> g = lambda t: t**(b-1) * (1-t)**(c-b-1) * (1-t*z)**(-a) + >>> gammaprod([c],[b,c-b]) * quad(g, [0,1]) + 0.9480458814362824478852618 + >>> hyp2f1(a,b,c,z) + 0.9480458814362824478852618 + +Verifying the hypergeometric differential equation:: + + >>> f = lambda z: hyp2f1(a,b,c,z) + >>> chop(z*(1-z)*diff(f,z,2) + (c-(a+b+1)*z)*diff(f,z) - a*b*f(z)) + 0.0 + +""" + +hyp3f2 = r""" +Gives the generalized hypergeometric function `\,_3F_2`, defined for `|z| < 1` +as + +.. math :: + + \,_3F_2(a_1,a_2,a_3,b_1,b_2,z) = \sum_{k=0}^{\infty} + \frac{(a_1)_k (a_2)_k (a_3)_k}{(b_1)_k (b_2)_k} \frac{z^k}{k!}. + +and for `|z| \ge 1` by analytic continuation. The analytic structure of this +function is similar to that of `\,_2F_1`, generally with a singularity at +`z = 1` and a branch cut on `(1, \infty)`. + +Evaluation is supported inside, on, and outside +the circle of convergence `|z| = 1`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyp3f2(1,2,3,4,5,0.25) + 1.083533123380934241548707 + >>> hyp3f2(1,2+2j,3,4,5,-10+10j) + (0.1574651066006004632914361 - 0.03194209021885226400892963j) + >>> hyp3f2(1,2,3,4,5,-10) + 0.3071141169208772603266489 + >>> hyp3f2(1,2,3,4,5,10) + (-0.4857045320523947050581423 - 0.5988311440454888436888028j) + >>> hyp3f2(0.25,1,1,2,1.5,1) + 1.157370995096772047567631 + >>> (8-pi-2*ln2)/3 + 1.157370995096772047567631 + >>> hyp3f2(1+j,0.5j,2,1,-2j,-1) + (1.74518490615029486475959 + 0.1454701525056682297614029j) + >>> hyp3f2(1+j,0.5j,2,1,-2j,sqrt(j)) + (0.9829816481834277511138055 - 0.4059040020276937085081127j) + >>> hyp3f2(-3,2,1,-5,4,1) + 1.41 + >>> hyp3f2(-3,2,1,-5,4,2) + 2.12 + +Evaluation very close to the unit circle:: + + >>> hyp3f2(1,2,3,4,5,'1.0001') + (1.564877796743282766872279 - 3.76821518787438186031973e-11j) + >>> hyp3f2(1,2,3,4,5,'1+0.0001j') + (1.564747153061671573212831 + 0.0001305757570366084557648482j) + >>> hyp3f2(1,2,3,4,5,'0.9999') + 1.564616644881686134983664 + >>> hyp3f2(1,2,3,4,5,'-0.9999') + 0.7823896253461678060196207 + +.. note :: + + Evaluation for `|z-1|` small can currently be inaccurate or slow + for some parameter combinations. + +For various parameter combinations, `\,_3F_2` admits representation in terms +of hypergeometric functions of lower degree, or in terms of +simpler functions:: + + >>> for a, b, z in [(1,2,-1), (2,0.5,1)]: + ... hyp2f1(a,b,a+b+0.5,z)**2 + ... hyp3f2(2*a,a+b,2*b,a+b+0.5,2*a+2*b,z) + ... + 0.4246104461966439006086308 + 0.4246104461966439006086308 + 7.111111111111111111111111 + 7.111111111111111111111111 + + >>> z = 2+3j + >>> hyp3f2(0.5,1,1.5,2,2,z) + (0.7621440939243342419729144 + 0.4249117735058037649915723j) + >>> 4*(pi-2*ellipe(z))/(pi*z) + (0.7621440939243342419729144 + 0.4249117735058037649915723j) + +""" + +hyperu = r""" +Gives the Tricomi confluent hypergeometric function `U`, also known as +the Kummer or confluent hypergeometric function of the second kind. This +function gives a second linearly independent solution to the confluent +hypergeometric differential equation (the first is provided by `\,_1F_1` -- +see :func:`~mpmath.hyp1f1`). + +**Examples** + +Evaluation for arbitrary complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyperu(2,3,4) + 0.0625 + >>> hyperu(0.25, 5, 1000) + 0.1779949416140579573763523 + >>> hyperu(0.25, 5, -1000) + (0.1256256609322773150118907 - 0.1256256609322773150118907j) + +The `U` function may be singular at `z = 0`:: + + >>> hyperu(1.5, 2, 0) + +inf + >>> hyperu(1.5, -2, 0) + 0.1719434921288400112603671 + +Verifying the differential equation:: + + >>> a, b = 1.5, 2 + >>> f = lambda z: hyperu(a,b,z) + >>> for z in [-10, 3, 3+4j]: + ... chop(z*diff(f,z,2) + (b-z)*diff(f,z) - a*f(z)) + ... + 0.0 + 0.0 + 0.0 + +An integral representation:: + + >>> a,b,z = 2, 3.5, 4.25 + >>> hyperu(a,b,z) + 0.06674960718150520648014567 + >>> quad(lambda t: exp(-z*t)*t**(a-1)*(1+t)**(b-a-1),[0,inf]) / gamma(a) + 0.06674960718150520648014567 + + +[1] http://people.math.sfu.ca/~cbm/aands/page_504.htm +""" + +hyp2f0 = r""" +Gives the hypergeometric function `\,_2F_0`, defined formally by the +series + +.. math :: + + \,_2F_0(a,b;;z) = \sum_{n=0}^{\infty} (a)_n (b)_n \frac{z^n}{n!}. + +This series usually does not converge. For small enough `z`, it can be viewed +as an asymptotic series that may be summed directly with an appropriate +truncation. When this is not the case, :func:`~mpmath.hyp2f0` gives a regularized sum, +or equivalently, it uses a representation in terms of the +hypergeometric U function [1]. The series also converges when either `a` or `b` +is a nonpositive integer, as it then terminates into a polynomial +after `-a` or `-b` terms. + +**Examples** + +Evaluation is supported for arbitrary complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hyp2f0((2,3), 1.25, -100) + 0.07095851870980052763312791 + >>> hyp2f0((2,3), 1.25, 100) + (-0.03254379032170590665041131 + 0.07269254613282301012735797j) + >>> hyp2f0(-0.75, 1-j, 4j) + (-0.3579987031082732264862155 - 3.052951783922142735255881j) + +Even with real arguments, the regularized value of 2F0 is often complex-valued, +but the imaginary part decreases exponentially as `z \to 0`. In the following +example, the first call uses complex evaluation while the second has a small +enough `z` to evaluate using the direct series and thus the returned value +is strictly real (this should be taken to indicate that the imaginary +part is less than ``eps``):: + + >>> mp.dps = 15 + >>> hyp2f0(1.5, 0.5, 0.05) + (1.04166637647907 + 8.34584913683906e-8j) + >>> hyp2f0(1.5, 0.5, 0.0005) + 1.00037535207621 + +The imaginary part can be retrieved by increasing the working precision:: + + >>> mp.dps = 80 + >>> nprint(hyp2f0(1.5, 0.5, 0.009).imag) + 1.23828e-46 + +In the polynomial case (the series terminating), 2F0 can evaluate exactly:: + + >>> mp.dps = 15 + >>> hyp2f0(-6,-6,2) + 291793.0 + >>> identify(hyp2f0(-2,1,0.25)) + '(5/8)' + +The coefficients of the polynomials can be recovered using Taylor expansion:: + + >>> nprint(taylor(lambda x: hyp2f0(-3,0.5,x), 0, 10)) + [1.0, -1.5, 2.25, -1.875, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0] + >>> nprint(taylor(lambda x: hyp2f0(-4,0.5,x), 0, 10)) + [1.0, -2.0, 4.5, -7.5, 6.5625, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0] + + +[1] http://people.math.sfu.ca/~cbm/aands/page_504.htm +""" + + +gammainc = r""" +``gammainc(z, a=0, b=inf)`` computes the (generalized) incomplete +gamma function with integration limits `[a, b]`: + +.. math :: + + \Gamma(z,a,b) = \int_a^b t^{z-1} e^{-t} \, dt + +The generalized incomplete gamma function reduces to the +following special cases when one or both endpoints are fixed: + +* `\Gamma(z,0,\infty)` is the standard ("complete") + gamma function, `\Gamma(z)` (available directly + as the mpmath function :func:`~mpmath.gamma`) +* `\Gamma(z,a,\infty)` is the "upper" incomplete gamma + function, `\Gamma(z,a)` +* `\Gamma(z,0,b)` is the "lower" incomplete gamma + function, `\gamma(z,b)`. + +Of course, we have +`\Gamma(z,0,x) + \Gamma(z,x,\infty) = \Gamma(z)` +for all `z` and `x`. + +Note however that some authors reverse the order of the +arguments when defining the lower and upper incomplete +gamma function, so one should be careful to get the correct +definition. + +If also given the keyword argument ``regularized=True``, +:func:`~mpmath.gammainc` computes the "regularized" incomplete gamma +function + +.. math :: + + P(z,a,b) = \frac{\Gamma(z,a,b)}{\Gamma(z)}. + +**Examples** + +We can compare with numerical quadrature to verify that +:func:`~mpmath.gammainc` computes the integral in the definition:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> gammainc(2+3j, 4, 10) + (0.00977212668627705160602312 - 0.0770637306312989892451977j) + >>> quad(lambda t: t**(2+3j-1) * exp(-t), [4, 10]) + (0.00977212668627705160602312 - 0.0770637306312989892451977j) + +Argument symmetries follow directly from the integral definition:: + + >>> gammainc(3, 4, 5) + gammainc(3, 5, 4) + 0.0 + >>> gammainc(3,0,2) + gammainc(3,2,4); gammainc(3,0,4) + 1.523793388892911312363331 + 1.523793388892911312363331 + >>> findroot(lambda z: gammainc(2,z,3), 1) + 3.0 + +Evaluation for arbitrarily large arguments:: + + >>> gammainc(10, 100) + 4.083660630910611272288592e-26 + >>> gammainc(10, 10000000000000000) + 5.290402449901174752972486e-4342944819032375 + >>> gammainc(3+4j, 1000000+1000000j) + (-1.257913707524362408877881e-434284 + 2.556691003883483531962095e-434284j) + +Evaluation of a generalized incomplete gamma function automatically chooses +the representation that gives a more accurate result, depending on which +parameter is larger:: + + >>> gammainc(10000000, 3) - gammainc(10000000, 2) # Bad + 0.0 + >>> gammainc(10000000, 2, 3) # Good + 1.755146243738946045873491e+4771204 + >>> gammainc(2, 0, 100000001) - gammainc(2, 0, 100000000) # Bad + 0.0 + >>> gammainc(2, 100000000, 100000001) # Good + 4.078258353474186729184421e-43429441 + +The incomplete gamma functions satisfy simple recurrence +relations:: + + >>> mp.dps = 25 + >>> z, a = mpf(3.5), mpf(2) + >>> gammainc(z+1, a); z*gammainc(z,a) + a**z*exp(-a) + 10.60130296933533459267329 + 10.60130296933533459267329 + >>> gammainc(z+1,0,a); z*gammainc(z,0,a) - a**z*exp(-a) + 1.030425427232114336470932 + 1.030425427232114336470932 + +Evaluation at integers and poles:: + + >>> gammainc(-3, -4, -5) + (-0.2214577048967798566234192 + 0.0j) + >>> gammainc(-3, 0, 5) + +inf + +If `z` is an integer, the recurrence reduces the incomplete gamma +function to `P(a) \exp(-a) + Q(b) \exp(-b)` where `P` and +`Q` are polynomials:: + + >>> gammainc(1, 2); exp(-2) + 0.1353352832366126918939995 + 0.1353352832366126918939995 + >>> mp.dps = 50 + >>> identify(gammainc(6, 1, 2), ['exp(-1)', 'exp(-2)']) + '(326*exp(-1) + (-872)*exp(-2))' + +The incomplete gamma functions reduce to functions such as +the exponential integral Ei and the error function for special +arguments:: + + >>> mp.dps = 25 + >>> gammainc(0, 4); -ei(-4) + 0.00377935240984890647887486 + 0.00377935240984890647887486 + >>> gammainc(0.5, 0, 2); sqrt(pi)*erf(sqrt(2)) + 1.691806732945198336509541 + 1.691806732945198336509541 + +""" + +erf = r""" +Computes the error function, `\mathrm{erf}(x)`. The error +function is the normalized antiderivative of the Gaussian function +`\exp(-t^2)`. More precisely, + +.. math:: + + \mathrm{erf}(x) = \frac{2}{\sqrt \pi} \int_0^x \exp(-t^2) \,dt + +**Basic examples** + +Simple values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> erf(0) + 0.0 + >>> erf(1) + 0.842700792949715 + >>> erf(-1) + -0.842700792949715 + >>> erf(inf) + 1.0 + >>> erf(-inf) + -1.0 + +For large real `x`, `\mathrm{erf}(x)` approaches 1 very +rapidly:: + + >>> erf(3) + 0.999977909503001 + >>> erf(5) + 0.999999999998463 + +The error function is an odd function:: + + >>> nprint(chop(taylor(erf, 0, 5))) + [0.0, 1.12838, 0.0, -0.376126, 0.0, 0.112838] + +:func:`~mpmath.erf` implements arbitrary-precision evaluation and +supports complex numbers:: + + >>> mp.dps = 50 + >>> erf(0.5) + 0.52049987781304653768274665389196452873645157575796 + >>> mp.dps = 25 + >>> erf(1+j) + (1.316151281697947644880271 + 0.1904534692378346862841089j) + +Evaluation is supported for large arguments:: + + >>> mp.dps = 25 + >>> erf('1e1000') + 1.0 + >>> erf('-1e1000') + -1.0 + >>> erf('1e-1000') + 1.128379167095512573896159e-1000 + >>> erf('1e7j') + (0.0 + 8.593897639029319267398803e+43429448190317j) + >>> erf('1e7+1e7j') + (0.9999999858172446172631323 + 3.728805278735270407053139e-8j) + +**Related functions** + +See also :func:`~mpmath.erfc`, which is more accurate for large `x`, +and :func:`~mpmath.erfi` which gives the antiderivative of +`\exp(t^2)`. + +The Fresnel integrals :func:`~mpmath.fresnels` and :func:`~mpmath.fresnelc` +are also related to the error function. +""" + +erfc = r""" +Computes the complementary error function, +`\mathrm{erfc}(x) = 1-\mathrm{erf}(x)`. +This function avoids cancellation that occurs when naively +computing the complementary error function as ``1-erf(x)``:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> 1 - erf(10) + 0.0 + >>> erfc(10) + 2.08848758376254e-45 + +:func:`~mpmath.erfc` works accurately even for ludicrously large +arguments:: + + >>> erfc(10**10) + 4.3504398860243e-43429448190325182776 + +Complex arguments are supported:: + + >>> erfc(500+50j) + (1.19739830969552e-107492 + 1.46072418957528e-107491j) + +""" + + +erfi = r""" +Computes the imaginary error function, `\mathrm{erfi}(x)`. +The imaginary error function is defined in analogy with the +error function, but with a positive sign in the integrand: + +.. math :: + + \mathrm{erfi}(x) = \frac{2}{\sqrt \pi} \int_0^x \exp(t^2) \,dt + +Whereas the error function rapidly converges to 1 as `x` grows, +the imaginary error function rapidly diverges to infinity. +The functions are related as +`\mathrm{erfi}(x) = -i\,\mathrm{erf}(ix)` for all complex +numbers `x`. + +**Examples** + +Basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> erfi(0) + 0.0 + >>> erfi(1) + 1.65042575879754 + >>> erfi(-1) + -1.65042575879754 + >>> erfi(inf) + +inf + >>> erfi(-inf) + -inf + +Note the symmetry between erf and erfi:: + + >>> erfi(3j) + (0.0 + 0.999977909503001j) + >>> erf(3) + 0.999977909503001 + >>> erf(1+2j) + (-0.536643565778565 - 5.04914370344703j) + >>> erfi(2+1j) + (-5.04914370344703 - 0.536643565778565j) + +Large arguments are supported:: + + >>> erfi(1000) + 1.71130938718796e+434291 + >>> erfi(10**10) + 7.3167287567024e+43429448190325182754 + >>> erfi(-10**10) + -7.3167287567024e+43429448190325182754 + >>> erfi(1000-500j) + (2.49895233563961e+325717 + 2.6846779342253e+325717j) + >>> erfi(100000j) + (0.0 + 1.0j) + >>> erfi(-100000j) + (0.0 - 1.0j) + + +""" + +erfinv = r""" +Computes the inverse error function, satisfying + +.. math :: + + \mathrm{erf}(\mathrm{erfinv}(x)) = + \mathrm{erfinv}(\mathrm{erf}(x)) = x. + +This function is defined only for `-1 \le x \le 1`. + +**Examples** + +Special values include:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> erfinv(0) + 0.0 + >>> erfinv(1) + +inf + >>> erfinv(-1) + -inf + +The domain is limited to the standard interval:: + + >>> erfinv(2) + Traceback (most recent call last): + ... + ValueError: erfinv(x) is defined only for -1 <= x <= 1 + +It is simple to check that :func:`~mpmath.erfinv` computes inverse values of +:func:`~mpmath.erf` as promised:: + + >>> erf(erfinv(0.75)) + 0.75 + >>> erf(erfinv(-0.995)) + -0.995 + +:func:`~mpmath.erfinv` supports arbitrary-precision evaluation:: + + >>> mp.dps = 50 + >>> x = erf(2) + >>> x + 0.99532226501895273416206925636725292861089179704006 + >>> erfinv(x) + 2.0 + +A definite integral involving the inverse error function:: + + >>> mp.dps = 15 + >>> quad(erfinv, [0, 1]) + 0.564189583547756 + >>> 1/sqrt(pi) + 0.564189583547756 + +The inverse error function can be used to generate random numbers +with a Gaussian distribution (although this is a relatively +inefficient algorithm):: + + >>> nprint([erfinv(2*rand()-1) for n in range(6)]) # doctest: +SKIP + [-0.586747, 1.10233, -0.376796, 0.926037, -0.708142, -0.732012] + +""" + +npdf = r""" +``npdf(x, mu=0, sigma=1)`` evaluates the probability density +function of a normal distribution with mean value `\mu` +and variance `\sigma^2`. + +Elementary properties of the probability distribution can +be verified using numerical integration:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> quad(npdf, [-inf, inf]) + 1.0 + >>> quad(lambda x: npdf(x, 3), [3, inf]) + 0.5 + >>> quad(lambda x: npdf(x, 3, 2), [3, inf]) + 0.5 + +See also :func:`~mpmath.ncdf`, which gives the cumulative +distribution. +""" + +ncdf = r""" +``ncdf(x, mu=0, sigma=1)`` evaluates the cumulative distribution +function of a normal distribution with mean value `\mu` +and variance `\sigma^2`. + +See also :func:`~mpmath.npdf`, which gives the probability density. + +Elementary properties include:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> ncdf(pi, mu=pi) + 0.5 + >>> ncdf(-inf) + 0.0 + >>> ncdf(+inf) + 1.0 + +The cumulative distribution is the integral of the density +function having identical mu and sigma:: + + >>> mp.dps = 15 + >>> diff(ncdf, 2) + 0.053990966513188 + >>> npdf(2) + 0.053990966513188 + >>> diff(lambda x: ncdf(x, 1, 0.5), 0) + 0.107981933026376 + >>> npdf(0, 1, 0.5) + 0.107981933026376 +""" + +expint = r""" +:func:`~mpmath.expint(n,z)` gives the generalized exponential integral +or En-function, + +.. math :: + + \mathrm{E}_n(z) = \int_1^{\infty} \frac{e^{-zt}}{t^n} dt, + +where `n` and `z` may both be complex numbers. The case with `n = 1` is +also given by :func:`~mpmath.e1`. + +**Examples** + +Evaluation at real and complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> expint(1, 6.25) + 0.0002704758872637179088496194 + >>> expint(-3, 2+3j) + (0.00299658467335472929656159 + 0.06100816202125885450319632j) + >>> expint(2+3j, 4-5j) + (0.001803529474663565056945248 - 0.002235061547756185403349091j) + +At negative integer values of `n`, `E_n(z)` reduces to a +rational-exponential function:: + + >>> f = lambda n, z: fac(n)*sum(z**k/fac(k-1) for k in range(1,n+2))/\ + ... exp(z)/z**(n+2) + >>> n = 3 + >>> z = 1/pi + >>> expint(-n,z) + 584.2604820613019908668219 + >>> f(n,z) + 584.2604820613019908668219 + >>> n = 5 + >>> expint(-n,z) + 115366.5762594725451811138 + >>> f(n,z) + 115366.5762594725451811138 +""" + +e1 = r""" +Computes the exponential integral `\mathrm{E}_1(z)`, given by + +.. math :: + + \mathrm{E}_1(z) = \int_z^{\infty} \frac{e^{-t}}{t} dt. + +This is equivalent to :func:`~mpmath.expint` with `n = 1`. + +**Examples** + +Two ways to evaluate this function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> e1(6.25) + 0.0002704758872637179088496194 + >>> expint(1,6.25) + 0.0002704758872637179088496194 + +The E1-function is essentially the same as the Ei-function (:func:`~mpmath.ei`) +with negated argument, except for an imaginary branch cut term:: + + >>> e1(2.5) + 0.02491491787026973549562801 + >>> -ei(-2.5) + 0.02491491787026973549562801 + >>> e1(-2.5) + (-7.073765894578600711923552 - 3.141592653589793238462643j) + >>> -ei(2.5) + -7.073765894578600711923552 + +""" + +ei = r""" +Computes the exponential integral or Ei-function, `\mathrm{Ei}(x)`. +The exponential integral is defined as + +.. math :: + + \mathrm{Ei}(x) = \int_{-\infty\,}^x \frac{e^t}{t} \, dt. + +When the integration range includes `t = 0`, the exponential +integral is interpreted as providing the Cauchy principal value. + +For real `x`, the Ei-function behaves roughly like +`\mathrm{Ei}(x) \approx \exp(x) + \log(|x|)`. + +The Ei-function is related to the more general family of exponential +integral functions denoted by `E_n`, which are available as :func:`~mpmath.expint`. + +**Basic examples** + +Some basic values and limits are:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> ei(0) + -inf + >>> ei(1) + 1.89511781635594 + >>> ei(inf) + +inf + >>> ei(-inf) + 0.0 + +For `x < 0`, the defining integral can be evaluated +numerically as a reference:: + + >>> ei(-4) + -0.00377935240984891 + >>> quad(lambda t: exp(t)/t, [-inf, -4]) + -0.00377935240984891 + +:func:`~mpmath.ei` supports complex arguments and arbitrary +precision evaluation:: + + >>> mp.dps = 50 + >>> ei(pi) + 10.928374389331410348638445906907535171566338835056 + >>> mp.dps = 25 + >>> ei(3+4j) + (-4.154091651642689822535359 + 4.294418620024357476985535j) + +**Related functions** + +The exponential integral is closely related to the logarithmic +integral. See :func:`~mpmath.li` for additional information. + +The exponential integral is related to the hyperbolic +and trigonometric integrals (see :func:`~mpmath.chi`, :func:`~mpmath.shi`, +:func:`~mpmath.ci`, :func:`~mpmath.si`) similarly to how the ordinary +exponential function is related to the hyperbolic and +trigonometric functions:: + + >>> mp.dps = 15 + >>> ei(3) + 9.93383257062542 + >>> chi(3) + shi(3) + 9.93383257062542 + >>> chop(ci(3j) - j*si(3j) - pi*j/2) + 9.93383257062542 + +Beware that logarithmic corrections, as in the last example +above, are required to obtain the correct branch in general. +For details, see [1]. + +The exponential integral is also a special case of the +hypergeometric function `\,_2F_2`:: + + >>> z = 0.6 + >>> z*hyper([1,1],[2,2],z) + (ln(z)-ln(1/z))/2 + euler + 0.769881289937359 + >>> ei(z) + 0.769881289937359 + +**References** + +1. Relations between Ei and other functions: + http://functions.wolfram.com/GammaBetaErf/ExpIntegralEi/27/01/ + +2. Abramowitz & Stegun, section 5: + http://people.math.sfu.ca/~cbm/aands/page_228.htm + +3. Asymptotic expansion for Ei: + http://mathworld.wolfram.com/En-Function.html +""" + +li = r""" +Computes the logarithmic integral or li-function +`\mathrm{li}(x)`, defined by + +.. math :: + + \mathrm{li}(x) = \int_0^x \frac{1}{\log t} \, dt + +The logarithmic integral has a singularity at `x = 1`. + +Alternatively, ``li(x, offset=True)`` computes the offset +logarithmic integral (used in number theory) + +.. math :: + + \mathrm{Li}(x) = \int_2^x \frac{1}{\log t} \, dt. + +These two functions are related via the simple identity +`\mathrm{Li}(x) = \mathrm{li}(x) - \mathrm{li}(2)`. + +The logarithmic integral should also not be confused with +the polylogarithm (also denoted by Li), which is implemented +as :func:`~mpmath.polylog`. + +**Examples** + +Some basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 30; mp.pretty = True + >>> li(0) + 0.0 + >>> li(1) + -inf + >>> li(1) + -inf + >>> li(2) + 1.04516378011749278484458888919 + >>> findroot(li, 2) + 1.45136923488338105028396848589 + >>> li(inf) + +inf + >>> li(2, offset=True) + 0.0 + >>> li(1, offset=True) + -inf + >>> li(0, offset=True) + -1.04516378011749278484458888919 + >>> li(10, offset=True) + 5.12043572466980515267839286347 + +The logarithmic integral can be evaluated for arbitrary +complex arguments:: + + >>> mp.dps = 20 + >>> li(3+4j) + (3.1343755504645775265 + 2.6769247817778742392j) + +The logarithmic integral is related to the exponential integral:: + + >>> ei(log(3)) + 2.1635885946671919729 + >>> li(3) + 2.1635885946671919729 + +The logarithmic integral grows like `O(x/\log(x))`:: + + >>> mp.dps = 15 + >>> x = 10**100 + >>> x/log(x) + 4.34294481903252e+97 + >>> li(x) + 4.3619719871407e+97 + +The prime number theorem states that the number of primes less +than `x` is asymptotic to `\mathrm{Li}(x)` (equivalently +`\mathrm{li}(x)`). For example, it is known that there are +exactly 1,925,320,391,606,803,968,923 prime numbers less than +`10^{23}` [1]. The logarithmic integral provides a very +accurate estimate:: + + >>> li(10**23, offset=True) + 1.92532039161405e+21 + +A definite integral is:: + + >>> quad(li, [0, 1]) + -0.693147180559945 + >>> -ln(2) + -0.693147180559945 + +**References** + +1. http://mathworld.wolfram.com/PrimeCountingFunction.html + +2. http://mathworld.wolfram.com/LogarithmicIntegral.html + +""" + +ci = r""" +Computes the cosine integral, + +.. math :: + + \mathrm{Ci}(x) = -\int_x^{\infty} \frac{\cos t}{t}\,dt + = \gamma + \log x + \int_0^x \frac{\cos t - 1}{t}\,dt + +**Examples** + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> ci(0) + -inf + >>> ci(1) + 0.3374039229009681346626462 + >>> ci(pi) + 0.07366791204642548599010096 + >>> ci(inf) + 0.0 + >>> ci(-inf) + (0.0 + 3.141592653589793238462643j) + >>> ci(2+3j) + (1.408292501520849518759125 - 2.983617742029605093121118j) + +The cosine integral behaves roughly like the sinc function +(see :func:`~mpmath.sinc`) for large real `x`:: + + >>> ci(10**10) + -4.875060251748226537857298e-11 + >>> sinc(10**10) + -4.875060250875106915277943e-11 + >>> chop(limit(ci, inf)) + 0.0 + +It has infinitely many roots on the positive real axis:: + + >>> findroot(ci, 1) + 0.6165054856207162337971104 + >>> findroot(ci, 2) + 3.384180422551186426397851 + +Evaluation is supported for `z` anywhere in the complex plane:: + + >>> ci(10**6*(1+j)) + (4.449410587611035724984376e+434287 + 9.75744874290013526417059e+434287j) + +We can evaluate the defining integral as a reference:: + + >>> mp.dps = 15 + >>> -quadosc(lambda t: cos(t)/t, [5, inf], omega=1) + -0.190029749656644 + >>> ci(5) + -0.190029749656644 + +Some infinite series can be evaluated using the +cosine integral:: + + >>> nsum(lambda k: (-1)**k/(fac(2*k)*(2*k)), [1,inf]) + -0.239811742000565 + >>> ci(1) - euler + -0.239811742000565 + +""" + +si = r""" +Computes the sine integral, + +.. math :: + + \mathrm{Si}(x) = \int_0^x \frac{\sin t}{t}\,dt. + +The sine integral is thus the antiderivative of the sinc +function (see :func:`~mpmath.sinc`). + +**Examples** + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> si(0) + 0.0 + >>> si(1) + 0.9460830703671830149413533 + >>> si(-1) + -0.9460830703671830149413533 + >>> si(pi) + 1.851937051982466170361053 + >>> si(inf) + 1.570796326794896619231322 + >>> si(-inf) + -1.570796326794896619231322 + >>> si(2+3j) + (4.547513889562289219853204 + 1.399196580646054789459839j) + +The sine integral approaches `\pi/2` for large real `x`:: + + >>> si(10**10) + 1.570796326707584656968511 + >>> pi/2 + 1.570796326794896619231322 + +Evaluation is supported for `z` anywhere in the complex plane:: + + >>> si(10**6*(1+j)) + (-9.75744874290013526417059e+434287 + 4.449410587611035724984376e+434287j) + +We can evaluate the defining integral as a reference:: + + >>> mp.dps = 15 + >>> quad(sinc, [0, 5]) + 1.54993124494467 + >>> si(5) + 1.54993124494467 + +Some infinite series can be evaluated using the +sine integral:: + + >>> nsum(lambda k: (-1)**k/(fac(2*k+1)*(2*k+1)), [0,inf]) + 0.946083070367183 + >>> si(1) + 0.946083070367183 + +""" + +chi = r""" +Computes the hyperbolic cosine integral, defined +in analogy with the cosine integral (see :func:`~mpmath.ci`) as + +.. math :: + + \mathrm{Chi}(x) = -\int_x^{\infty} \frac{\cosh t}{t}\,dt + = \gamma + \log x + \int_0^x \frac{\cosh t - 1}{t}\,dt + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> chi(0) + -inf + >>> chi(1) + 0.8378669409802082408946786 + >>> chi(inf) + +inf + >>> findroot(chi, 0.5) + 0.5238225713898644064509583 + >>> chi(2+3j) + (-0.1683628683277204662429321 + 2.625115880451325002151688j) + +Evaluation is supported for `z` anywhere in the complex plane:: + + >>> chi(10**6*(1+j)) + (4.449410587611035724984376e+434287 - 9.75744874290013526417059e+434287j) + +""" + +shi = r""" +Computes the hyperbolic sine integral, defined +in analogy with the sine integral (see :func:`~mpmath.si`) as + +.. math :: + + \mathrm{Shi}(x) = \int_0^x \frac{\sinh t}{t}\,dt. + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> shi(0) + 0.0 + >>> shi(1) + 1.057250875375728514571842 + >>> shi(-1) + -1.057250875375728514571842 + >>> shi(inf) + +inf + >>> shi(2+3j) + (-0.1931890762719198291678095 + 2.645432555362369624818525j) + +Evaluation is supported for `z` anywhere in the complex plane:: + + >>> shi(10**6*(1+j)) + (4.449410587611035724984376e+434287 - 9.75744874290013526417059e+434287j) + +""" + +fresnels = r""" +Computes the Fresnel sine integral + +.. math :: + + S(x) = \int_0^x \sin\left(\frac{\pi t^2}{2}\right) \,dt + +Note that some sources define this function +without the normalization factor `\pi/2`. + +**Examples** + +Some basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> fresnels(0) + 0.0 + >>> fresnels(inf) + 0.5 + >>> fresnels(-inf) + -0.5 + >>> fresnels(1) + 0.4382591473903547660767567 + >>> fresnels(1+2j) + (36.72546488399143842838788 + 15.58775110440458732748279j) + +Comparing with the definition:: + + >>> fresnels(3) + 0.4963129989673750360976123 + >>> quad(lambda t: sin(pi*t**2/2), [0,3]) + 0.4963129989673750360976123 +""" + +fresnelc = r""" +Computes the Fresnel cosine integral + +.. math :: + + C(x) = \int_0^x \cos\left(\frac{\pi t^2}{2}\right) \,dt + +Note that some sources define this function +without the normalization factor `\pi/2`. + +**Examples** + +Some basic values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> fresnelc(0) + 0.0 + >>> fresnelc(inf) + 0.5 + >>> fresnelc(-inf) + -0.5 + >>> fresnelc(1) + 0.7798934003768228294742064 + >>> fresnelc(1+2j) + (16.08787137412548041729489 - 36.22568799288165021578758j) + +Comparing with the definition:: + + >>> fresnelc(3) + 0.6057207892976856295561611 + >>> quad(lambda t: cos(pi*t**2/2), [0,3]) + 0.6057207892976856295561611 +""" + +airyai = r""" +Computes the Airy function `\operatorname{Ai}(z)`, which is +the solution of the Airy differential equation `f''(z) - z f(z) = 0` +with initial conditions + +.. math :: + + \operatorname{Ai}(0) = + \frac{1}{3^{2/3}\Gamma\left(\frac{2}{3}\right)} + + \operatorname{Ai}'(0) = + -\frac{1}{3^{1/3}\Gamma\left(\frac{1}{3}\right)}. + +Other common ways of defining the Ai-function include +integrals such as + +.. math :: + + \operatorname{Ai}(x) = \frac{1}{\pi} + \int_0^{\infty} \cos\left(\frac{1}{3}t^3+xt\right) dt + \qquad x \in \mathbb{R} + + \operatorname{Ai}(z) = \frac{\sqrt{3}}{2\pi} + \int_0^{\infty} + \exp\left(-\frac{t^3}{3}-\frac{z^3}{3t^3}\right) dt. + +The Ai-function is an entire function with a turning point, +behaving roughly like a slowly decaying sine wave for `z < 0` and +like a rapidly decreasing exponential for `z > 0`. +A second solution of the Airy differential equation +is given by `\operatorname{Bi}(z)` (see :func:`~mpmath.airybi`). + +Optionally, with *derivative=alpha*, :func:`airyai` can compute the +`\alpha`-th order fractional derivative with respect to `z`. +For `\alpha = n = 1,2,3,\ldots` this gives the derivative +`\operatorname{Ai}^{(n)}(z)`, and for `\alpha = -n = -1,-2,-3,\ldots` +this gives the `n`-fold iterated integral + +.. math :: + + f_0(z) = \operatorname{Ai}(z) + + f_n(z) = \int_0^z f_{n-1}(t) dt. + +The Ai-function has infinitely many zeros, all located along the +negative half of the real axis. They can be computed with +:func:`~mpmath.airyaizero`. + +**Plots** + +.. literalinclude :: /plots/ai.py +.. image :: /plots/ai.png +.. literalinclude :: /plots/ai_c.py +.. image :: /plots/ai_c.png + +**Basic examples** + +Limits and values include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> airyai(0); 1/(power(3,'2/3')*gamma('2/3')) + 0.3550280538878172392600632 + 0.3550280538878172392600632 + >>> airyai(1) + 0.1352924163128814155241474 + >>> airyai(-1) + 0.5355608832923521187995166 + >>> airyai(inf); airyai(-inf) + 0.0 + 0.0 + +Evaluation is supported for large magnitudes of the argument:: + + >>> airyai(-100) + 0.1767533932395528780908311 + >>> airyai(100) + 2.634482152088184489550553e-291 + >>> airyai(50+50j) + (-5.31790195707456404099817e-68 - 1.163588003770709748720107e-67j) + >>> airyai(-50+50j) + (1.041242537363167632587245e+158 + 3.347525544923600321838281e+157j) + +Huge arguments are also fine:: + + >>> airyai(10**10) + 1.162235978298741779953693e-289529654602171 + >>> airyai(-10**10) + 0.0001736206448152818510510181 + >>> w = airyai(10**10*(1+j)) + >>> w.real + 5.711508683721355528322567e-186339621747698 + >>> w.imag + 1.867245506962312577848166e-186339621747697 + +The first root of the Ai-function is:: + + >>> findroot(airyai, -2) + -2.338107410459767038489197 + >>> airyaizero(1) + -2.338107410459767038489197 + +**Properties and relations** + +Verifying the Airy differential equation:: + + >>> for z in [-3.4, 0, 2.5, 1+2j]: + ... chop(airyai(z,2) - z*airyai(z)) + ... + 0.0 + 0.0 + 0.0 + 0.0 + +The first few terms of the Taylor series expansion around `z = 0` +(every third term is zero):: + + >>> nprint(taylor(airyai, 0, 5)) + [0.355028, -0.258819, 0.0, 0.0591713, -0.0215683, 0.0] + +The Airy functions satisfy the Wronskian relation +`\operatorname{Ai}(z) \operatorname{Bi}'(z) - +\operatorname{Ai}'(z) \operatorname{Bi}(z) = 1/\pi`:: + + >>> z = -0.5 + >>> airyai(z)*airybi(z,1) - airyai(z,1)*airybi(z) + 0.3183098861837906715377675 + >>> 1/pi + 0.3183098861837906715377675 + +The Airy functions can be expressed in terms of Bessel +functions of order `\pm 1/3`. For `\Re[z] \le 0`, we have:: + + >>> z = -3 + >>> airyai(z) + -0.3788142936776580743472439 + >>> y = 2*power(-z,'3/2')/3 + >>> (sqrt(-z) * (besselj('1/3',y) + besselj('-1/3',y)))/3 + -0.3788142936776580743472439 + +**Derivatives and integrals** + +Derivatives of the Ai-function (directly and using :func:`~mpmath.diff`):: + + >>> airyai(-3,1); diff(airyai,-3) + 0.3145837692165988136507873 + 0.3145837692165988136507873 + >>> airyai(-3,2); diff(airyai,-3,2) + 1.136442881032974223041732 + 1.136442881032974223041732 + >>> airyai(1000,1); diff(airyai,1000) + -2.943133917910336090459748e-9156 + -2.943133917910336090459748e-9156 + +Several derivatives at `z = 0`:: + + >>> airyai(0,0); airyai(0,1); airyai(0,2) + 0.3550280538878172392600632 + -0.2588194037928067984051836 + 0.0 + >>> airyai(0,3); airyai(0,4); airyai(0,5) + 0.3550280538878172392600632 + -0.5176388075856135968103671 + 0.0 + >>> airyai(0,15); airyai(0,16); airyai(0,17) + 1292.30211615165475090663 + -3188.655054727379756351861 + 0.0 + +The integral of the Ai-function:: + + >>> airyai(3,-1); quad(airyai, [0,3]) + 0.3299203760070217725002701 + 0.3299203760070217725002701 + >>> airyai(-10,-1); quad(airyai, [0,-10]) + -0.765698403134212917425148 + -0.765698403134212917425148 + +Integrals of high or fractional order:: + + >>> airyai(-2,0.5); differint(airyai,-2,0.5,0) + (0.0 + 0.2453596101351438273844725j) + (0.0 + 0.2453596101351438273844725j) + >>> airyai(-2,-4); differint(airyai,-2,-4,0) + 0.2939176441636809580339365 + 0.2939176441636809580339365 + >>> airyai(0,-1); airyai(0,-2); airyai(0,-3) + 0.0 + 0.0 + 0.0 + +Integrals of the Ai-function can be evaluated at limit points:: + + >>> airyai(-1000000,-1); airyai(-inf,-1) + -0.6666843728311539978751512 + -0.6666666666666666666666667 + >>> airyai(10,-1); airyai(+inf,-1) + 0.3333333332991690159427932 + 0.3333333333333333333333333 + >>> airyai(+inf,-2); airyai(+inf,-3) + +inf + +inf + >>> airyai(-1000000,-2); airyai(-inf,-2) + 666666.4078472650651209742 + +inf + >>> airyai(-1000000,-3); airyai(-inf,-3) + -333333074513.7520264995733 + -inf + +**References** + +1. [DLMF]_ Chapter 9: Airy and Related Functions +2. [WolframFunctions]_ section: Bessel-Type Functions + +""" + +airybi = r""" +Computes the Airy function `\operatorname{Bi}(z)`, which is +the solution of the Airy differential equation `f''(z) - z f(z) = 0` +with initial conditions + +.. math :: + + \operatorname{Bi}(0) = + \frac{1}{3^{1/6}\Gamma\left(\frac{2}{3}\right)} + + \operatorname{Bi}'(0) = + \frac{3^{1/6}}{\Gamma\left(\frac{1}{3}\right)}. + +Like the Ai-function (see :func:`~mpmath.airyai`), the Bi-function +is oscillatory for `z < 0`, but it grows rather than decreases +for `z > 0`. + +Optionally, as for :func:`~mpmath.airyai`, derivatives, integrals +and fractional derivatives can be computed with the *derivative* +parameter. + +The Bi-function has infinitely many zeros along the negative +half-axis, as well as complex zeros, which can all be computed +with :func:`~mpmath.airybizero`. + +**Plots** + +.. literalinclude :: /plots/bi.py +.. image :: /plots/bi.png +.. literalinclude :: /plots/bi_c.py +.. image :: /plots/bi_c.png + +**Basic examples** + +Limits and values include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> airybi(0); 1/(power(3,'1/6')*gamma('2/3')) + 0.6149266274460007351509224 + 0.6149266274460007351509224 + >>> airybi(1) + 1.207423594952871259436379 + >>> airybi(-1) + 0.10399738949694461188869 + >>> airybi(inf); airybi(-inf) + +inf + 0.0 + +Evaluation is supported for large magnitudes of the argument:: + + >>> airybi(-100) + 0.02427388768016013160566747 + >>> airybi(100) + 6.041223996670201399005265e+288 + >>> airybi(50+50j) + (-5.322076267321435669290334e+63 + 1.478450291165243789749427e+65j) + >>> airybi(-50+50j) + (-3.347525544923600321838281e+157 + 1.041242537363167632587245e+158j) + +Huge arguments:: + + >>> airybi(10**10) + 1.369385787943539818688433e+289529654602165 + >>> airybi(-10**10) + 0.001775656141692932747610973 + >>> w = airybi(10**10*(1+j)) + >>> w.real + -6.559955931096196875845858e+186339621747689 + >>> w.imag + -6.822462726981357180929024e+186339621747690 + +The first real root of the Bi-function is:: + + >>> findroot(airybi, -1); airybizero(1) + -1.17371322270912792491998 + -1.17371322270912792491998 + +**Properties and relations** + +Verifying the Airy differential equation:: + + >>> for z in [-3.4, 0, 2.5, 1+2j]: + ... chop(airybi(z,2) - z*airybi(z)) + ... + 0.0 + 0.0 + 0.0 + 0.0 + +The first few terms of the Taylor series expansion around `z = 0` +(every third term is zero):: + + >>> nprint(taylor(airybi, 0, 5)) + [0.614927, 0.448288, 0.0, 0.102488, 0.0373574, 0.0] + +The Airy functions can be expressed in terms of Bessel +functions of order `\pm 1/3`. For `\Re[z] \le 0`, we have:: + + >>> z = -3 + >>> airybi(z) + -0.1982896263749265432206449 + >>> p = 2*power(-z,'3/2')/3 + >>> sqrt(-mpf(z)/3)*(besselj('-1/3',p) - besselj('1/3',p)) + -0.1982896263749265432206449 + +**Derivatives and integrals** + +Derivatives of the Bi-function (directly and using :func:`~mpmath.diff`):: + + >>> airybi(-3,1); diff(airybi,-3) + -0.675611222685258537668032 + -0.675611222685258537668032 + >>> airybi(-3,2); diff(airybi,-3,2) + 0.5948688791247796296619346 + 0.5948688791247796296619346 + >>> airybi(1000,1); diff(airybi,1000) + 1.710055114624614989262335e+9156 + 1.710055114624614989262335e+9156 + +Several derivatives at `z = 0`:: + + >>> airybi(0,0); airybi(0,1); airybi(0,2) + 0.6149266274460007351509224 + 0.4482883573538263579148237 + 0.0 + >>> airybi(0,3); airybi(0,4); airybi(0,5) + 0.6149266274460007351509224 + 0.8965767147076527158296474 + 0.0 + >>> airybi(0,15); airybi(0,16); airybi(0,17) + 2238.332923903442675949357 + 5522.912562599140729510628 + 0.0 + +The integral of the Bi-function:: + + >>> airybi(3,-1); quad(airybi, [0,3]) + 10.06200303130620056316655 + 10.06200303130620056316655 + >>> airybi(-10,-1); quad(airybi, [0,-10]) + -0.01504042480614002045135483 + -0.01504042480614002045135483 + +Integrals of high or fractional order:: + + >>> airybi(-2,0.5); differint(airybi, -2, 0.5, 0) + (0.0 + 0.5019859055341699223453257j) + (0.0 + 0.5019859055341699223453257j) + >>> airybi(-2,-4); differint(airybi,-2,-4,0) + 0.2809314599922447252139092 + 0.2809314599922447252139092 + >>> airybi(0,-1); airybi(0,-2); airybi(0,-3) + 0.0 + 0.0 + 0.0 + +Integrals of the Bi-function can be evaluated at limit points:: + + >>> airybi(-1000000,-1); airybi(-inf,-1) + 0.000002191261128063434047966873 + 0.0 + >>> airybi(10,-1); airybi(+inf,-1) + 147809803.1074067161675853 + +inf + >>> airybi(+inf,-2); airybi(+inf,-3) + +inf + +inf + >>> airybi(-1000000,-2); airybi(-inf,-2) + 0.4482883750599908479851085 + 0.4482883573538263579148237 + >>> gamma('2/3')*power(3,'2/3')/(2*pi) + 0.4482883573538263579148237 + >>> airybi(-100000,-3); airybi(-inf,-3) + -44828.52827206932872493133 + -inf + >>> airybi(-100000,-4); airybi(-inf,-4) + 2241411040.437759489540248 + +inf + +""" + +airyaizero = r""" +Gives the `k`-th zero of the Airy Ai-function, +i.e. the `k`-th number `a_k` ordered by magnitude for which +`\operatorname{Ai}(a_k) = 0`. + +Optionally, with *derivative=1*, the corresponding +zero `a'_k` of the derivative function, i.e. +`\operatorname{Ai}'(a'_k) = 0`, is computed. + +**Examples** + +Some values of `a_k`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> airyaizero(1) + -2.338107410459767038489197 + >>> airyaizero(2) + -4.087949444130970616636989 + >>> airyaizero(3) + -5.520559828095551059129856 + >>> airyaizero(1000) + -281.0315196125215528353364 + +Some values of `a'_k`:: + + >>> airyaizero(1,1) + -1.018792971647471089017325 + >>> airyaizero(2,1) + -3.248197582179836537875424 + >>> airyaizero(3,1) + -4.820099211178735639400616 + >>> airyaizero(1000,1) + -280.9378080358935070607097 + +Verification:: + + >>> chop(airyai(airyaizero(1))) + 0.0 + >>> chop(airyai(airyaizero(1,1),1)) + 0.0 + +""" + +airybizero = r""" +With *complex=False*, gives the `k`-th real zero of the Airy Bi-function, +i.e. the `k`-th number `b_k` ordered by magnitude for which +`\operatorname{Bi}(b_k) = 0`. + +With *complex=True*, gives the `k`-th complex zero in the upper +half plane `\beta_k`. Also the conjugate `\overline{\beta_k}` +is a zero. + +Optionally, with *derivative=1*, the corresponding +zero `b'_k` or `\beta'_k` of the derivative function, i.e. +`\operatorname{Bi}'(b'_k) = 0` or `\operatorname{Bi}'(\beta'_k) = 0`, +is computed. + +**Examples** + +Some values of `b_k`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> airybizero(1) + -1.17371322270912792491998 + >>> airybizero(2) + -3.271093302836352715680228 + >>> airybizero(3) + -4.830737841662015932667709 + >>> airybizero(1000) + -280.9378112034152401578834 + +Some values of `b_k`:: + + >>> airybizero(1,1) + -2.294439682614123246622459 + >>> airybizero(2,1) + -4.073155089071828215552369 + >>> airybizero(3,1) + -5.512395729663599496259593 + >>> airybizero(1000,1) + -281.0315164471118527161362 + +Some values of `\beta_k`:: + + >>> airybizero(1,complex=True) + (0.9775448867316206859469927 + 2.141290706038744575749139j) + >>> airybizero(2,complex=True) + (1.896775013895336346627217 + 3.627291764358919410440499j) + >>> airybizero(3,complex=True) + (2.633157739354946595708019 + 4.855468179979844983174628j) + >>> airybizero(1000,complex=True) + (140.4978560578493018899793 + 243.3907724215792121244867j) + +Some values of `\beta'_k`:: + + >>> airybizero(1,1,complex=True) + (0.2149470745374305676088329 + 1.100600143302797880647194j) + >>> airybizero(2,1,complex=True) + (1.458168309223507392028211 + 2.912249367458445419235083j) + >>> airybizero(3,1,complex=True) + (2.273760763013482299792362 + 4.254528549217097862167015j) + >>> airybizero(1000,1,complex=True) + (140.4509972835270559730423 + 243.3096175398562811896208j) + +Verification:: + + >>> chop(airybi(airybizero(1))) + 0.0 + >>> chop(airybi(airybizero(1,1),1)) + 0.0 + >>> u = airybizero(1,complex=True) + >>> chop(airybi(u)) + 0.0 + >>> chop(airybi(conj(u))) + 0.0 + +The complex zeros (in the upper and lower half-planes respectively) +asymptotically approach the rays `z = R \exp(\pm i \pi /3)`:: + + >>> arg(airybizero(1,complex=True)) + 1.142532510286334022305364 + >>> arg(airybizero(1000,complex=True)) + 1.047271114786212061583917 + >>> arg(airybizero(1000000,complex=True)) + 1.047197624741816183341355 + >>> pi/3 + 1.047197551196597746154214 + +""" + + +ellipk = r""" +Evaluates the complete elliptic integral of the first kind, +`K(m)`, defined by + +.. math :: + + K(m) = \int_0^{\pi/2} \frac{dt}{\sqrt{1-m \sin^2 t}} \, = \, + \frac{\pi}{2} \,_2F_1\left(\frac{1}{2}, \frac{1}{2}, 1, m\right). + +Note that the argument is the parameter `m = k^2`, +not the modulus `k` which is sometimes used. + +**Plots** + +.. literalinclude :: /plots/ellipk.py +.. image :: /plots/ellipk.png + +**Examples** + +Values and limits include:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> ellipk(0) + 1.570796326794896619231322 + >>> ellipk(inf) + (0.0 + 0.0j) + >>> ellipk(-inf) + 0.0 + >>> ellipk(1) + +inf + >>> ellipk(-1) + 1.31102877714605990523242 + >>> ellipk(2) + (1.31102877714605990523242 - 1.31102877714605990523242j) + +Verifying the defining integral and hypergeometric +representation:: + + >>> ellipk(0.5) + 1.85407467730137191843385 + >>> quad(lambda t: (1-0.5*sin(t)**2)**-0.5, [0, pi/2]) + 1.85407467730137191843385 + >>> pi/2*hyp2f1(0.5,0.5,1,0.5) + 1.85407467730137191843385 + +Evaluation is supported for arbitrary complex `m`:: + + >>> ellipk(3+4j) + (0.9111955638049650086562171 + 0.6313342832413452438845091j) + +A definite integral:: + + >>> quad(ellipk, [0, 1]) + 2.0 +""" + +agm = r""" +``agm(a, b)`` computes the arithmetic-geometric mean of `a` and +`b`, defined as the limit of the following iteration: + +.. math :: + + a_0 = a + + b_0 = b + + a_{n+1} = \frac{a_n+b_n}{2} + + b_{n+1} = \sqrt{a_n b_n} + +This function can be called with a single argument, computing +`\mathrm{agm}(a,1) = \mathrm{agm}(1,a)`. + +**Examples** + +It is a well-known theorem that the geometric mean of +two distinct positive numbers is less than the arithmetic +mean. It follows that the arithmetic-geometric mean lies +between the two means:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> a = mpf(3) + >>> b = mpf(4) + >>> sqrt(a*b) + 3.46410161513775 + >>> agm(a,b) + 3.48202767635957 + >>> (a+b)/2 + 3.5 + +The arithmetic-geometric mean is scale-invariant:: + + >>> agm(10*e, 10*pi) + 29.261085515723 + >>> 10*agm(e, pi) + 29.261085515723 + +As an order-of-magnitude estimate, `\mathrm{agm}(1,x) \approx x` +for large `x`:: + + >>> agm(10**10) + 643448704.760133 + >>> agm(10**50) + 1.34814309345871e+48 + +For tiny `x`, `\mathrm{agm}(1,x) \approx -\pi/(2 \log(x/4))`:: + + >>> agm('0.01') + 0.262166887202249 + >>> -pi/2/log('0.0025') + 0.262172347753122 + +The arithmetic-geometric mean can also be computed for complex +numbers:: + + >>> agm(3, 2+j) + (2.51055133276184 + 0.547394054060638j) + +The AGM iteration converges very quickly (each step doubles +the number of correct digits), so :func:`~mpmath.agm` supports efficient +high-precision evaluation:: + + >>> mp.dps = 10000 + >>> a = agm(1,2) + >>> str(a)[-10:] + '1679581912' + +**Mathematical relations** + +The arithmetic-geometric mean may be used to evaluate the +following two parametric definite integrals: + +.. math :: + + I_1 = \int_0^{\infty} + \frac{1}{\sqrt{(x^2+a^2)(x^2+b^2)}} \,dx + + I_2 = \int_0^{\pi/2} + \frac{1}{\sqrt{a^2 \cos^2(x) + b^2 \sin^2(x)}} \,dx + +We have:: + + >>> mp.dps = 15 + >>> a = 3 + >>> b = 4 + >>> f1 = lambda x: ((x**2+a**2)*(x**2+b**2))**-0.5 + >>> f2 = lambda x: ((a*cos(x))**2 + (b*sin(x))**2)**-0.5 + >>> quad(f1, [0, inf]) + 0.451115405388492 + >>> quad(f2, [0, pi/2]) + 0.451115405388492 + >>> pi/(2*agm(a,b)) + 0.451115405388492 + +A formula for `\Gamma(1/4)`:: + + >>> gamma(0.25) + 3.62560990822191 + >>> sqrt(2*sqrt(2*pi**3)/agm(1,sqrt(2))) + 3.62560990822191 + +**Possible issues** + +The branch cut chosen for complex `a` and `b` is somewhat +arbitrary. + +""" + +gegenbauer = r""" +Evaluates the Gegenbauer polynomial, or ultraspherical polynomial, + +.. math :: + + C_n^{(a)}(z) = {n+2a-1 \choose n} \,_2F_1\left(-n, n+2a; + a+\frac{1}{2}; \frac{1}{2}(1-z)\right). + +When `n` is a nonnegative integer, this formula gives a polynomial +in `z` of degree `n`, but all parameters are permitted to be +complex numbers. With `a = 1/2`, the Gegenbauer polynomial +reduces to a Legendre polynomial. + +**Examples** + +Evaluation for arbitrary arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> gegenbauer(3, 0.5, -10) + -2485.0 + >>> gegenbauer(1000, 10, 100) + 3.012757178975667428359374e+2322 + >>> gegenbauer(2+3j, -0.75, -1000j) + (-5038991.358609026523401901 + 9414549.285447104177860806j) + +Evaluation at negative integer orders:: + + >>> gegenbauer(-4, 2, 1.75) + -1.0 + >>> gegenbauer(-4, 3, 1.75) + 0.0 + >>> gegenbauer(-4, 2j, 1.75) + 0.0 + >>> gegenbauer(-7, 0.5, 3) + 8989.0 + +The Gegenbauer polynomials solve the differential equation:: + + >>> n, a = 4.5, 1+2j + >>> f = lambda z: gegenbauer(n, a, z) + >>> for z in [0, 0.75, -0.5j]: + ... chop((1-z**2)*diff(f,z,2) - (2*a+1)*z*diff(f,z) + n*(n+2*a)*f(z)) + ... + 0.0 + 0.0 + 0.0 + +The Gegenbauer polynomials have generating function +`(1-2zt+t^2)^{-a}`:: + + >>> a, z = 2.5, 1 + >>> taylor(lambda t: (1-2*z*t+t**2)**(-a), 0, 3) + [1.0, 5.0, 15.0, 35.0] + >>> [gegenbauer(n,a,z) for n in range(4)] + [1.0, 5.0, 15.0, 35.0] + +The Gegenbauer polynomials are orthogonal on `[-1, 1]` with respect +to the weight `(1-z^2)^{a-\frac{1}{2}}`:: + + >>> a, n, m = 2.5, 4, 5 + >>> Cn = lambda z: gegenbauer(n, a, z, zeroprec=1000) + >>> Cm = lambda z: gegenbauer(m, a, z, zeroprec=1000) + >>> chop(quad(lambda z: Cn(z)*Cm(z)*(1-z**2)*(a-0.5), [-1, 1])) + 0.0 +""" + +laguerre = r""" +Gives the generalized (associated) Laguerre polynomial, defined by + +.. math :: + + L_n^a(z) = \frac{\Gamma(n+b+1)}{\Gamma(b+1) \Gamma(n+1)} + \,_1F_1(-n, a+1, z). + +With `a = 0` and `n` a nonnegative integer, this reduces to an ordinary +Laguerre polynomial, the sequence of which begins +`L_0(z) = 1, L_1(z) = 1-z, L_2(z) = z^2-2z+1, \ldots`. + +The Laguerre polynomials are orthogonal with respect to the weight +`z^a e^{-z}` on `[0, \infty)`. + +**Plots** + +.. literalinclude :: /plots/laguerre.py +.. image :: /plots/laguerre.png + +**Examples** + +Evaluation for arbitrary arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> laguerre(5, 0, 0.25) + 0.03726399739583333333333333 + >>> laguerre(1+j, 0.5, 2+3j) + (4.474921610704496808379097 - 11.02058050372068958069241j) + >>> laguerre(2, 0, 10000) + 49980001.0 + >>> laguerre(2.5, 0, 10000) + -9.327764910194842158583189e+4328 + +The first few Laguerre polynomials, normalized to have integer +coefficients:: + + >>> for n in range(7): + ... chop(taylor(lambda z: fac(n)*laguerre(n, 0, z), 0, n)) + ... + [1.0] + [1.0, -1.0] + [2.0, -4.0, 1.0] + [6.0, -18.0, 9.0, -1.0] + [24.0, -96.0, 72.0, -16.0, 1.0] + [120.0, -600.0, 600.0, -200.0, 25.0, -1.0] + [720.0, -4320.0, 5400.0, -2400.0, 450.0, -36.0, 1.0] + +Verifying orthogonality:: + + >>> Lm = lambda t: laguerre(m,a,t) + >>> Ln = lambda t: laguerre(n,a,t) + >>> a, n, m = 2.5, 2, 3 + >>> chop(quad(lambda t: exp(-t)*t**a*Lm(t)*Ln(t), [0,inf])) + 0.0 + + +""" + +hermite = r""" +Evaluates the Hermite polynomial `H_n(z)`, which may be defined using +the recurrence + +.. math :: + + H_0(z) = 1 + + H_1(z) = 2z + + H_{n+1} = 2z H_n(z) - 2n H_{n-1}(z). + +The Hermite polynomials are orthogonal on `(-\infty, \infty)` with +respect to the weight `e^{-z^2}`. More generally, allowing arbitrary complex +values of `n`, the Hermite function `H_n(z)` is defined as + +.. math :: + + H_n(z) = (2z)^n \,_2F_0\left(-\frac{n}{2}, \frac{1-n}{2}, + -\frac{1}{z^2}\right) + +for `\Re{z} > 0`, or generally + +.. math :: + + H_n(z) = 2^n \sqrt{\pi} \left( + \frac{1}{\Gamma\left(\frac{1-n}{2}\right)} + \,_1F_1\left(-\frac{n}{2}, \frac{1}{2}, z^2\right) - + \frac{2z}{\Gamma\left(-\frac{n}{2}\right)} + \,_1F_1\left(\frac{1-n}{2}, \frac{3}{2}, z^2\right) + \right). + +**Plots** + +.. literalinclude :: /plots/hermite.py +.. image :: /plots/hermite.png + +**Examples** + +Evaluation for arbitrary arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hermite(0, 10) + 1.0 + >>> hermite(1, 10); hermite(2, 10) + 20.0 + 398.0 + >>> hermite(10000, 2) + 4.950440066552087387515653e+19334 + >>> hermite(3, -10**8) + -7999999999999998800000000.0 + >>> hermite(-3, -10**8) + 1.675159751729877682920301e+4342944819032534 + >>> hermite(2+3j, -1+2j) + (-0.07652130602993513389421901 - 0.1084662449961914580276007j) + +Coefficients of the first few Hermite polynomials are:: + + >>> for n in range(7): + ... chop(taylor(lambda z: hermite(n, z), 0, n)) + ... + [1.0] + [0.0, 2.0] + [-2.0, 0.0, 4.0] + [0.0, -12.0, 0.0, 8.0] + [12.0, 0.0, -48.0, 0.0, 16.0] + [0.0, 120.0, 0.0, -160.0, 0.0, 32.0] + [-120.0, 0.0, 720.0, 0.0, -480.0, 0.0, 64.0] + +Values at `z = 0`:: + + >>> for n in range(-5, 9): + ... hermite(n, 0) + ... + 0.02769459142039868792653387 + 0.08333333333333333333333333 + 0.2215567313631895034122709 + 0.5 + 0.8862269254527580136490837 + 1.0 + 0.0 + -2.0 + 0.0 + 12.0 + 0.0 + -120.0 + 0.0 + 1680.0 + +Hermite functions satisfy the differential equation:: + + >>> n = 4 + >>> f = lambda z: hermite(n, z) + >>> z = 1.5 + >>> chop(diff(f,z,2) - 2*z*diff(f,z) + 2*n*f(z)) + 0.0 + +Verifying orthogonality:: + + >>> chop(quad(lambda t: hermite(2,t)*hermite(4,t)*exp(-t**2), [-inf,inf])) + 0.0 + +""" + +jacobi = r""" +``jacobi(n, a, b, x)`` evaluates the Jacobi polynomial +`P_n^{(a,b)}(x)`. The Jacobi polynomials are a special +case of the hypergeometric function `\,_2F_1` given by: + +.. math :: + + P_n^{(a,b)}(x) = {n+a \choose n} + \,_2F_1\left(-n,1+a+b+n,a+1,\frac{1-x}{2}\right). + +Note that this definition generalizes to nonintegral values +of `n`. When `n` is an integer, the hypergeometric series +terminates after a finite number of terms, giving +a polynomial in `x`. + +**Evaluation of Jacobi polynomials** + +A special evaluation is `P_n^{(a,b)}(1) = {n+a \choose n}`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> jacobi(4, 0.5, 0.25, 1) + 2.4609375 + >>> binomial(4+0.5, 4) + 2.4609375 + +A Jacobi polynomial of degree `n` is equal to its +Taylor polynomial of degree `n`. The explicit +coefficients of Jacobi polynomials can therefore +be recovered easily using :func:`~mpmath.taylor`:: + + >>> for n in range(5): + ... nprint(taylor(lambda x: jacobi(n,1,2,x), 0, n)) + ... + [1.0] + [-0.5, 2.5] + [-0.75, -1.5, 5.25] + [0.5, -3.5, -3.5, 10.5] + [0.625, 2.5, -11.25, -7.5, 20.625] + +For nonintegral `n`, the Jacobi "polynomial" is no longer +a polynomial:: + + >>> nprint(taylor(lambda x: jacobi(0.5,1,2,x), 0, 4)) + [0.309983, 1.84119, -1.26933, 1.26699, -1.34808] + +**Orthogonality** + +The Jacobi polynomials are orthogonal on the interval +`[-1, 1]` with respect to the weight function +`w(x) = (1-x)^a (1+x)^b`. That is, +`w(x) P_n^{(a,b)}(x) P_m^{(a,b)}(x)` integrates to +zero if `m \ne n` and to a nonzero number if `m = n`. + +The orthogonality is easy to verify using numerical +quadrature:: + + >>> P = jacobi + >>> f = lambda x: (1-x)**a * (1+x)**b * P(m,a,b,x) * P(n,a,b,x) + >>> a = 2 + >>> b = 3 + >>> m, n = 3, 4 + >>> chop(quad(f, [-1, 1]), 1) + 0.0 + >>> m, n = 4, 4 + >>> quad(f, [-1, 1]) + 1.9047619047619 + +**Differential equation** + +The Jacobi polynomials are solutions of the differential +equation + +.. math :: + + (1-x^2) y'' + (b-a-(a+b+2)x) y' + n (n+a+b+1) y = 0. + +We can verify that :func:`~mpmath.jacobi` approximately satisfies +this equation:: + + >>> from mpmath import * + >>> mp.dps = 15 + >>> a = 2.5 + >>> b = 4 + >>> n = 3 + >>> y = lambda x: jacobi(n,a,b,x) + >>> x = pi + >>> A0 = n*(n+a+b+1)*y(x) + >>> A1 = (b-a-(a+b+2)*x)*diff(y,x) + >>> A2 = (1-x**2)*diff(y,x,2) + >>> nprint(A2 + A1 + A0, 1) + 4.0e-12 + +The difference of order `10^{-12}` is as close to zero as +it could be at 15-digit working precision, since the terms +are large:: + + >>> A0, A1, A2 + (26560.2328981879, -21503.7641037294, -5056.46879445852) + +""" + +legendre = r""" +``legendre(n, x)`` evaluates the Legendre polynomial `P_n(x)`. +The Legendre polynomials are given by the formula + +.. math :: + + P_n(x) = \frac{1}{2^n n!} \frac{d^n}{dx^n} (x^2 -1)^n. + +Alternatively, they can be computed recursively using + +.. math :: + + P_0(x) = 1 + + P_1(x) = x + + (n+1) P_{n+1}(x) = (2n+1) x P_n(x) - n P_{n-1}(x). + +A third definition is in terms of the hypergeometric function +`\,_2F_1`, whereby they can be generalized to arbitrary `n`: + +.. math :: + + P_n(x) = \,_2F_1\left(-n, n+1, 1, \frac{1-x}{2}\right) + +**Plots** + +.. literalinclude :: /plots/legendre.py +.. image :: /plots/legendre.png + +**Basic evaluation** + +The Legendre polynomials assume fixed values at the points +`x = -1` and `x = 1`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> nprint([legendre(n, 1) for n in range(6)]) + [1.0, 1.0, 1.0, 1.0, 1.0, 1.0] + >>> nprint([legendre(n, -1) for n in range(6)]) + [1.0, -1.0, 1.0, -1.0, 1.0, -1.0] + +The coefficients of Legendre polynomials can be recovered +using degree-`n` Taylor expansion:: + + >>> for n in range(5): + ... nprint(chop(taylor(lambda x: legendre(n, x), 0, n))) + ... + [1.0] + [0.0, 1.0] + [-0.5, 0.0, 1.5] + [0.0, -1.5, 0.0, 2.5] + [0.375, 0.0, -3.75, 0.0, 4.375] + +The roots of Legendre polynomials are located symmetrically +on the interval `[-1, 1]`:: + + >>> for n in range(5): + ... nprint(polyroots(taylor(lambda x: legendre(n, x), 0, n)[::-1])) + ... + [] + [0.0] + [-0.57735, 0.57735] + [-0.774597, 0.0, 0.774597] + [-0.861136, -0.339981, 0.339981, 0.861136] + +An example of an evaluation for arbitrary `n`:: + + >>> legendre(0.75, 2+4j) + (1.94952805264875 + 2.1071073099422j) + +**Orthogonality** + +The Legendre polynomials are orthogonal on `[-1, 1]` with respect +to the trivial weight `w(x) = 1`. That is, `P_m(x) P_n(x)` +integrates to zero if `m \ne n` and to `2/(2n+1)` if `m = n`:: + + >>> m, n = 3, 4 + >>> quad(lambda x: legendre(m,x)*legendre(n,x), [-1, 1]) + 0.0 + >>> m, n = 4, 4 + >>> quad(lambda x: legendre(m,x)*legendre(n,x), [-1, 1]) + 0.222222222222222 + +**Differential equation** + +The Legendre polynomials satisfy the differential equation + +.. math :: + + ((1-x^2) y')' + n(n+1) y' = 0. + +We can verify this numerically:: + + >>> n = 3.6 + >>> x = 0.73 + >>> P = legendre + >>> A = diff(lambda t: (1-t**2)*diff(lambda u: P(n,u), t), x) + >>> B = n*(n+1)*P(n,x) + >>> nprint(A+B,1) + 9.0e-16 + +""" + + +legenp = r""" +Calculates the (associated) Legendre function of the first kind of +degree *n* and order *m*, `P_n^m(z)`. Taking `m = 0` gives the ordinary +Legendre function of the first kind, `P_n(z)`. The parameters may be +complex numbers. + +In terms of the Gauss hypergeometric function, the (associated) Legendre +function is defined as + +.. math :: + + P_n^m(z) = \frac{1}{\Gamma(1-m)} \frac{(1+z)^{m/2}}{(1-z)^{m/2}} + \,_2F_1\left(-n, n+1, 1-m, \frac{1-z}{2}\right). + +With *type=3* instead of *type=2*, the alternative +definition + +.. math :: + + \hat{P}_n^m(z) = \frac{1}{\Gamma(1-m)} \frac{(z+1)^{m/2}}{(z-1)^{m/2}} + \,_2F_1\left(-n, n+1, 1-m, \frac{1-z}{2}\right). + +is used. These functions correspond respectively to ``LegendreP[n,m,2,z]`` +and ``LegendreP[n,m,3,z]`` in Mathematica. + +The general solution of the (associated) Legendre differential equation + +.. math :: + + (1-z^2) f''(z) - 2zf'(z) + \left(n(n+1)-\frac{m^2}{1-z^2}\right)f(z) = 0 + +is given by `C_1 P_n^m(z) + C_2 Q_n^m(z)` for arbitrary constants +`C_1`, `C_2`, where `Q_n^m(z)` is a Legendre function of the +second kind as implemented by :func:`~mpmath.legenq`. + +**Examples** + +Evaluation for arbitrary parameters and arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> legenp(2, 0, 10); legendre(2, 10) + 149.5 + 149.5 + >>> legenp(-2, 0.5, 2.5) + (1.972260393822275434196053 - 1.972260393822275434196053j) + >>> legenp(2+3j, 1-j, -0.5+4j) + (-3.335677248386698208736542 - 5.663270217461022307645625j) + >>> chop(legenp(3, 2, -1.5, type=2)) + 28.125 + >>> chop(legenp(3, 2, -1.5, type=3)) + -28.125 + +Verifying the associated Legendre differential equation:: + + >>> n, m = 2, -0.5 + >>> C1, C2 = 1, -3 + >>> f = lambda z: C1*legenp(n,m,z) + C2*legenq(n,m,z) + >>> deq = lambda z: (1-z**2)*diff(f,z,2) - 2*z*diff(f,z) + \ + ... (n*(n+1)-m**2/(1-z**2))*f(z) + >>> for z in [0, 2, -1.5, 0.5+2j]: + ... chop(deq(mpmathify(z))) + ... + 0.0 + 0.0 + 0.0 + 0.0 +""" + +legenq = r""" +Calculates the (associated) Legendre function of the second kind of +degree *n* and order *m*, `Q_n^m(z)`. Taking `m = 0` gives the ordinary +Legendre function of the second kind, `Q_n(z)`. The parameters may be +complex numbers. + +The Legendre functions of the second kind give a second set of +solutions to the (associated) Legendre differential equation. +(See :func:`~mpmath.legenp`.) +Unlike the Legendre functions of the first kind, they are not +polynomials of `z` for integer `n`, `m` but rational or logarithmic +functions with poles at `z = \pm 1`. + +There are various ways to define Legendre functions of +the second kind, giving rise to different complex structure. +A version can be selected using the *type* keyword argument. +The *type=2* and *type=3* functions are given respectively by + +.. math :: + + Q_n^m(z) = \frac{\pi}{2 \sin(\pi m)} + \left( \cos(\pi m) P_n^m(z) - + \frac{\Gamma(1+m+n)}{\Gamma(1-m+n)} P_n^{-m}(z)\right) + + \hat{Q}_n^m(z) = \frac{\pi}{2 \sin(\pi m)} e^{\pi i m} + \left( \hat{P}_n^m(z) - + \frac{\Gamma(1+m+n)}{\Gamma(1-m+n)} \hat{P}_n^{-m}(z)\right) + +where `P` and `\hat{P}` are the *type=2* and *type=3* Legendre functions +of the first kind. The formulas above should be understood as limits +when `m` is an integer. + +These functions correspond to ``LegendreQ[n,m,2,z]`` (or ``LegendreQ[n,m,z]``) +and ``LegendreQ[n,m,3,z]`` in Mathematica. The *type=3* function +is essentially the same as the function defined in +Abramowitz & Stegun (eq. 8.1.3) but with `(z+1)^{m/2}(z-1)^{m/2}` instead +of `(z^2-1)^{m/2}`, giving slightly different branches. + +**Examples** + +Evaluation for arbitrary parameters and arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> legenq(2, 0, 0.5) + -0.8186632680417568557122028 + >>> legenq(-1.5, -2, 2.5) + (0.6655964618250228714288277 + 0.3937692045497259717762649j) + >>> legenq(2-j, 3+4j, -6+5j) + (-10001.95256487468541686564 - 6011.691337610097577791134j) + +Different versions of the function:: + + >>> legenq(2, 1, 0.5) + 0.7298060598018049369381857 + >>> legenq(2, 1, 1.5) + (-7.902916572420817192300921 + 0.1998650072605976600724502j) + >>> legenq(2, 1, 0.5, type=3) + (2.040524284763495081918338 - 0.7298060598018049369381857j) + >>> chop(legenq(2, 1, 1.5, type=3)) + -0.1998650072605976600724502 + +""" + +chebyt = r""" +``chebyt(n, x)`` evaluates the Chebyshev polynomial of the first +kind `T_n(x)`, defined by the identity + +.. math :: + + T_n(\cos x) = \cos(n x). + +The Chebyshev polynomials of the first kind are a special +case of the Jacobi polynomials, and by extension of the +hypergeometric function `\,_2F_1`. They can thus also be +evaluated for nonintegral `n`. + +**Plots** + +.. literalinclude :: /plots/chebyt.py +.. image :: /plots/chebyt.png + +**Basic evaluation** + +The coefficients of the `n`-th polynomial can be recovered +using using degree-`n` Taylor expansion:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(5): + ... nprint(chop(taylor(lambda x: chebyt(n, x), 0, n))) + ... + [1.0] + [0.0, 1.0] + [-1.0, 0.0, 2.0] + [0.0, -3.0, 0.0, 4.0] + [1.0, 0.0, -8.0, 0.0, 8.0] + +**Orthogonality** + +The Chebyshev polynomials of the first kind are orthogonal +on the interval `[-1, 1]` with respect to the weight +function `w(x) = 1/\sqrt{1-x^2}`:: + + >>> f = lambda x: chebyt(m,x)*chebyt(n,x)/sqrt(1-x**2) + >>> m, n = 3, 4 + >>> nprint(quad(f, [-1, 1]),1) + 0.0 + >>> m, n = 4, 4 + >>> quad(f, [-1, 1]) + 1.57079632596448 + +""" + +chebyu = r""" +``chebyu(n, x)`` evaluates the Chebyshev polynomial of the second +kind `U_n(x)`, defined by the identity + +.. math :: + + U_n(\cos x) = \frac{\sin((n+1)x)}{\sin(x)}. + +The Chebyshev polynomials of the second kind are a special +case of the Jacobi polynomials, and by extension of the +hypergeometric function `\,_2F_1`. They can thus also be +evaluated for nonintegral `n`. + +**Plots** + +.. literalinclude :: /plots/chebyu.py +.. image :: /plots/chebyu.png + +**Basic evaluation** + +The coefficients of the `n`-th polynomial can be recovered +using using degree-`n` Taylor expansion:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(5): + ... nprint(chop(taylor(lambda x: chebyu(n, x), 0, n))) + ... + [1.0] + [0.0, 2.0] + [-1.0, 0.0, 4.0] + [0.0, -4.0, 0.0, 8.0] + [1.0, 0.0, -12.0, 0.0, 16.0] + +**Orthogonality** + +The Chebyshev polynomials of the second kind are orthogonal +on the interval `[-1, 1]` with respect to the weight +function `w(x) = \sqrt{1-x^2}`:: + + >>> f = lambda x: chebyu(m,x)*chebyu(n,x)*sqrt(1-x**2) + >>> m, n = 3, 4 + >>> quad(f, [-1, 1]) + 0.0 + >>> m, n = 4, 4 + >>> quad(f, [-1, 1]) + 1.5707963267949 +""" + +besselj = r""" +``besselj(n, x, derivative=0)`` gives the Bessel function of the first kind +`J_n(x)`. Bessel functions of the first kind are defined as +solutions of the differential equation + +.. math :: + + x^2 y'' + x y' + (x^2 - n^2) y = 0 + +which appears, among other things, when solving the radial +part of Laplace's equation in cylindrical coordinates. This +equation has two solutions for given `n`, where the +`J_n`-function is the solution that is nonsingular at `x = 0`. +For positive integer `n`, `J_n(x)` behaves roughly like a sine +(odd `n`) or cosine (even `n`) multiplied by a magnitude factor +that decays slowly as `x \to \pm\infty`. + +Generally, `J_n` is a special case of the hypergeometric +function `\,_0F_1`: + +.. math :: + + J_n(x) = \frac{x^n}{2^n \Gamma(n+1)} + \,_0F_1\left(n+1,-\frac{x^2}{4}\right) + +With *derivative* = `m \ne 0`, the `m`-th derivative + +.. math :: + + \frac{d^m}{dx^m} J_n(x) + +is computed. + +**Plots** + +.. literalinclude :: /plots/besselj.py +.. image :: /plots/besselj.png +.. literalinclude :: /plots/besselj_c.py +.. image :: /plots/besselj_c.png + +**Examples** + +Evaluation is supported for arbitrary arguments, and at +arbitrary precision:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> besselj(2, 1000) + -0.024777229528606 + >>> besselj(4, 0.75) + 0.000801070086542314 + >>> besselj(2, 1000j) + (-2.48071721019185e+432 + 6.41567059811949e-437j) + >>> mp.dps = 25 + >>> besselj(0.75j, 3+4j) + (-2.778118364828153309919653 - 1.5863603889018621585533j) + >>> mp.dps = 50 + >>> besselj(1, pi) + 0.28461534317975275734531059968613140570981118184947 + +Arguments may be large:: + + >>> mp.dps = 25 + >>> besselj(0, 10000) + -0.007096160353388801477265164 + >>> besselj(0, 10**10) + 0.000002175591750246891726859055 + >>> besselj(2, 10**100) + 7.337048736538615712436929e-51 + >>> besselj(2, 10**5*j) + (-3.540725411970948860173735e+43426 + 4.4949812409615803110051e-43433j) + +The Bessel functions of the first kind satisfy simple +symmetries around `x = 0`:: + + >>> mp.dps = 15 + >>> nprint([besselj(n,0) for n in range(5)]) + [1.0, 0.0, 0.0, 0.0, 0.0] + >>> nprint([besselj(n,pi) for n in range(5)]) + [-0.304242, 0.284615, 0.485434, 0.333458, 0.151425] + >>> nprint([besselj(n,-pi) for n in range(5)]) + [-0.304242, -0.284615, 0.485434, -0.333458, 0.151425] + +Roots of Bessel functions are often used:: + + >>> nprint([findroot(j0, k) for k in [2, 5, 8, 11, 14]]) + [2.40483, 5.52008, 8.65373, 11.7915, 14.9309] + >>> nprint([findroot(j1, k) for k in [3, 7, 10, 13, 16]]) + [3.83171, 7.01559, 10.1735, 13.3237, 16.4706] + +The roots are not periodic, but the distance between successive +roots asymptotically approaches `2 \pi`. Bessel functions of +the first kind have the following normalization:: + + >>> quadosc(j0, [0, inf], period=2*pi) + 1.0 + >>> quadosc(j1, [0, inf], period=2*pi) + 1.0 + +For `n = 1/2` or `n = -1/2`, the Bessel function reduces to a +trigonometric function:: + + >>> x = 10 + >>> besselj(0.5, x), sqrt(2/(pi*x))*sin(x) + (-0.13726373575505, -0.13726373575505) + >>> besselj(-0.5, x), sqrt(2/(pi*x))*cos(x) + (-0.211708866331398, -0.211708866331398) + +Derivatives of any order can be computed (negative orders +correspond to integration):: + + >>> mp.dps = 25 + >>> besselj(0, 7.5, 1) + -0.1352484275797055051822405 + >>> diff(lambda x: besselj(0,x), 7.5) + -0.1352484275797055051822405 + >>> besselj(0, 7.5, 10) + -0.1377811164763244890135677 + >>> diff(lambda x: besselj(0,x), 7.5, 10) + -0.1377811164763244890135677 + >>> besselj(0,7.5,-1) - besselj(0,3.5,-1) + -0.1241343240399987693521378 + >>> quad(j0, [3.5, 7.5]) + -0.1241343240399987693521378 + +Differentiation with a noninteger order gives the fractional derivative +in the sense of the Riemann-Liouville differintegral, as computed by +:func:`~mpmath.differint`:: + + >>> mp.dps = 15 + >>> besselj(1, 3.5, 0.75) + -0.385977722939384 + >>> differint(lambda x: besselj(1, x), 3.5, 0.75) + -0.385977722939384 + +""" + +besseli = r""" +``besseli(n, x, derivative=0)`` gives the modified Bessel function of the +first kind, + +.. math :: + + I_n(x) = i^{-n} J_n(ix). + +With *derivative* = `m \ne 0`, the `m`-th derivative + +.. math :: + + \frac{d^m}{dx^m} I_n(x) + +is computed. + +**Plots** + +.. literalinclude :: /plots/besseli.py +.. image :: /plots/besseli.png +.. literalinclude :: /plots/besseli_c.py +.. image :: /plots/besseli_c.png + +**Examples** + +Some values of `I_n(x)`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> besseli(0,0) + 1.0 + >>> besseli(1,0) + 0.0 + >>> besseli(0,1) + 1.266065877752008335598245 + >>> besseli(3.5, 2+3j) + (-0.2904369752642538144289025 - 0.4469098397654815837307006j) + +Arguments may be large:: + + >>> besseli(2, 1000) + 2.480717210191852440616782e+432 + >>> besseli(2, 10**10) + 4.299602851624027900335391e+4342944813 + >>> besseli(2, 6000+10000j) + (-2.114650753239580827144204e+2603 + 4.385040221241629041351886e+2602j) + +For integers `n`, the following integral representation holds:: + + >>> mp.dps = 15 + >>> n = 3 + >>> x = 2.3 + >>> quad(lambda t: exp(x*cos(t))*cos(n*t), [0,pi])/pi + 0.349223221159309 + >>> besseli(n,x) + 0.349223221159309 + +Derivatives and antiderivatives of any order can be computed:: + + >>> mp.dps = 25 + >>> besseli(2, 7.5, 1) + 195.8229038931399062565883 + >>> diff(lambda x: besseli(2,x), 7.5) + 195.8229038931399062565883 + >>> besseli(2, 7.5, 10) + 153.3296508971734525525176 + >>> diff(lambda x: besseli(2,x), 7.5, 10) + 153.3296508971734525525176 + >>> besseli(2,7.5,-1) - besseli(2,3.5,-1) + 202.5043900051930141956876 + >>> quad(lambda x: besseli(2,x), [3.5, 7.5]) + 202.5043900051930141956876 + +""" + +bessely = r""" +``bessely(n, x, derivative=0)`` gives the Bessel function of the second kind, + +.. math :: + + Y_n(x) = \frac{J_n(x) \cos(\pi n) - J_{-n}(x)}{\sin(\pi n)}. + +For `n` an integer, this formula should be understood as a +limit. With *derivative* = `m \ne 0`, the `m`-th derivative + +.. math :: + + \frac{d^m}{dx^m} Y_n(x) + +is computed. + +**Plots** + +.. literalinclude :: /plots/bessely.py +.. image :: /plots/bessely.png +.. literalinclude :: /plots/bessely_c.py +.. image :: /plots/bessely_c.png + +**Examples** + +Some values of `Y_n(x)`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> bessely(0,0), bessely(1,0), bessely(2,0) + (-inf, -inf, -inf) + >>> bessely(1, pi) + 0.3588729167767189594679827 + >>> bessely(0.5, 3+4j) + (9.242861436961450520325216 - 3.085042824915332562522402j) + +Arguments may be large:: + + >>> bessely(0, 10000) + 0.00364780555898660588668872 + >>> bessely(2.5, 10**50) + -4.8952500412050989295774e-26 + >>> bessely(2.5, -10**50) + (0.0 + 4.8952500412050989295774e-26j) + +Derivatives and antiderivatives of any order can be computed:: + + >>> bessely(2, 3.5, 1) + 0.3842618820422660066089231 + >>> diff(lambda x: bessely(2, x), 3.5) + 0.3842618820422660066089231 + >>> bessely(0.5, 3.5, 1) + -0.2066598304156764337900417 + >>> diff(lambda x: bessely(0.5, x), 3.5) + -0.2066598304156764337900417 + >>> diff(lambda x: bessely(2, x), 0.5, 10) + -208173867409.5547350101511 + >>> bessely(2, 0.5, 10) + -208173867409.5547350101511 + >>> bessely(2, 100.5, 100) + 0.02668487547301372334849043 + >>> quad(lambda x: bessely(2,x), [1,3]) + -1.377046859093181969213262 + >>> bessely(2,3,-1) - bessely(2,1,-1) + -1.377046859093181969213262 + +""" + +besselk = r""" +``besselk(n, x)`` gives the modified Bessel function of the +second kind, + +.. math :: + + K_n(x) = \frac{\pi}{2} \frac{I_{-n}(x)-I_{n}(x)}{\sin(\pi n)} + +For `n` an integer, this formula should be understood as a +limit. + +**Plots** + +.. literalinclude :: /plots/besselk.py +.. image :: /plots/besselk.png +.. literalinclude :: /plots/besselk_c.py +.. image :: /plots/besselk_c.png + +**Examples** + +Evaluation is supported for arbitrary complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> besselk(0,1) + 0.4210244382407083333356274 + >>> besselk(0, -1) + (0.4210244382407083333356274 - 3.97746326050642263725661j) + >>> besselk(3.5, 2+3j) + (-0.02090732889633760668464128 + 0.2464022641351420167819697j) + >>> besselk(2+3j, 0.5) + (0.9615816021726349402626083 + 0.1918250181801757416908224j) + +Arguments may be large:: + + >>> besselk(0, 100) + 4.656628229175902018939005e-45 + >>> besselk(1, 10**6) + 4.131967049321725588398296e-434298 + >>> besselk(1, 10**6*j) + (0.001140348428252385844876706 - 0.0005200017201681152909000961j) + >>> besselk(4.5, fmul(10**50, j, exact=True)) + (1.561034538142413947789221e-26 + 1.243554598118700063281496e-25j) + +The point `x = 0` is a singularity (logarithmic if `n = 0`):: + + >>> besselk(0,0) + +inf + >>> besselk(1,0) + +inf + >>> for n in range(-4, 5): + ... print(besselk(n, '1e-1000')) + ... + 4.8e+4001 + 8.0e+3000 + 2.0e+2000 + 1.0e+1000 + 2302.701024509704096466802 + 1.0e+1000 + 2.0e+2000 + 8.0e+3000 + 4.8e+4001 + +""" + +hankel1 = r""" +``hankel1(n,x)`` computes the Hankel function of the first kind, +which is the complex combination of Bessel functions given by + +.. math :: + + H_n^{(1)}(x) = J_n(x) + i Y_n(x). + +**Plots** + +.. literalinclude :: /plots/hankel1.py +.. image :: /plots/hankel1.png +.. literalinclude :: /plots/hankel1_c.py +.. image :: /plots/hankel1_c.png + +**Examples** + +The Hankel function is generally complex-valued:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hankel1(2, pi) + (0.4854339326315091097054957 - 0.0999007139290278787734903j) + >>> hankel1(3.5, pi) + (0.2340002029630507922628888 - 0.6419643823412927142424049j) +""" + +hankel2 = r""" +``hankel2(n,x)`` computes the Hankel function of the second kind, +which is the complex combination of Bessel functions given by + +.. math :: + + H_n^{(2)}(x) = J_n(x) - i Y_n(x). + +**Plots** + +.. literalinclude :: /plots/hankel2.py +.. image :: /plots/hankel2.png +.. literalinclude :: /plots/hankel2_c.py +.. image :: /plots/hankel2_c.png + +**Examples** + +The Hankel function is generally complex-valued:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> hankel2(2, pi) + (0.4854339326315091097054957 + 0.0999007139290278787734903j) + >>> hankel2(3.5, pi) + (0.2340002029630507922628888 + 0.6419643823412927142424049j) +""" + +lambertw = r""" +The Lambert W function `W(z)` is defined as the inverse function +of `w \exp(w)`. In other words, the value of `W(z)` is such that +`z = W(z) \exp(W(z))` for any complex number `z`. + +The Lambert W function is a multivalued function with infinitely +many branches `W_k(z)`, indexed by `k \in \mathbb{Z}`. Each branch +gives a different solution `w` of the equation `z = w \exp(w)`. +All branches are supported by :func:`~mpmath.lambertw`: + +* ``lambertw(z)`` gives the principal solution (branch 0) + +* ``lambertw(z, k)`` gives the solution on branch `k` + +The Lambert W function has two partially real branches: the +principal branch (`k = 0`) is real for real `z > -1/e`, and the +`k = -1` branch is real for `-1/e < z < 0`. All branches except +`k = 0` have a logarithmic singularity at `z = 0`. + +The definition, implementation and choice of branches +is based on [Corless]_. + +**Plots** + +.. literalinclude :: /plots/lambertw.py +.. image :: /plots/lambertw.png +.. literalinclude :: /plots/lambertw_c.py +.. image :: /plots/lambertw_c.png + +**Basic examples** + +The Lambert W function is the inverse of `w \exp(w)`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> w = lambertw(1) + >>> w + 0.5671432904097838729999687 + >>> w*exp(w) + 1.0 + +Any branch gives a valid inverse:: + + >>> w = lambertw(1, k=3) + >>> w + (-2.853581755409037807206819 + 17.11353553941214591260783j) + >>> w = lambertw(1, k=25) + >>> w + (-5.047020464221569709378686 + 155.4763860949415867162066j) + >>> chop(w*exp(w)) + 1.0 + +**Applications to equation-solving** + +The Lambert W function may be used to solve various kinds of +equations, such as finding the value of the infinite power +tower `z^{z^{z^{\ldots}}}`:: + + >>> def tower(z, n): + ... if n == 0: + ... return z + ... return z ** tower(z, n-1) + ... + >>> tower(mpf(0.5), 100) + 0.6411857445049859844862005 + >>> -lambertw(-log(0.5))/log(0.5) + 0.6411857445049859844862005 + +**Properties** + +The Lambert W function grows roughly like the natural logarithm +for large arguments:: + + >>> lambertw(1000); log(1000) + 5.249602852401596227126056 + 6.907755278982137052053974 + >>> lambertw(10**100); log(10**100) + 224.8431064451185015393731 + 230.2585092994045684017991 + +The principal branch of the Lambert W function has a rational +Taylor series expansion around `z = 0`:: + + >>> nprint(taylor(lambertw, 0, 6), 10) + [0.0, 1.0, -1.0, 1.5, -2.666666667, 5.208333333, -10.8] + +Some special values and limits are:: + + >>> lambertw(0) + 0.0 + >>> lambertw(1) + 0.5671432904097838729999687 + >>> lambertw(e) + 1.0 + >>> lambertw(inf) + +inf + >>> lambertw(0, k=-1) + -inf + >>> lambertw(0, k=3) + -inf + >>> lambertw(inf, k=2) + (+inf + 12.56637061435917295385057j) + >>> lambertw(inf, k=3) + (+inf + 18.84955592153875943077586j) + >>> lambertw(-inf, k=3) + (+inf + 21.9911485751285526692385j) + +The `k = 0` and `k = -1` branches join at `z = -1/e` where +`W(z) = -1` for both branches. Since `-1/e` can only be represented +approximately with binary floating-point numbers, evaluating the +Lambert W function at this point only gives `-1` approximately:: + + >>> lambertw(-1/e, 0) + -0.9999999999998371330228251 + >>> lambertw(-1/e, -1) + -1.000000000000162866977175 + +If `-1/e` happens to round in the negative direction, there might be +a small imaginary part:: + + >>> mp.dps = 15 + >>> lambertw(-1/e) + (-1.0 + 8.22007971483662e-9j) + >>> lambertw(-1/e+eps) + -0.999999966242188 + +**References** + +1. [Corless]_ +""" + +barnesg = r""" +Evaluates the Barnes G-function, which generalizes the +superfactorial (:func:`~mpmath.superfac`) and by extension also the +hyperfactorial (:func:`~mpmath.hyperfac`) to the complex numbers +in an analogous way to how the gamma function generalizes +the ordinary factorial. + +The Barnes G-function may be defined in terms of a Weierstrass +product: + +.. math :: + + G(z+1) = (2\pi)^{z/2} e^{-[z(z+1)+\gamma z^2]/2} + \prod_{n=1}^\infty + \left[\left(1+\frac{z}{n}\right)^ne^{-z+z^2/(2n)}\right] + +For positive integers `n`, we have have relation to superfactorials +`G(n) = \mathrm{sf}(n-2) = 0! \cdot 1! \cdots (n-2)!`. + +**Examples** + +Some elementary values and limits of the Barnes G-function:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> barnesg(1), barnesg(2), barnesg(3) + (1.0, 1.0, 1.0) + >>> barnesg(4) + 2.0 + >>> barnesg(5) + 12.0 + >>> barnesg(6) + 288.0 + >>> barnesg(7) + 34560.0 + >>> barnesg(8) + 24883200.0 + >>> barnesg(inf) + +inf + >>> barnesg(0), barnesg(-1), barnesg(-2) + (0.0, 0.0, 0.0) + +Closed-form values are known for some rational arguments:: + + >>> barnesg('1/2') + 0.603244281209446 + >>> sqrt(exp(0.25+log(2)/12)/sqrt(pi)/glaisher**3) + 0.603244281209446 + >>> barnesg('1/4') + 0.29375596533861 + >>> nthroot(exp('3/8')/exp(catalan/pi)/ + ... gamma(0.25)**3/sqrt(glaisher)**9, 4) + 0.29375596533861 + +The Barnes G-function satisfies the functional equation +`G(z+1) = \Gamma(z) G(z)`:: + + >>> z = pi + >>> barnesg(z+1) + 2.39292119327948 + >>> gamma(z)*barnesg(z) + 2.39292119327948 + +The asymptotic growth rate of the Barnes G-function is related to +the Glaisher-Kinkelin constant:: + + >>> limit(lambda n: barnesg(n+1)/(n**(n**2/2-mpf(1)/12)* + ... (2*pi)**(n/2)*exp(-3*n**2/4)), inf) + 0.847536694177301 + >>> exp('1/12')/glaisher + 0.847536694177301 + +The Barnes G-function can be differentiated in closed form:: + + >>> z = 3 + >>> diff(barnesg, z) + 0.264507203401607 + >>> barnesg(z)*((z-1)*psi(0,z)-z+(log(2*pi)+1)/2) + 0.264507203401607 + +Evaluation is supported for arbitrary arguments and at arbitrary +precision:: + + >>> barnesg(6.5) + 2548.7457695685 + >>> barnesg(-pi) + 0.00535976768353037 + >>> barnesg(3+4j) + (-0.000676375932234244 - 4.42236140124728e-5j) + >>> mp.dps = 50 + >>> barnesg(1/sqrt(2)) + 0.81305501090451340843586085064413533788206204124732 + >>> q = barnesg(10j) + >>> q.real + 0.000000000021852360840356557241543036724799812371995850552234 + >>> q.imag + -0.00000000000070035335320062304849020654215545839053210041457588 + >>> mp.dps = 15 + >>> barnesg(100) + 3.10361006263698e+6626 + >>> barnesg(-101) + 0.0 + >>> barnesg(-10.5) + 5.94463017605008e+25 + >>> barnesg(-10000.5) + -6.14322868174828e+167480422 + >>> barnesg(1000j) + (5.21133054865546e-1173597 + 4.27461836811016e-1173597j) + >>> barnesg(-1000+1000j) + (2.43114569750291e+1026623 + 2.24851410674842e+1026623j) + + +**References** + +1. Whittaker & Watson, *A Course of Modern Analysis*, + Cambridge University Press, 4th edition (1927), p.264 +2. http://en.wikipedia.org/wiki/Barnes_G-function +3. http://mathworld.wolfram.com/BarnesG-Function.html + +""" + +superfac = r""" +Computes the superfactorial, defined as the product of +consecutive factorials + +.. math :: + + \mathrm{sf}(n) = \prod_{k=1}^n k! + +For general complex `z`, `\mathrm{sf}(z)` is defined +in terms of the Barnes G-function (see :func:`~mpmath.barnesg`). + +**Examples** + +The first few superfactorials are (OEIS A000178):: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(10): + ... print("%s %s" % (n, superfac(n))) + ... + 0 1.0 + 1 1.0 + 2 2.0 + 3 12.0 + 4 288.0 + 5 34560.0 + 6 24883200.0 + 7 125411328000.0 + 8 5.05658474496e+15 + 9 1.83493347225108e+21 + +Superfactorials grow very rapidly:: + + >>> superfac(1000) + 3.24570818422368e+1177245 + >>> superfac(10**10) + 2.61398543581249e+467427913956904067453 + +Evaluation is supported for arbitrary arguments:: + + >>> mp.dps = 25 + >>> superfac(pi) + 17.20051550121297985285333 + >>> superfac(2+3j) + (-0.005915485633199789627466468 + 0.008156449464604044948738263j) + >>> diff(superfac, 1) + 0.2645072034016070205673056 + +**References** + +1. http://oeis.org/A000178 + +""" + + +hyperfac = r""" +Computes the hyperfactorial, defined for integers as the product + +.. math :: + + H(n) = \prod_{k=1}^n k^k. + + +The hyperfactorial satisfies the recurrence formula `H(z) = z^z H(z-1)`. +It can be defined more generally in terms of the Barnes G-function (see +:func:`~mpmath.barnesg`) and the gamma function by the formula + +.. math :: + + H(z) = \frac{\Gamma(z+1)^z}{G(z)}. + +The extension to complex numbers can also be done via +the integral representation + +.. math :: + + H(z) = (2\pi)^{-z/2} \exp \left[ + {z+1 \choose 2} + \int_0^z \log(t!)\,dt + \right]. + +**Examples** + +The rapidly-growing sequence of hyperfactorials begins +(OEIS A002109):: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(10): + ... print("%s %s" % (n, hyperfac(n))) + ... + 0 1.0 + 1 1.0 + 2 4.0 + 3 108.0 + 4 27648.0 + 5 86400000.0 + 6 4031078400000.0 + 7 3.3197663987712e+18 + 8 5.56964379417266e+25 + 9 2.15779412229419e+34 + +Some even larger hyperfactorials are:: + + >>> hyperfac(1000) + 5.46458120882585e+1392926 + >>> hyperfac(10**10) + 4.60408207642219e+489142638002418704309 + +The hyperfactorial can be evaluated for arbitrary arguments:: + + >>> hyperfac(0.5) + 0.880449235173423 + >>> diff(hyperfac, 1) + 0.581061466795327 + >>> hyperfac(pi) + 205.211134637462 + >>> hyperfac(-10+1j) + (3.01144471378225e+46 - 2.45285242480185e+46j) + +The recurrence property of the hyperfactorial holds +generally:: + + >>> z = 3-4*j + >>> hyperfac(z) + (-4.49795891462086e-7 - 6.33262283196162e-7j) + >>> z**z * hyperfac(z-1) + (-4.49795891462086e-7 - 6.33262283196162e-7j) + >>> z = mpf(-0.6) + >>> chop(z**z * hyperfac(z-1)) + 1.28170142849352 + >>> hyperfac(z) + 1.28170142849352 + +The hyperfactorial may also be computed using the integral +definition:: + + >>> z = 2.5 + >>> hyperfac(z) + 15.9842119922237 + >>> (2*pi)**(-z/2)*exp(binomial(z+1,2) + + ... quad(lambda t: loggamma(t+1), [0, z])) + 15.9842119922237 + +:func:`~mpmath.hyperfac` supports arbitrary-precision evaluation:: + + >>> mp.dps = 50 + >>> hyperfac(10) + 215779412229418562091680268288000000000000000.0 + >>> hyperfac(1/sqrt(2)) + 0.89404818005227001975423476035729076375705084390942 + +**References** + +1. http://oeis.org/A002109 +2. http://mathworld.wolfram.com/Hyperfactorial.html + +""" + +rgamma = r""" +Computes the reciprocal of the gamma function, `1/\Gamma(z)`. This +function evaluates to zero at the poles +of the gamma function, `z = 0, -1, -2, \ldots`. + +**Examples** + +Basic examples:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> rgamma(1) + 1.0 + >>> rgamma(4) + 0.1666666666666666666666667 + >>> rgamma(0); rgamma(-1) + 0.0 + 0.0 + >>> rgamma(1000) + 2.485168143266784862783596e-2565 + >>> rgamma(inf) + 0.0 + +A definite integral that can be evaluated in terms of elementary +integrals:: + + >>> quad(rgamma, [0,inf]) + 2.807770242028519365221501 + >>> e + quad(lambda t: exp(-t)/(pi**2+log(t)**2), [0,inf]) + 2.807770242028519365221501 +""" + +loggamma = r""" +Computes the principal branch of the log-gamma function, +`\ln \Gamma(z)`. Unlike `\ln(\Gamma(z))`, which has infinitely many +complex branch cuts, the principal log-gamma function only has a single +branch cut along the negative half-axis. The principal branch +continuously matches the asymptotic Stirling expansion + +.. math :: + + \ln \Gamma(z) \sim \frac{\ln(2 \pi)}{2} + + \left(z-\frac{1}{2}\right) \ln(z) - z + O(z^{-1}). + +The real parts of both functions agree, but their imaginary +parts generally differ by `2 n \pi` for some `n \in \mathbb{Z}`. +They coincide for `z \in \mathbb{R}, z > 0`. + +Computationally, it is advantageous to use :func:`~mpmath.loggamma` +instead of :func:`~mpmath.gamma` for extremely large arguments. + +**Examples** + +Comparing with `\ln(\Gamma(z))`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> loggamma('13.2'); log(gamma('13.2')) + 20.49400419456603678498394 + 20.49400419456603678498394 + >>> loggamma(3+4j) + (-1.756626784603784110530604 + 4.742664438034657928194889j) + >>> log(gamma(3+4j)) + (-1.756626784603784110530604 - 1.540520869144928548730397j) + >>> log(gamma(3+4j)) + 2*pi*j + (-1.756626784603784110530604 + 4.742664438034657928194889j) + +Note the imaginary parts for negative arguments:: + + >>> loggamma(-0.5); loggamma(-1.5); loggamma(-2.5) + (1.265512123484645396488946 - 3.141592653589793238462643j) + (0.8600470153764810145109327 - 6.283185307179586476925287j) + (-0.05624371649767405067259453 - 9.42477796076937971538793j) + +Some special values:: + + >>> loggamma(1); loggamma(2) + 0.0 + 0.0 + >>> loggamma(3); +ln2 + 0.6931471805599453094172321 + 0.6931471805599453094172321 + >>> loggamma(3.5); log(15*sqrt(pi)/8) + 1.200973602347074224816022 + 1.200973602347074224816022 + >>> loggamma(inf) + +inf + +Huge arguments are permitted:: + + >>> loggamma('1e30') + 6.807755278982137052053974e+31 + >>> loggamma('1e300') + 6.897755278982137052053974e+302 + >>> loggamma('1e3000') + 6.906755278982137052053974e+3003 + >>> loggamma('1e100000000000000000000') + 2.302585092994045684007991e+100000000000000000020 + >>> loggamma('1e30j') + (-1.570796326794896619231322e+30 + 6.807755278982137052053974e+31j) + >>> loggamma('1e300j') + (-1.570796326794896619231322e+300 + 6.897755278982137052053974e+302j) + >>> loggamma('1e3000j') + (-1.570796326794896619231322e+3000 + 6.906755278982137052053974e+3003j) + +The log-gamma function can be integrated analytically +on any interval of unit length:: + + >>> z = 0 + >>> quad(loggamma, [z,z+1]); log(2*pi)/2 + 0.9189385332046727417803297 + 0.9189385332046727417803297 + >>> z = 3+4j + >>> quad(loggamma, [z,z+1]); (log(z)-1)*z + log(2*pi)/2 + (-0.9619286014994750641314421 + 5.219637303741238195688575j) + (-0.9619286014994750641314421 + 5.219637303741238195688575j) + +The derivatives of the log-gamma function are given by the +polygamma function (:func:`~mpmath.psi`):: + + >>> diff(loggamma, -4+3j); psi(0, -4+3j) + (1.688493531222971393607153 + 2.554898911356806978892748j) + (1.688493531222971393607153 + 2.554898911356806978892748j) + >>> diff(loggamma, -4+3j, 2); psi(1, -4+3j) + (-0.1539414829219882371561038 - 0.1020485197430267719746479j) + (-0.1539414829219882371561038 - 0.1020485197430267719746479j) + +The log-gamma function satisfies an additive form of the +recurrence relation for the ordinary gamma function:: + + >>> z = 2+3j + >>> loggamma(z); loggamma(z+1) - log(z) + (-2.092851753092733349564189 + 2.302396543466867626153708j) + (-2.092851753092733349564189 + 2.302396543466867626153708j) + +""" + +siegeltheta = r""" +Computes the Riemann-Siegel theta function, + +.. math :: + + \theta(t) = \frac{ + \log\Gamma\left(\frac{1+2it}{4}\right) - + \log\Gamma\left(\frac{1-2it}{4}\right) + }{2i} - \frac{\log \pi}{2} t. + +The Riemann-Siegel theta function is important in +providing the phase factor for the Z-function +(see :func:`~mpmath.siegelz`). Evaluation is supported for real and +complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> siegeltheta(0) + 0.0 + >>> siegeltheta(inf) + +inf + >>> siegeltheta(-inf) + -inf + >>> siegeltheta(1) + -1.767547952812290388302216 + >>> siegeltheta(10+0.25j) + (-3.068638039426838572528867 + 0.05804937947429712998395177j) + +Arbitrary derivatives may be computed with derivative = k + + >>> siegeltheta(1234, derivative=2) + 0.0004051864079114053109473741 + >>> diff(siegeltheta, 1234, n=2) + 0.0004051864079114053109473741 + + +The Riemann-Siegel theta function has odd symmetry around `t = 0`, +two local extreme points and three real roots including 0 (located +symmetrically):: + + >>> nprint(chop(taylor(siegeltheta, 0, 5))) + [0.0, -2.68609, 0.0, 2.69433, 0.0, -6.40218] + >>> findroot(diffun(siegeltheta), 7) + 6.28983598883690277966509 + >>> findroot(siegeltheta, 20) + 17.84559954041086081682634 + +For large `t`, there is a famous asymptotic formula +for `\theta(t)`, to first order given by:: + + >>> t = mpf(10**6) + >>> siegeltheta(t) + 5488816.353078403444882823 + >>> -t*log(2*pi/t)/2-t/2 + 5488816.745777464310273645 +""" + +grampoint = r""" +Gives the `n`-th Gram point `g_n`, defined as the solution +to the equation `\theta(g_n) = \pi n` where `\theta(t)` +is the Riemann-Siegel theta function (:func:`~mpmath.siegeltheta`). + +The first few Gram points are:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> grampoint(0) + 17.84559954041086081682634 + >>> grampoint(1) + 23.17028270124630927899664 + >>> grampoint(2) + 27.67018221781633796093849 + >>> grampoint(3) + 31.71797995476405317955149 + +Checking the definition:: + + >>> siegeltheta(grampoint(3)) + 9.42477796076937971538793 + >>> 3*pi + 9.42477796076937971538793 + +A large Gram point:: + + >>> grampoint(10**10) + 3293531632.728335454561153 + +Gram points are useful when studying the Z-function +(:func:`~mpmath.siegelz`). See the documentation of that function +for additional examples. + +:func:`~mpmath.grampoint` can solve the defining equation for +nonintegral `n`. There is a fixed point where `g(x) = x`:: + + >>> findroot(lambda x: grampoint(x) - x, 10000) + 9146.698193171459265866198 + +**References** + +1. http://mathworld.wolfram.com/GramPoint.html + +""" + +siegelz = r""" +Computes the Z-function, also known as the Riemann-Siegel Z function, + +.. math :: + + Z(t) = e^{i \theta(t)} \zeta(1/2+it) + +where `\zeta(s)` is the Riemann zeta function (:func:`~mpmath.zeta`) +and where `\theta(t)` denotes the Riemann-Siegel theta function +(see :func:`~mpmath.siegeltheta`). + +Evaluation is supported for real and complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> siegelz(1) + -0.7363054628673177346778998 + >>> siegelz(3+4j) + (-0.1852895764366314976003936 - 0.2773099198055652246992479j) + +The first four derivatives are supported, using the +optional *derivative* keyword argument:: + + >>> siegelz(1234567, derivative=3) + 56.89689348495089294249178 + >>> diff(siegelz, 1234567, n=3) + 56.89689348495089294249178 + + +The Z-function has a Maclaurin expansion:: + + >>> nprint(chop(taylor(siegelz, 0, 4))) + [-1.46035, 0.0, 2.73588, 0.0, -8.39357] + +The Z-function `Z(t)` is equal to `\pm |\zeta(s)|` on the +critical line `s = 1/2+it` (i.e. for real arguments `t` +to `Z`). Its zeros coincide with those of the Riemann zeta +function:: + + >>> findroot(siegelz, 14) + 14.13472514173469379045725 + >>> findroot(siegelz, 20) + 21.02203963877155499262848 + >>> findroot(zeta, 0.5+14j) + (0.5 + 14.13472514173469379045725j) + >>> findroot(zeta, 0.5+20j) + (0.5 + 21.02203963877155499262848j) + +Since the Z-function is real-valued on the critical line +(and unlike `|\zeta(s)|` analytic), it is useful for +investigating the zeros of the Riemann zeta function. +For example, one can use a root-finding algorithm based +on sign changes:: + + >>> findroot(siegelz, [100, 200], solver='bisect') + 176.4414342977104188888926 + +To locate roots, Gram points `g_n` which can be computed +by :func:`~mpmath.grampoint` are useful. If `(-1)^n Z(g_n)` is +positive for two consecutive `n`, then `Z(t)` must have +a zero between those points:: + + >>> g10 = grampoint(10) + >>> g11 = grampoint(11) + >>> (-1)**10 * siegelz(g10) > 0 + True + >>> (-1)**11 * siegelz(g11) > 0 + True + >>> findroot(siegelz, [g10, g11], solver='bisect') + 56.44624769706339480436776 + >>> g10, g11 + (54.67523744685325626632663, 57.54516517954725443703014) + +""" + +riemannr = r""" +Evaluates the Riemann R function, a smooth approximation of the +prime counting function `\pi(x)` (see :func:`~mpmath.primepi`). The Riemann +R function gives a fast numerical approximation useful e.g. to +roughly estimate the number of primes in a given interval. + +The Riemann R function is computed using the rapidly convergent Gram +series, + +.. math :: + + R(x) = 1 + \sum_{k=1}^{\infty} + \frac{\log^k x}{k k! \zeta(k+1)}. + +From the Gram series, one sees that the Riemann R function is a +well-defined analytic function (except for a branch cut along +the negative real half-axis); it can be evaluated for arbitrary +real or complex arguments. + +The Riemann R function gives a very accurate approximation +of the prime counting function. For example, it is wrong by at +most 2 for `x < 1000`, and for `x = 10^9` differs from the exact +value of `\pi(x)` by 79, or less than two parts in a million. +It is about 10 times more accurate than the logarithmic integral +estimate (see :func:`~mpmath.li`), which however is even faster to evaluate. +It is orders of magnitude more accurate than the extremely +fast `x/\log x` estimate. + +**Examples** + +For small arguments, the Riemann R function almost exactly +gives the prime counting function if rounded to the nearest +integer:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> primepi(50), riemannr(50) + (15, 14.9757023241462) + >>> max(abs(primepi(n)-int(round(riemannr(n)))) for n in range(100)) + 1 + >>> max(abs(primepi(n)-int(round(riemannr(n)))) for n in range(300)) + 2 + +The Riemann R function can be evaluated for arguments far too large +for exact determination of `\pi(x)` to be computationally +feasible with any presently known algorithm:: + + >>> riemannr(10**30) + 1.46923988977204e+28 + >>> riemannr(10**100) + 4.3619719871407e+97 + >>> riemannr(10**1000) + 4.3448325764012e+996 + +A comparison of the Riemann R function and logarithmic integral estimates +for `\pi(x)` using exact values of `\pi(10^n)` up to `n = 9`. +The fractional error is shown in parentheses:: + + >>> exact = [4,25,168,1229,9592,78498,664579,5761455,50847534] + >>> for n, p in enumerate(exact): + ... n += 1 + ... r, l = riemannr(10**n), li(10**n) + ... rerr, lerr = nstr((r-p)/p,3), nstr((l-p)/p,3) + ... print("%i %i %s(%s) %s(%s)" % (n, p, r, rerr, l, lerr)) + ... + 1 4 4.56458314100509(0.141) 6.1655995047873(0.541) + 2 25 25.6616332669242(0.0265) 30.1261415840796(0.205) + 3 168 168.359446281167(0.00214) 177.609657990152(0.0572) + 4 1229 1226.93121834343(-0.00168) 1246.13721589939(0.0139) + 5 9592 9587.43173884197(-0.000476) 9629.8090010508(0.00394) + 6 78498 78527.3994291277(0.000375) 78627.5491594622(0.00165) + 7 664579 664667.447564748(0.000133) 664918.405048569(0.000511) + 8 5761455 5761551.86732017(1.68e-5) 5762209.37544803(0.000131) + 9 50847534 50847455.4277214(-1.55e-6) 50849234.9570018(3.35e-5) + +The derivative of the Riemann R function gives the approximate +probability for a number of magnitude `x` to be prime:: + + >>> diff(riemannr, 1000) + 0.141903028110784 + >>> mpf(primepi(1050) - primepi(950)) / 100 + 0.15 + +Evaluation is supported for arbitrary arguments and at arbitrary +precision:: + + >>> mp.dps = 30 + >>> riemannr(7.5) + 3.72934743264966261918857135136 + >>> riemannr(-4+2j) + (-0.551002208155486427591793957644 + 2.16966398138119450043195899746j) + +""" + +primepi = r""" +Evaluates the prime counting function, `\pi(x)`, which gives +the number of primes less than or equal to `x`. The argument +`x` may be fractional. + +The prime counting function is very expensive to evaluate +precisely for large `x`, and the present implementation is +not optimized in any way. For numerical approximation of the +prime counting function, it is better to use :func:`~mpmath.primepi2` +or :func:`~mpmath.riemannr`. + +Some values of the prime counting function:: + + >>> from mpmath import * + >>> [primepi(k) for k in range(20)] + [0, 0, 1, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 8] + >>> primepi(3.5) + 2 + >>> primepi(100000) + 9592 + +""" + +primepi2 = r""" +Returns an interval (as an ``mpi`` instance) providing bounds +for the value of the prime counting function `\pi(x)`. For small +`x`, :func:`~mpmath.primepi2` returns an exact interval based on +the output of :func:`~mpmath.primepi`. For `x > 2656`, a loose interval +based on Schoenfeld's inequality + +.. math :: + + |\pi(x) - \mathrm{li}(x)| < \frac{\sqrt x \log x}{8 \pi} + +is returned. This estimate is rigorous assuming the truth of +the Riemann hypothesis, and can be computed very quickly. + +**Examples** + +Exact values of the prime counting function for small `x`:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> iv.dps = 15; iv.pretty = True + >>> primepi2(10) + [4.0, 4.0] + >>> primepi2(100) + [25.0, 25.0] + >>> primepi2(1000) + [168.0, 168.0] + +Loose intervals are generated for moderately large `x`: + + >>> primepi2(10000), primepi(10000) + ([1209.0, 1283.0], 1229) + >>> primepi2(50000), primepi(50000) + ([5070.0, 5263.0], 5133) + +As `x` increases, the absolute error gets worse while the relative +error improves. The exact value of `\pi(10^{23})` is +1925320391606803968923, and :func:`~mpmath.primepi2` gives 9 significant +digits:: + + >>> p = primepi2(10**23) + >>> p + [1.9253203909477020467e+21, 1.925320392280406229e+21] + >>> mpf(p.delta) / mpf(p.a) + 6.9219865355293e-10 + +A more precise, nonrigorous estimate for `\pi(x)` can be +obtained using the Riemann R function (:func:`~mpmath.riemannr`). +For large enough `x`, the value returned by :func:`~mpmath.primepi2` +essentially amounts to a small perturbation of the value returned by +:func:`~mpmath.riemannr`:: + + >>> primepi2(10**100) + [4.3619719871407024816e+97, 4.3619719871407032404e+97] + >>> riemannr(10**100) + 4.3619719871407e+97 +""" + +primezeta = r""" +Computes the prime zeta function, which is defined +in analogy with the Riemann zeta function (:func:`~mpmath.zeta`) +as + +.. math :: + + P(s) = \sum_p \frac{1}{p^s} + +where the sum is taken over all prime numbers `p`. Although +this sum only converges for `\mathrm{Re}(s) > 1`, the +function is defined by analytic continuation in the +half-plane `\mathrm{Re}(s) > 0`. + +**Examples** + +Arbitrary-precision evaluation for real and complex arguments is +supported:: + + >>> from mpmath import * + >>> mp.dps = 30; mp.pretty = True + >>> primezeta(2) + 0.452247420041065498506543364832 + >>> primezeta(pi) + 0.15483752698840284272036497397 + >>> mp.dps = 50 + >>> primezeta(3) + 0.17476263929944353642311331466570670097541212192615 + >>> mp.dps = 20 + >>> primezeta(3+4j) + (-0.12085382601645763295 - 0.013370403397787023602j) + +The prime zeta function has a logarithmic pole at `s = 1`, +with residue equal to the difference of the Mertens and +Euler constants:: + + >>> primezeta(1) + +inf + >>> extradps(25)(lambda x: primezeta(1+x)+log(x))(+eps) + -0.31571845205389007685 + >>> mertens-euler + -0.31571845205389007685 + +The analytic continuation to `0 < \mathrm{Re}(s) \le 1` +is implemented. In this strip the function exhibits +very complex behavior; on the unit interval, it has poles at +`1/n` for every squarefree integer `n`:: + + >>> primezeta(0.5) # Pole at s = 1/2 + (-inf + 3.1415926535897932385j) + >>> primezeta(0.25) + (-1.0416106801757269036 + 0.52359877559829887308j) + >>> primezeta(0.5+10j) + (0.54892423556409790529 + 0.45626803423487934264j) + +Although evaluation works in principle for any `\mathrm{Re}(s) > 0`, +it should be noted that the evaluation time increases exponentially +as `s` approaches the imaginary axis. + +For large `\mathrm{Re}(s)`, `P(s)` is asymptotic to `2^{-s}`:: + + >>> primezeta(inf) + 0.0 + >>> primezeta(10), mpf(2)**-10 + (0.00099360357443698021786, 0.0009765625) + >>> primezeta(1000) + 9.3326361850321887899e-302 + >>> primezeta(1000+1000j) + (-3.8565440833654995949e-302 - 8.4985390447553234305e-302j) + +**References** + +Carl-Erik Froberg, "On the prime zeta function", +BIT 8 (1968), pp. 187-202. + +""" + +bernpoly = r""" +Evaluates the Bernoulli polynomial `B_n(z)`. + +The first few Bernoulli polynomials are:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(6): + ... nprint(chop(taylor(lambda x: bernpoly(n,x), 0, n))) + ... + [1.0] + [-0.5, 1.0] + [0.166667, -1.0, 1.0] + [0.0, 0.5, -1.5, 1.0] + [-0.0333333, 0.0, 1.0, -2.0, 1.0] + [0.0, -0.166667, 0.0, 1.66667, -2.5, 1.0] + +At `z = 0`, the Bernoulli polynomial evaluates to a +Bernoulli number (see :func:`~mpmath.bernoulli`):: + + >>> bernpoly(12, 0), bernoulli(12) + (-0.253113553113553, -0.253113553113553) + >>> bernpoly(13, 0), bernoulli(13) + (0.0, 0.0) + +Evaluation is accurate for large `n` and small `z`:: + + >>> mp.dps = 25 + >>> bernpoly(100, 0.5) + 2.838224957069370695926416e+78 + >>> bernpoly(1000, 10.5) + 5.318704469415522036482914e+1769 + +""" + +polylog = r""" +Computes the polylogarithm, defined by the sum + +.. math :: + + \mathrm{Li}_s(z) = \sum_{k=1}^{\infty} \frac{z^k}{k^s}. + +This series is convergent only for `|z| < 1`, so elsewhere +the analytic continuation is implied. + +The polylogarithm should not be confused with the logarithmic +integral (also denoted by Li or li), which is implemented +as :func:`~mpmath.li`. + +**Examples** + +The polylogarithm satisfies a huge number of functional identities. +A sample of polylogarithm evaluations is shown below:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> polylog(1,0.5), log(2) + (0.693147180559945, 0.693147180559945) + >>> polylog(2,0.5), (pi**2-6*log(2)**2)/12 + (0.582240526465012, 0.582240526465012) + >>> polylog(2,-phi), -log(phi)**2-pi**2/10 + (-1.21852526068613, -1.21852526068613) + >>> polylog(3,0.5), 7*zeta(3)/8-pi**2*log(2)/12+log(2)**3/6 + (0.53721319360804, 0.53721319360804) + +:func:`~mpmath.polylog` can evaluate the analytic continuation of the +polylogarithm when `s` is an integer:: + + >>> polylog(2, 10) + (0.536301287357863 - 7.23378441241546j) + >>> polylog(2, -10) + -4.1982778868581 + >>> polylog(2, 10j) + (-3.05968879432873 + 3.71678149306807j) + >>> polylog(-2, 10) + -0.150891632373114 + >>> polylog(-2, -10) + 0.067618332081142 + >>> polylog(-2, 10j) + (0.0384353698579347 + 0.0912451798066779j) + +Some more examples, with arguments on the unit circle (note that +the series definition cannot be used for computation here):: + + >>> polylog(2,j) + (-0.205616758356028 + 0.915965594177219j) + >>> j*catalan-pi**2/48 + (-0.205616758356028 + 0.915965594177219j) + >>> polylog(3,exp(2*pi*j/3)) + (-0.534247512515375 + 0.765587078525922j) + >>> -4*zeta(3)/9 + 2*j*pi**3/81 + (-0.534247512515375 + 0.765587078525921j) + +Polylogarithms of different order are related by integration +and differentiation:: + + >>> s, z = 3, 0.5 + >>> polylog(s+1, z) + 0.517479061673899 + >>> quad(lambda t: polylog(s,t)/t, [0, z]) + 0.517479061673899 + >>> z*diff(lambda t: polylog(s+2,t), z) + 0.517479061673899 + +Taylor series expansions around `z = 0` are:: + + >>> for n in range(-3, 4): + ... nprint(taylor(lambda x: polylog(n,x), 0, 5)) + ... + [0.0, 1.0, 8.0, 27.0, 64.0, 125.0] + [0.0, 1.0, 4.0, 9.0, 16.0, 25.0] + [0.0, 1.0, 2.0, 3.0, 4.0, 5.0] + [0.0, 1.0, 1.0, 1.0, 1.0, 1.0] + [0.0, 1.0, 0.5, 0.333333, 0.25, 0.2] + [0.0, 1.0, 0.25, 0.111111, 0.0625, 0.04] + [0.0, 1.0, 0.125, 0.037037, 0.015625, 0.008] + +The series defining the polylogarithm is simultaneously +a Taylor series and an L-series. For certain values of `z`, the +polylogarithm reduces to a pure zeta function:: + + >>> polylog(pi, 1), zeta(pi) + (1.17624173838258, 1.17624173838258) + >>> polylog(pi, -1), -altzeta(pi) + (-0.909670702980385, -0.909670702980385) + +Evaluation for arbitrary, nonintegral `s` is supported +for `z` within the unit circle: + + >>> polylog(3+4j, 0.25) + (0.24258605789446 - 0.00222938275488344j) + >>> nsum(lambda k: 0.25**k / k**(3+4j), [1,inf]) + (0.24258605789446 - 0.00222938275488344j) + +It is also supported outside of the unit circle:: + + >>> polylog(1+j, 20+40j) + (-7.1421172179728 - 3.92726697721369j) + >>> polylog(1+j, 200+400j) + (-5.41934747194626 - 9.94037752563927j) + +**References** + +1. Richard Crandall, "Note on fast polylogarithm computation" + http://www.reed.edu/physics/faculty/crandall/papers/Polylog.pdf +2. http://en.wikipedia.org/wiki/Polylogarithm +3. http://mathworld.wolfram.com/Polylogarithm.html + +""" + +bell = r""" +For `n` a nonnegative integer, ``bell(n,x)`` evaluates the Bell +polynomial `B_n(x)`, the first few of which are + +.. math :: + + B_0(x) = 1 + + B_1(x) = x + + B_2(x) = x^2+x + + B_3(x) = x^3+3x^2+x + +If `x = 1` or :func:`~mpmath.bell` is called with only one argument, it +gives the `n`-th Bell number `B_n`, which is the number of +partitions of a set with `n` elements. By setting the precision to +at least `\log_{10} B_n` digits, :func:`~mpmath.bell` provides fast +calculation of exact Bell numbers. + +In general, :func:`~mpmath.bell` computes + +.. math :: + + B_n(x) = e^{-x} \left(\mathrm{sinc}(\pi n) + E_n(x)\right) + +where `E_n(x)` is the generalized exponential function implemented +by :func:`~mpmath.polyexp`. This is an extension of Dobinski's formula [1], +where the modification is the sinc term ensuring that `B_n(x)` is +continuous in `n`; :func:`~mpmath.bell` can thus be evaluated, +differentiated, etc for arbitrary complex arguments. + +**Examples** + +Simple evaluations:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> bell(0, 2.5) + 1.0 + >>> bell(1, 2.5) + 2.5 + >>> bell(2, 2.5) + 8.75 + +Evaluation for arbitrary complex arguments:: + + >>> bell(5.75+1j, 2-3j) + (-10767.71345136587098445143 - 15449.55065599872579097221j) + +The first few Bell polynomials:: + + >>> for k in range(7): + ... nprint(taylor(lambda x: bell(k,x), 0, k)) + ... + [1.0] + [0.0, 1.0] + [0.0, 1.0, 1.0] + [0.0, 1.0, 3.0, 1.0] + [0.0, 1.0, 7.0, 6.0, 1.0] + [0.0, 1.0, 15.0, 25.0, 10.0, 1.0] + [0.0, 1.0, 31.0, 90.0, 65.0, 15.0, 1.0] + +The first few Bell numbers and complementary Bell numbers:: + + >>> [int(bell(k)) for k in range(10)] + [1, 1, 2, 5, 15, 52, 203, 877, 4140, 21147] + >>> [int(bell(k,-1)) for k in range(10)] + [1, -1, 0, 1, 1, -2, -9, -9, 50, 267] + +Large Bell numbers:: + + >>> mp.dps = 50 + >>> bell(50) + 185724268771078270438257767181908917499221852770.0 + >>> bell(50,-1) + -29113173035759403920216141265491160286912.0 + +Some even larger values:: + + >>> mp.dps = 25 + >>> bell(1000,-1) + -1.237132026969293954162816e+1869 + >>> bell(1000) + 2.989901335682408421480422e+1927 + >>> bell(1000,2) + 6.591553486811969380442171e+1987 + >>> bell(1000,100.5) + 9.101014101401543575679639e+2529 + +A determinant identity satisfied by Bell numbers:: + + >>> mp.dps = 15 + >>> N = 8 + >>> det([[bell(k+j) for j in range(N)] for k in range(N)]) + 125411328000.0 + >>> superfac(N-1) + 125411328000.0 + +**References** + +1. http://mathworld.wolfram.com/DobinskisFormula.html + +""" + +polyexp = r""" +Evaluates the polyexponential function, defined for arbitrary +complex `s`, `z` by the series + +.. math :: + + E_s(z) = \sum_{k=1}^{\infty} \frac{k^s}{k!} z^k. + +`E_s(z)` is constructed from the exponential function analogously +to how the polylogarithm is constructed from the ordinary +logarithm; as a function of `s` (with `z` fixed), `E_s` is an L-series +It is an entire function of both `s` and `z`. + +The polyexponential function provides a generalization of the +Bell polynomials `B_n(x)` (see :func:`~mpmath.bell`) to noninteger orders `n`. +In terms of the Bell polynomials, + +.. math :: + + E_s(z) = e^z B_s(z) - \mathrm{sinc}(\pi s). + +Note that `B_n(x)` and `e^{-x} E_n(x)` are identical if `n` +is a nonzero integer, but not otherwise. In particular, they differ +at `n = 0`. + +**Examples** + +Evaluating a series:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> nsum(lambda k: sqrt(k)/fac(k), [1,inf]) + 2.101755547733791780315904 + >>> polyexp(0.5,1) + 2.101755547733791780315904 + +Evaluation for arbitrary arguments:: + + >>> polyexp(-3-4j, 2.5+2j) + (2.351660261190434618268706 + 1.202966666673054671364215j) + +Evaluation is accurate for tiny function values:: + + >>> polyexp(4, -100) + 3.499471750566824369520223e-36 + +If `n` is a nonpositive integer, `E_n` reduces to a special +instance of the hypergeometric function `\,_pF_q`:: + + >>> n = 3 + >>> x = pi + >>> polyexp(-n,x) + 4.042192318847986561771779 + >>> x*hyper([1]*(n+1), [2]*(n+1), x) + 4.042192318847986561771779 + +""" + +cyclotomic = r""" +Evaluates the cyclotomic polynomial `\Phi_n(x)`, defined by + +.. math :: + + \Phi_n(x) = \prod_{\zeta} (x - \zeta) + +where `\zeta` ranges over all primitive `n`-th roots of unity +(see :func:`~mpmath.unitroots`). An equivalent representation, used +for computation, is + +.. math :: + + \Phi_n(x) = \prod_{d\mid n}(x^d-1)^{\mu(n/d)} = \Phi_n(x) + +where `\mu(m)` denotes the Moebius function. The cyclotomic +polynomials are integer polynomials, the first of which can be +written explicitly as + +.. math :: + + \Phi_0(x) = 1 + + \Phi_1(x) = x - 1 + + \Phi_2(x) = x + 1 + + \Phi_3(x) = x^3 + x^2 + 1 + + \Phi_4(x) = x^2 + 1 + + \Phi_5(x) = x^4 + x^3 + x^2 + x + 1 + + \Phi_6(x) = x^2 - x + 1 + +**Examples** + +The coefficients of low-order cyclotomic polynomials can be recovered +using Taylor expansion:: + + >>> from mpmath import * + >>> mp.dps = 15; mp.pretty = True + >>> for n in range(9): + ... p = chop(taylor(lambda x: cyclotomic(n,x), 0, 10)) + ... print("%s %s" % (n, nstr(p[:10+1-p[::-1].index(1)]))) + ... + 0 [1.0] + 1 [-1.0, 1.0] + 2 [1.0, 1.0] + 3 [1.0, 1.0, 1.0] + 4 [1.0, 0.0, 1.0] + 5 [1.0, 1.0, 1.0, 1.0, 1.0] + 6 [1.0, -1.0, 1.0] + 7 [1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0] + 8 [1.0, 0.0, 0.0, 0.0, 1.0] + +The definition as a product over primitive roots may be checked +by computing the product explicitly (for a real argument, this +method will generally introduce numerical noise in the imaginary +part):: + + >>> mp.dps = 25 + >>> z = 3+4j + >>> cyclotomic(10, z) + (-419.0 - 360.0j) + >>> fprod(z-r for r in unitroots(10, primitive=True)) + (-419.0 - 360.0j) + >>> z = 3 + >>> cyclotomic(10, z) + 61.0 + >>> fprod(z-r for r in unitroots(10, primitive=True)) + (61.0 - 3.146045605088568607055454e-25j) + +Up to permutation, the roots of a given cyclotomic polynomial +can be checked to agree with the list of primitive roots:: + + >>> p = taylor(lambda x: cyclotomic(6,x), 0, 6)[:3] + >>> for r in polyroots(p[::-1]): + ... print(r) + ... + (0.5 - 0.8660254037844386467637232j) + (0.5 + 0.8660254037844386467637232j) + >>> + >>> for r in unitroots(6, primitive=True): + ... print(r) + ... + (0.5 + 0.8660254037844386467637232j) + (0.5 - 0.8660254037844386467637232j) + +""" + +meijerg = r""" +Evaluates the Meijer G-function, defined as + +.. math :: + + G^{m,n}_{p,q} \left( \left. \begin{matrix} + a_1, \dots, a_n ; a_{n+1} \dots a_p \\ + b_1, \dots, b_m ; b_{m+1} \dots b_q + \end{matrix}\; \right| \; z ; r \right) = + \frac{1}{2 \pi i} \int_L + \frac{\prod_{j=1}^m \Gamma(b_j+s) \prod_{j=1}^n\Gamma(1-a_j-s)} + {\prod_{j=n+1}^{p}\Gamma(a_j+s) \prod_{j=m+1}^q \Gamma(1-b_j-s)} + z^{-s/r} ds + +for an appropriate choice of the contour `L` (see references). + +There are `p` elements `a_j`. +The argument *a_s* should be a pair of lists, the first containing the +`n` elements `a_1, \ldots, a_n` and the second containing +the `p-n` elements `a_{n+1}, \ldots a_p`. + +There are `q` elements `b_j`. +The argument *b_s* should be a pair of lists, the first containing the +`m` elements `b_1, \ldots, b_m` and the second containing +the `q-m` elements `b_{m+1}, \ldots b_q`. + +The implicit tuple `(m, n, p, q)` constitutes the order or degree of the +Meijer G-function, and is determined by the lengths of the coefficient +vectors. Confusingly, the indices in this tuple appear in a different order +from the coefficients, but this notation is standard. The many examples +given below should hopefully clear up any potential confusion. + +**Algorithm** + +The Meijer G-function is evaluated as a combination of hypergeometric series. +There are two versions of the function, which can be selected with +the optional *series* argument. + +*series=1* uses a sum of `m` `\,_pF_{q-1}` functions of `z` + +*series=2* uses a sum of `n` `\,_qF_{p-1}` functions of `1/z` + +The default series is chosen based on the degree and `|z|` in order +to be consistent with Mathematica's. This definition of the Meijer G-function +has a discontinuity at `|z| = 1` for some orders, which can +be avoided by explicitly specifying a series. + +Keyword arguments are forwarded to :func:`~mpmath.hypercomb`. + +**Examples** + +Many standard functions are special cases of the Meijer G-function +(possibly rescaled and/or with branch cut corrections). We define +some test parameters:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> a = mpf(0.75) + >>> b = mpf(1.5) + >>> z = mpf(2.25) + +The exponential function: +`e^z = G^{1,0}_{0,1} \left( \left. \begin{matrix} - \\ 0 \end{matrix} \; +\right| \; -z \right)` + + >>> meijerg([[],[]], [[0],[]], -z) + 9.487735836358525720550369 + >>> exp(z) + 9.487735836358525720550369 + +The natural logarithm: +`\log(1+z) = G^{1,2}_{2,2} \left( \left. \begin{matrix} 1, 1 \\ 1, 0 +\end{matrix} \; \right| \; -z \right)` + + >>> meijerg([[1,1],[]], [[1],[0]], z) + 1.178654996341646117219023 + >>> log(1+z) + 1.178654996341646117219023 + +A rational function: +`\frac{z}{z+1} = G^{1,2}_{2,2} \left( \left. \begin{matrix} 1, 1 \\ 1, 1 +\end{matrix} \; \right| \; z \right)` + + >>> meijerg([[1,1],[]], [[1],[1]], z) + 0.6923076923076923076923077 + >>> z/(z+1) + 0.6923076923076923076923077 + +The sine and cosine functions: + +`\frac{1}{\sqrt \pi} \sin(2 \sqrt z) = G^{1,0}_{0,2} \left( \left. \begin{matrix} +- \\ \frac{1}{2}, 0 \end{matrix} \; \right| \; z \right)` + +`\frac{1}{\sqrt \pi} \cos(2 \sqrt z) = G^{1,0}_{0,2} \left( \left. \begin{matrix} +- \\ 0, \frac{1}{2} \end{matrix} \; \right| \; z \right)` + + >>> meijerg([[],[]], [[0.5],[0]], (z/2)**2) + 0.4389807929218676682296453 + >>> sin(z)/sqrt(pi) + 0.4389807929218676682296453 + >>> meijerg([[],[]], [[0],[0.5]], (z/2)**2) + -0.3544090145996275423331762 + >>> cos(z)/sqrt(pi) + -0.3544090145996275423331762 + +Bessel functions: + +`J_a(2 \sqrt z) = G^{1,0}_{0,2} \left( \left. +\begin{matrix} - \\ \frac{a}{2}, -\frac{a}{2} +\end{matrix} \; \right| \; z \right)` + +`Y_a(2 \sqrt z) = G^{2,0}_{1,3} \left( \left. +\begin{matrix} \frac{-a-1}{2} \\ \frac{a}{2}, -\frac{a}{2}, \frac{-a-1}{2} +\end{matrix} \; \right| \; z \right)` + +`(-z)^{a/2} z^{-a/2} I_a(2 \sqrt z) = G^{1,0}_{0,2} \left( \left. +\begin{matrix} - \\ \frac{a}{2}, -\frac{a}{2} +\end{matrix} \; \right| \; -z \right)` + +`2 K_a(2 \sqrt z) = G^{2,0}_{0,2} \left( \left. +\begin{matrix} - \\ \frac{a}{2}, -\frac{a}{2} +\end{matrix} \; \right| \; z \right)` + +As the example with the Bessel *I* function shows, a branch +factor is required for some arguments when inverting the square root. + + >>> meijerg([[],[]], [[a/2],[-a/2]], (z/2)**2) + 0.5059425789597154858527264 + >>> besselj(a,z) + 0.5059425789597154858527264 + >>> meijerg([[],[(-a-1)/2]], [[a/2,-a/2],[(-a-1)/2]], (z/2)**2) + 0.1853868950066556941442559 + >>> bessely(a, z) + 0.1853868950066556941442559 + >>> meijerg([[],[]], [[a/2],[-a/2]], -(z/2)**2) + (0.8685913322427653875717476 + 2.096964974460199200551738j) + >>> (-z)**(a/2) / z**(a/2) * besseli(a, z) + (0.8685913322427653875717476 + 2.096964974460199200551738j) + >>> 0.5*meijerg([[],[]], [[a/2,-a/2],[]], (z/2)**2) + 0.09334163695597828403796071 + >>> besselk(a,z) + 0.09334163695597828403796071 + +Error functions: + +`\sqrt{\pi} z^{2(a-1)} \mathrm{erfc}(z) = G^{2,0}_{1,2} \left( \left. +\begin{matrix} a \\ a-1, a-\frac{1}{2} +\end{matrix} \; \right| \; z, \frac{1}{2} \right)` + + >>> meijerg([[],[a]], [[a-1,a-0.5],[]], z, 0.5) + 0.00172839843123091957468712 + >>> sqrt(pi) * z**(2*a-2) * erfc(z) + 0.00172839843123091957468712 + +A Meijer G-function of higher degree, (1,1,2,3): + + >>> meijerg([[a],[b]], [[a],[b,a-1]], z) + 1.55984467443050210115617 + >>> sin((b-a)*pi)/pi*(exp(z)-1)*z**(a-1) + 1.55984467443050210115617 + +A Meijer G-function of still higher degree, (4,1,2,4), that can +be expanded as a messy combination of exponential integrals: + + >>> meijerg([[a],[2*b-a]], [[b,a,b-0.5,-1-a+2*b],[]], z) + 0.3323667133658557271898061 + >>> chop(4**(a-b+1)*sqrt(pi)*gamma(2*b-2*a)*z**a*\ + ... expint(2*b-2*a, -2*sqrt(-z))*expint(2*b-2*a, 2*sqrt(-z))) + 0.3323667133658557271898061 + +In the following case, different series give different values:: + + >>> chop(meijerg([[1],[0.25]],[[3],[0.5]],-2)) + -0.06417628097442437076207337 + >>> meijerg([[1],[0.25]],[[3],[0.5]],-2,series=1) + 0.1428699426155117511873047 + >>> chop(meijerg([[1],[0.25]],[[3],[0.5]],-2,series=2)) + -0.06417628097442437076207337 + +**References** + +1. http://en.wikipedia.org/wiki/Meijer_G-function + +2. http://mathworld.wolfram.com/MeijerG-Function.html + +3. http://functions.wolfram.com/HypergeometricFunctions/MeijerG/ + +4. http://functions.wolfram.com/HypergeometricFunctions/MeijerG1/ + +""" + +clsin = r""" +Computes the Clausen sine function, defined formally by the series + +.. math :: + + \mathrm{Cl}_s(z) = \sum_{k=1}^{\infty} \frac{\sin(kz)}{k^s}. + +The special case `\mathrm{Cl}_2(z)` (i.e. ``clsin(2,z)``) is the classical +"Clausen function". More generally, the Clausen function is defined for +complex `s` and `z`, even when the series does not converge. The +Clausen function is related to the polylogarithm (:func:`~mpmath.polylog`) as + +.. math :: + + \mathrm{Cl}_s(z) = \frac{1}{2i}\left(\mathrm{Li}_s\left(e^{iz}\right) - + \mathrm{Li}_s\left(e^{-iz}\right)\right) + + = \mathrm{Im}\left[\mathrm{Li}_s(e^{iz})\right] \quad (s, z \in \mathbb{R}), + +and this representation can be taken to provide the analytic continuation of the +series. The complementary function :func:`~mpmath.clcos` gives the corresponding +cosine sum. + +**Examples** + +Evaluation for arbitrarily chosen `s` and `z`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> s, z = 3, 4 + >>> clsin(s, z); nsum(lambda k: sin(z*k)/k**s, [1,inf]) + -0.6533010136329338746275795 + -0.6533010136329338746275795 + +Using `z + \pi` instead of `z` gives an alternating series:: + + >>> clsin(s, z+pi) + 0.8860032351260589402871624 + >>> nsum(lambda k: (-1)**k*sin(z*k)/k**s, [1,inf]) + 0.8860032351260589402871624 + +With `s = 1`, the sum can be expressed in closed form +using elementary functions:: + + >>> z = 1 + sqrt(3) + >>> clsin(1, z) + 0.2047709230104579724675985 + >>> chop((log(1-exp(-j*z)) - log(1-exp(j*z)))/(2*j)) + 0.2047709230104579724675985 + >>> nsum(lambda k: sin(k*z)/k, [1,inf]) + 0.2047709230104579724675985 + +The classical Clausen function `\mathrm{Cl}_2(\theta)` gives the +value of the integral `\int_0^{\theta} -\ln(2\sin(x/2)) dx` for +`0 < \theta < 2 \pi`:: + + >>> cl2 = lambda t: clsin(2, t) + >>> cl2(3.5) + -0.2465045302347694216534255 + >>> -quad(lambda x: ln(2*sin(0.5*x)), [0, 3.5]) + -0.2465045302347694216534255 + +This function is symmetric about `\theta = \pi` with zeros and extreme +points:: + + >>> cl2(0); cl2(pi/3); chop(cl2(pi)); cl2(5*pi/3); chop(cl2(2*pi)) + 0.0 + 1.014941606409653625021203 + 0.0 + -1.014941606409653625021203 + 0.0 + +Catalan's constant is a special value:: + + >>> cl2(pi/2) + 0.9159655941772190150546035 + >>> +catalan + 0.9159655941772190150546035 + +The Clausen sine function can be expressed in closed form when +`s` is an odd integer (becoming zero when `s` < 0):: + + >>> z = 1 + sqrt(2) + >>> clsin(1, z); (pi-z)/2 + 0.3636895456083490948304773 + 0.3636895456083490948304773 + >>> clsin(3, z); pi**2/6*z - pi*z**2/4 + z**3/12 + 0.5661751584451144991707161 + 0.5661751584451144991707161 + >>> clsin(-1, z) + 0.0 + >>> clsin(-3, z) + 0.0 + +It can also be expressed in closed form for even integer `s \le 0`, +providing a finite sum for series such as +`\sin(z) + \sin(2z) + \sin(3z) + \ldots`:: + + >>> z = 1 + sqrt(2) + >>> clsin(0, z) + 0.1903105029507513881275865 + >>> cot(z/2)/2 + 0.1903105029507513881275865 + >>> clsin(-2, z) + -0.1089406163841548817581392 + >>> -cot(z/2)*csc(z/2)**2/4 + -0.1089406163841548817581392 + +Call with ``pi=True`` to multiply `z` by `\pi` exactly:: + + >>> clsin(3, 3*pi) + -8.892316224968072424732898e-26 + >>> clsin(3, 3, pi=True) + 0.0 + +Evaluation for complex `s`, `z` in a nonconvergent case:: + + >>> s, z = -1-j, 1+2j + >>> clsin(s, z) + (-0.593079480117379002516034 + 0.9038644233367868273362446j) + >>> extraprec(20)(nsum)(lambda k: sin(k*z)/k**s, [1,inf]) + (-0.593079480117379002516034 + 0.9038644233367868273362446j) + +""" + +clcos = r""" +Computes the Clausen cosine function, defined formally by the series + +.. math :: + + \mathrm{\widetilde{Cl}}_s(z) = \sum_{k=1}^{\infty} \frac{\cos(kz)}{k^s}. + +This function is complementary to the Clausen sine function +:func:`~mpmath.clsin`. In terms of the polylogarithm, + +.. math :: + + \mathrm{\widetilde{Cl}}_s(z) = + \frac{1}{2}\left(\mathrm{Li}_s\left(e^{iz}\right) + + \mathrm{Li}_s\left(e^{-iz}\right)\right) + + = \mathrm{Re}\left[\mathrm{Li}_s(e^{iz})\right] \quad (s, z \in \mathbb{R}). + +**Examples** + +Evaluation for arbitrarily chosen `s` and `z`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> s, z = 3, 4 + >>> clcos(s, z); nsum(lambda k: cos(z*k)/k**s, [1,inf]) + -0.6518926267198991308332759 + -0.6518926267198991308332759 + +Using `z + \pi` instead of `z` gives an alternating series:: + + >>> s, z = 3, 0.5 + >>> clcos(s, z+pi) + -0.8155530586502260817855618 + >>> nsum(lambda k: (-1)**k*cos(z*k)/k**s, [1,inf]) + -0.8155530586502260817855618 + +With `s = 1`, the sum can be expressed in closed form +using elementary functions:: + + >>> z = 1 + sqrt(3) + >>> clcos(1, z) + -0.6720334373369714849797918 + >>> chop(-0.5*(log(1-exp(j*z))+log(1-exp(-j*z)))) + -0.6720334373369714849797918 + >>> -log(abs(2*sin(0.5*z))) # Equivalent to above when z is real + -0.6720334373369714849797918 + >>> nsum(lambda k: cos(k*z)/k, [1,inf]) + -0.6720334373369714849797918 + +It can also be expressed in closed form when `s` is an even integer. +For example, + + >>> clcos(2,z) + -0.7805359025135583118863007 + >>> pi**2/6 - pi*z/2 + z**2/4 + -0.7805359025135583118863007 + +The case `s = 0` gives the renormalized sum of +`\cos(z) + \cos(2z) + \cos(3z) + \ldots` (which happens to be the same for +any value of `z`):: + + >>> clcos(0, z) + -0.5 + >>> nsum(lambda k: cos(k*z), [1,inf]) + -0.5 + +Also the sums + +.. math :: + + \cos(z) + 2\cos(2z) + 3\cos(3z) + \ldots + +and + +.. math :: + + \cos(z) + 2^n \cos(2z) + 3^n \cos(3z) + \ldots + +for higher integer powers `n = -s` can be done in closed form. They are zero +when `n` is positive and even (`s` negative and even):: + + >>> clcos(-1, z); 1/(2*cos(z)-2) + -0.2607829375240542480694126 + -0.2607829375240542480694126 + >>> clcos(-3, z); (2+cos(z))*csc(z/2)**4/8 + 0.1472635054979944390848006 + 0.1472635054979944390848006 + >>> clcos(-2, z); clcos(-4, z); clcos(-6, z) + 0.0 + 0.0 + 0.0 + +With `z = \pi`, the series reduces to that of the Riemann zeta function +(more generally, if `z = p \pi/q`, it is a finite sum over Hurwitz zeta +function values):: + + >>> clcos(2.5, 0); zeta(2.5) + 1.34148725725091717975677 + 1.34148725725091717975677 + >>> clcos(2.5, pi); -altzeta(2.5) + -0.8671998890121841381913472 + -0.8671998890121841381913472 + +Call with ``pi=True`` to multiply `z` by `\pi` exactly:: + + >>> clcos(-3, 2*pi) + 2.997921055881167659267063e+102 + >>> clcos(-3, 2, pi=True) + 0.008333333333333333333333333 + +Evaluation for complex `s`, `z` in a nonconvergent case:: + + >>> s, z = -1-j, 1+2j + >>> clcos(s, z) + (0.9407430121562251476136807 + 0.715826296033590204557054j) + >>> extraprec(20)(nsum)(lambda k: cos(k*z)/k**s, [1,inf]) + (0.9407430121562251476136807 + 0.715826296033590204557054j) + +""" + +whitm = r""" +Evaluates the Whittaker function `M(k,m,z)`, which gives a solution +to the Whittaker differential equation + +.. math :: + + \frac{d^2f}{dz^2} + \left(-\frac{1}{4}+\frac{k}{z}+ + \frac{(\frac{1}{4}-m^2)}{z^2}\right) f = 0. + +A second solution is given by :func:`~mpmath.whitw`. + +The Whittaker functions are defined in Abramowitz & Stegun, section 13.1. +They are alternate forms of the confluent hypergeometric functions +`\,_1F_1` and `U`: + +.. math :: + + M(k,m,z) = e^{-\frac{1}{2}z} z^{\frac{1}{2}+m} + \,_1F_1(\tfrac{1}{2}+m-k, 1+2m, z) + + W(k,m,z) = e^{-\frac{1}{2}z} z^{\frac{1}{2}+m} + U(\tfrac{1}{2}+m-k, 1+2m, z). + +**Examples** + +Evaluation for arbitrary real and complex arguments is supported:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> whitm(1, 1, 1) + 0.7302596799460411820509668 + >>> whitm(1, 1, -1) + (0.0 - 1.417977827655098025684246j) + >>> whitm(j, j/2, 2+3j) + (3.245477713363581112736478 - 0.822879187542699127327782j) + >>> whitm(2, 3, 100000) + 4.303985255686378497193063e+21707 + +Evaluation at zero:: + + >>> whitm(1,-1,0); whitm(1,-0.5,0); whitm(1,0,0) + +inf + nan + 0.0 + +We can verify that :func:`~mpmath.whitm` numerically satisfies the +differential equation for arbitrarily chosen values:: + + >>> k = mpf(0.25) + >>> m = mpf(1.5) + >>> f = lambda z: whitm(k,m,z) + >>> for z in [-1, 2.5, 3, 1+2j]: + ... chop(diff(f,z,2) + (-0.25 + k/z + (0.25-m**2)/z**2)*f(z)) + ... + 0.0 + 0.0 + 0.0 + 0.0 + +An integral involving both :func:`~mpmath.whitm` and :func:`~mpmath.whitw`, +verifying evaluation along the real axis:: + + >>> quad(lambda x: exp(-x)*whitm(3,2,x)*whitw(1,-2,x), [0,inf]) + 3.438869842576800225207341 + >>> 128/(21*sqrt(pi)) + 3.438869842576800225207341 + +""" + +whitw = r""" +Evaluates the Whittaker function `W(k,m,z)`, which gives a second +solution to the Whittaker differential equation. (See :func:`~mpmath.whitm`.) + +**Examples** + +Evaluation for arbitrary real and complex arguments is supported:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> whitw(1, 1, 1) + 1.19532063107581155661012 + >>> whitw(1, 1, -1) + (-0.9424875979222187313924639 - 0.2607738054097702293308689j) + >>> whitw(j, j/2, 2+3j) + (0.1782899315111033879430369 - 0.01609578360403649340169406j) + >>> whitw(2, 3, 100000) + 1.887705114889527446891274e-21705 + >>> whitw(-1, -1, 100) + 1.905250692824046162462058e-24 + +Evaluation at zero:: + + >>> for m in [-1, -0.5, 0, 0.5, 1]: + ... whitw(1, m, 0) + ... + +inf + nan + 0.0 + nan + +inf + +We can verify that :func:`~mpmath.whitw` numerically satisfies the +differential equation for arbitrarily chosen values:: + + >>> k = mpf(0.25) + >>> m = mpf(1.5) + >>> f = lambda z: whitw(k,m,z) + >>> for z in [-1, 2.5, 3, 1+2j]: + ... chop(diff(f,z,2) + (-0.25 + k/z + (0.25-m**2)/z**2)*f(z)) + ... + 0.0 + 0.0 + 0.0 + 0.0 + +""" + +ber = r""" +Computes the Kelvin function ber, which for real arguments gives the real part +of the Bessel J function of a rotated argument + +.. math :: + + J_n\left(x e^{3\pi i/4}\right) = \mathrm{ber}_n(x) + i \mathrm{bei}_n(x). + +The imaginary part is given by :func:`~mpmath.bei`. + +**Plots** + +.. literalinclude :: /plots/ber.py +.. image :: /plots/ber.png + +**Examples** + +Verifying the defining relation:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> n, x = 2, 3.5 + >>> ber(n,x) + 1.442338852571888752631129 + >>> bei(n,x) + -0.948359035324558320217678 + >>> besselj(n, x*root(1,8,3)) + (1.442338852571888752631129 - 0.948359035324558320217678j) + +The ber and bei functions are also defined by analytic continuation +for complex arguments:: + + >>> ber(1+j, 2+3j) + (4.675445984756614424069563 - 15.84901771719130765656316j) + >>> bei(1+j, 2+3j) + (15.83886679193707699364398 + 4.684053288183046528703611j) + +""" + +bei = r""" +Computes the Kelvin function bei, which for real arguments gives the +imaginary part of the Bessel J function of a rotated argument. +See :func:`~mpmath.ber`. +""" + +ker = r""" +Computes the Kelvin function ker, which for real arguments gives the real part +of the (rescaled) Bessel K function of a rotated argument + +.. math :: + + e^{-\pi i/2} K_n\left(x e^{3\pi i/4}\right) = \mathrm{ker}_n(x) + i \mathrm{kei}_n(x). + +The imaginary part is given by :func:`~mpmath.kei`. + +**Plots** + +.. literalinclude :: /plots/ker.py +.. image :: /plots/ker.png + +**Examples** + +Verifying the defining relation:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> n, x = 2, 4.5 + >>> ker(n,x) + 0.02542895201906369640249801 + >>> kei(n,x) + -0.02074960467222823237055351 + >>> exp(-n*pi*j/2) * besselk(n, x*root(1,8,1)) + (0.02542895201906369640249801 - 0.02074960467222823237055351j) + +The ker and kei functions are also defined by analytic continuation +for complex arguments:: + + >>> ker(1+j, 3+4j) + (1.586084268115490421090533 - 2.939717517906339193598719j) + >>> kei(1+j, 3+4j) + (-2.940403256319453402690132 - 1.585621643835618941044855j) + +""" + +kei = r""" +Computes the Kelvin function kei, which for real arguments gives the +imaginary part of the (rescaled) Bessel K function of a rotated argument. +See :func:`~mpmath.ker`. +""" + +struveh = r""" +Gives the Struve function + +.. math :: + + \,\mathbf{H}_n(z) = + \sum_{k=0}^\infty \frac{(-1)^k}{\Gamma(k+\frac{3}{2}) + \Gamma(k+n+\frac{3}{2})} {\left({\frac{z}{2}}\right)}^{2k+n+1} + +which is a solution to the Struve differential equation + +.. math :: + + z^2 f''(z) + z f'(z) + (z^2-n^2) f(z) = \frac{2 z^{n+1}}{\pi (2n-1)!!}. + +**Examples** + +Evaluation for arbitrary real and complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> struveh(0, 3.5) + 0.3608207733778295024977797 + >>> struveh(-1, 10) + -0.255212719726956768034732 + >>> struveh(1, -100.5) + 0.5819566816797362287502246 + >>> struveh(2.5, 10000000000000) + 3153915652525200060.308937 + >>> struveh(2.5, -10000000000000) + (0.0 - 3153915652525200060.308937j) + >>> struveh(1+j, 1000000+4000000j) + (-3.066421087689197632388731e+1737173 - 1.596619701076529803290973e+1737173j) + +A Struve function of half-integer order is elementary; for example: + + >>> z = 3 + >>> struveh(0.5, 3) + 0.9167076867564138178671595 + >>> sqrt(2/(pi*z))*(1-cos(z)) + 0.9167076867564138178671595 + +Numerically verifying the differential equation:: + + >>> z = mpf(4.5) + >>> n = 3 + >>> f = lambda z: struveh(n,z) + >>> lhs = z**2*diff(f,z,2) + z*diff(f,z) + (z**2-n**2)*f(z) + >>> rhs = 2*z**(n+1)/fac2(2*n-1)/pi + >>> lhs + 17.40359302709875496632744 + >>> rhs + 17.40359302709875496632744 + +""" + +struvel = r""" +Gives the modified Struve function + +.. math :: + + \,\mathbf{L}_n(z) = -i e^{-n\pi i/2} \mathbf{H}_n(i z) + +which solves to the modified Struve differential equation + +.. math :: + + z^2 f''(z) + z f'(z) - (z^2+n^2) f(z) = \frac{2 z^{n+1}}{\pi (2n-1)!!}. + +**Examples** + +Evaluation for arbitrary real and complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> struvel(0, 3.5) + 7.180846515103737996249972 + >>> struvel(-1, 10) + 2670.994904980850550721511 + >>> struvel(1, -100.5) + 1.757089288053346261497686e+42 + >>> struvel(2.5, 10000000000000) + 4.160893281017115450519948e+4342944819025 + >>> struvel(2.5, -10000000000000) + (0.0 - 4.160893281017115450519948e+4342944819025j) + >>> struvel(1+j, 700j) + (-0.1721150049480079451246076 + 0.1240770953126831093464055j) + >>> struvel(1+j, 1000000+4000000j) + (-2.973341637511505389128708e+434290 - 5.164633059729968297147448e+434290j) + +Numerically verifying the differential equation:: + + >>> z = mpf(3.5) + >>> n = 3 + >>> f = lambda z: struvel(n,z) + >>> lhs = z**2*diff(f,z,2) + z*diff(f,z) - (z**2+n**2)*f(z) + >>> rhs = 2*z**(n+1)/fac2(2*n-1)/pi + >>> lhs + 6.368850306060678353018165 + >>> rhs + 6.368850306060678353018165 +""" + +appellf1 = r""" +Gives the Appell F1 hypergeometric function of two variables, + +.. math :: + + F_1(a,b_1,b_2,c,x,y) = \sum_{m=0}^{\infty} \sum_{n=0}^{\infty} + \frac{(a)_{m+n} (b_1)_m (b_2)_n}{(c)_{m+n}} + \frac{x^m y^n}{m! n!}. + +This series is only generally convergent when `|x| < 1` and `|y| < 1`, +although :func:`~mpmath.appellf1` can evaluate an analytic continuation +with respecto to either variable, and sometimes both. + +**Examples** + +Evaluation is supported for real and complex parameters:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> appellf1(1,0,0.5,1,0.5,0.25) + 1.154700538379251529018298 + >>> appellf1(1,1+j,0.5,1,0.5,0.5j) + (1.138403860350148085179415 + 1.510544741058517621110615j) + +For some integer parameters, the F1 series reduces to a polynomial:: + + >>> appellf1(2,-4,-3,1,2,5) + -816.0 + >>> appellf1(-5,1,2,1,4,5) + -20528.0 + +The analytic continuation with respect to either `x` or `y`, +and sometimes with respect to both, can be evaluated:: + + >>> appellf1(2,3,4,5,100,0.5) + (0.0006231042714165329279738662 + 0.0000005769149277148425774499857j) + >>> appellf1('1.1', '0.3', '0.2+2j', '0.4', '0.2', 1.5+3j) + (-0.1782604566893954897128702 + 0.002472407104546216117161499j) + >>> appellf1(1,2,3,4,10,12) + -0.07122993830066776374929313 + +For certain arguments, F1 reduces to an ordinary hypergeometric function:: + + >>> appellf1(1,2,3,5,0.5,0.25) + 1.547902270302684019335555 + >>> 4*hyp2f1(1,2,5,'1/3')/3 + 1.547902270302684019335555 + >>> appellf1(1,2,3,4,0,1.5) + (-1.717202506168937502740238 - 2.792526803190927323077905j) + >>> hyp2f1(1,3,4,1.5) + (-1.717202506168937502740238 - 2.792526803190927323077905j) + +The F1 function satisfies a system of partial differential equations:: + + >>> a,b1,b2,c,x,y = map(mpf, [1,0.5,0.25,1.125,0.25,-0.25]) + >>> F = lambda x,y: appellf1(a,b1,b2,c,x,y) + >>> chop(x*(1-x)*diff(F,(x,y),(2,0)) + + ... y*(1-x)*diff(F,(x,y),(1,1)) + + ... (c-(a+b1+1)*x)*diff(F,(x,y),(1,0)) - + ... b1*y*diff(F,(x,y),(0,1)) - + ... a*b1*F(x,y)) + 0.0 + >>> + >>> chop(y*(1-y)*diff(F,(x,y),(0,2)) + + ... x*(1-y)*diff(F,(x,y),(1,1)) + + ... (c-(a+b2+1)*y)*diff(F,(x,y),(0,1)) - + ... b2*x*diff(F,(x,y),(1,0)) - + ... a*b2*F(x,y)) + 0.0 + +The Appell F1 function allows for closed-form evaluation of various +integrals, such as any integral of the form +`\int x^r (x+a)^p (x+b)^q dx`:: + + >>> def integral(a,b,p,q,r,x1,x2): + ... a,b,p,q,r,x1,x2 = map(mpmathify, [a,b,p,q,r,x1,x2]) + ... f = lambda x: x**r * (x+a)**p * (x+b)**q + ... def F(x): + ... v = x**(r+1)/(r+1) * (a+x)**p * (b+x)**q + ... v *= (1+x/a)**(-p) + ... v *= (1+x/b)**(-q) + ... v *= appellf1(r+1,-p,-q,2+r,-x/a,-x/b) + ... return v + ... print("Num. quad: %s" % quad(f, [x1,x2])) + ... print("Appell F1: %s" % (F(x2)-F(x1))) + ... + >>> integral('1/5','4/3','-2','3','1/2',0,1) + Num. quad: 9.073335358785776206576981 + Appell F1: 9.073335358785776206576981 + >>> integral('3/2','4/3','-2','3','1/2',0,1) + Num. quad: 1.092829171999626454344678 + Appell F1: 1.092829171999626454344678 + >>> integral('3/2','4/3','-2','3','1/2',12,25) + Num. quad: 1106.323225040235116498927 + Appell F1: 1106.323225040235116498927 + +Also incomplete elliptic integrals fall into this category [1]:: + + >>> def E(z, m): + ... if (pi/2).ae(z): + ... return ellipe(m) + ... return 2*round(re(z)/pi)*ellipe(m) + mpf(-1)**round(re(z)/pi)*\ + ... sin(z)*appellf1(0.5,0.5,-0.5,1.5,sin(z)**2,m*sin(z)**2) + ... + >>> z, m = 1, 0.5 + >>> E(z,m); quad(lambda t: sqrt(1-m*sin(t)**2), [0,pi/4,3*pi/4,z]) + 0.9273298836244400669659042 + 0.9273298836244400669659042 + >>> z, m = 3, 2 + >>> E(z,m); quad(lambda t: sqrt(1-m*sin(t)**2), [0,pi/4,3*pi/4,z]) + (1.057495752337234229715836 + 1.198140234735592207439922j) + (1.057495752337234229715836 + 1.198140234735592207439922j) + +**References** + +1. [WolframFunctions]_ http://functions.wolfram.com/EllipticIntegrals/EllipticE2/26/01/ +2. [SrivastavaKarlsson]_ +3. [CabralRosetti]_ +4. [Vidunas]_ +5. [Slater]_ + +""" + +angerj = r""" +Gives the Anger function + +.. math :: + + \mathbf{J}_{\nu}(z) = \frac{1}{\pi} + \int_0^{\pi} \cos(\nu t - z \sin t) dt + +which is an entire function of both the parameter `\nu` and +the argument `z`. It solves the inhomogeneous Bessel differential +equation + +.. math :: + + f''(z) + \frac{1}{z}f'(z) + \left(1-\frac{\nu^2}{z^2}\right) f(z) + = \frac{(z-\nu)}{\pi z^2} \sin(\pi \nu). + +**Examples** + +Evaluation for real and complex parameter and argument:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> angerj(2,3) + 0.4860912605858910769078311 + >>> angerj(-3+4j, 2+5j) + (-5033.358320403384472395612 + 585.8011892476145118551756j) + >>> angerj(3.25, 1e6j) + (4.630743639715893346570743e+434290 - 1.117960409887505906848456e+434291j) + >>> angerj(-1.5, 1e6) + 0.0002795719747073879393087011 + +The Anger function coincides with the Bessel J-function when `\nu` +is an integer:: + + >>> angerj(1,3); besselj(1,3) + 0.3390589585259364589255146 + 0.3390589585259364589255146 + >>> angerj(1.5,3); besselj(1.5,3) + 0.4088969848691080859328847 + 0.4777182150870917715515015 + +Verifying the differential equation:: + + >>> v,z = mpf(2.25), 0.75 + >>> f = lambda z: angerj(v,z) + >>> diff(f,z,2) + diff(f,z)/z + (1-(v/z)**2)*f(z) + -0.6002108774380707130367995 + >>> (z-v)/(pi*z**2) * sinpi(v) + -0.6002108774380707130367995 + +Verifying the integral representation:: + + >>> angerj(v,z) + 0.1145380759919333180900501 + >>> quad(lambda t: cos(v*t-z*sin(t))/pi, [0,pi]) + 0.1145380759919333180900501 + +**References** + +1. [DLMF]_ section 11.10: Anger-Weber Functions +""" + +webere = r""" +Gives the Weber function + +.. math :: + + \mathbf{E}_{\nu}(z) = \frac{1}{\pi} + \int_0^{\pi} \sin(\nu t - z \sin t) dt + +which is an entire function of both the parameter `\nu` and +the argument `z`. It solves the inhomogeneous Bessel differential +equation + +.. math :: + + f''(z) + \frac{1}{z}f'(z) + \left(1-\frac{\nu^2}{z^2}\right) f(z) + = -\frac{1}{\pi z^2} (z+\nu+(z-\nu)\cos(\pi \nu)). + +**Examples** + +Evaluation for real and complex parameter and argument:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> webere(2,3) + -0.1057668973099018425662646 + >>> webere(-3+4j, 2+5j) + (-585.8081418209852019290498 - 5033.314488899926921597203j) + >>> webere(3.25, 1e6j) + (-1.117960409887505906848456e+434291 - 4.630743639715893346570743e+434290j) + >>> webere(3.25, 1e6) + -0.00002812518265894315604914453 + +Up to addition of a rational function of `z`, the Weber function coincides +with the Struve H-function when `\nu` is an integer:: + + >>> webere(1,3); 2/pi-struveh(1,3) + -0.3834897968188690177372881 + -0.3834897968188690177372881 + >>> webere(5,3); 26/(35*pi)-struveh(5,3) + 0.2009680659308154011878075 + 0.2009680659308154011878075 + +Verifying the differential equation:: + + >>> v,z = mpf(2.25), 0.75 + >>> f = lambda z: webere(v,z) + >>> diff(f,z,2) + diff(f,z)/z + (1-(v/z)**2)*f(z) + -1.097441848875479535164627 + >>> -(z+v+(z-v)*cospi(v))/(pi*z**2) + -1.097441848875479535164627 + +Verifying the integral representation:: + + >>> webere(v,z) + 0.1486507351534283744485421 + >>> quad(lambda t: sin(v*t-z*sin(t))/pi, [0,pi]) + 0.1486507351534283744485421 + +**References** + +1. [DLMF]_ section 11.10: Anger-Weber Functions +""" + +lommels1 = r""" +Gives the Lommel function `s_{\mu,\nu}` or `s^{(1)}_{\mu,\nu}` + +.. math :: + + s_{\mu,\nu}(z) = \frac{z^{\mu+1}}{(\mu-\nu+1)(\mu+\nu+1)} + \,_1F_2\left(1; \frac{\mu-\nu+3}{2}, \frac{\mu+\nu+3}{2}; + -\frac{z^2}{4} \right) + +which solves the inhomogeneous Bessel equation + +.. math :: + + z^2 f''(z) + z f'(z) + (z^2-\nu^2) f(z) = z^{\mu+1}. + +A second solution is given by :func:`~mpmath.lommels2`. + +**Plots** + +.. literalinclude :: /plots/lommels1.py +.. image :: /plots/lommels1.png + +**Examples** + +An integral representation:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> u,v,z = 0.25, 0.125, mpf(0.75) + >>> lommels1(u,v,z) + 0.4276243877565150372999126 + >>> (bessely(v,z)*quad(lambda t: t**u*besselj(v,t), [0,z]) - \ + ... besselj(v,z)*quad(lambda t: t**u*bessely(v,t), [0,z]))*(pi/2) + 0.4276243877565150372999126 + +A special value:: + + >>> lommels1(v,v,z) + 0.5461221367746048054932553 + >>> gamma(v+0.5)*sqrt(pi)*power(2,v-1)*struveh(v,z) + 0.5461221367746048054932553 + +Verifying the differential equation:: + + >>> f = lambda z: lommels1(u,v,z) + >>> z**2*diff(f,z,2) + z*diff(f,z) + (z**2-v**2)*f(z) + 0.6979536443265746992059141 + >>> z**(u+1) + 0.6979536443265746992059141 + +**References** + +1. [GradshteynRyzhik]_ +2. [Weisstein]_ http://mathworld.wolfram.com/LommelFunction.html +""" + +lommels2 = r""" +Gives the second Lommel function `S_{\mu,\nu}` or `s^{(2)}_{\mu,\nu}` + +.. math :: + + S_{\mu,\nu}(z) = s_{\mu,\nu}(z) + 2^{\mu-1} + \Gamma\left(\tfrac{1}{2}(\mu-\nu+1)\right) + \Gamma\left(\tfrac{1}{2}(\mu+\nu+1)\right) \times + + \left[\sin(\tfrac{1}{2}(\mu-\nu)\pi) J_{\nu}(z) - + \cos(\tfrac{1}{2}(\mu-\nu)\pi) Y_{\nu}(z) + \right] + +which solves the same differential equation as +:func:`~mpmath.lommels1`. + +**Plots** + +.. literalinclude :: /plots/lommels2.py +.. image :: /plots/lommels2.png + +**Examples** + +For large `|z|`, `S_{\mu,\nu} \sim z^{\mu-1}`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> lommels2(10,2,30000) + 1.968299831601008419949804e+40 + >>> power(30000,9) + 1.9683e+40 + +A special value:: + + >>> u,v,z = 0.5, 0.125, mpf(0.75) + >>> lommels2(v,v,z) + 0.9589683199624672099969765 + >>> (struveh(v,z)-bessely(v,z))*power(2,v-1)*sqrt(pi)*gamma(v+0.5) + 0.9589683199624672099969765 + +Verifying the differential equation:: + + >>> f = lambda z: lommels2(u,v,z) + >>> z**2*diff(f,z,2) + z*diff(f,z) + (z**2-v**2)*f(z) + 0.6495190528383289850727924 + >>> z**(u+1) + 0.6495190528383289850727924 + +**References** + +1. [GradshteynRyzhik]_ +2. [Weisstein]_ http://mathworld.wolfram.com/LommelFunction.html +""" + +appellf2 = r""" +Gives the Appell F2 hypergeometric function of two variables + +.. math :: + + F_2(a,b_1,b_2,c_1,c_2,x,y) = \sum_{m=0}^{\infty} \sum_{n=0}^{\infty} + \frac{(a)_{m+n} (b_1)_m (b_2)_n}{(c_1)_m (c_2)_n} + \frac{x^m y^n}{m! n!}. + +The series is generally absolutely convergent for `|x| + |y| < 1`. + +**Examples** + +Evaluation for real and complex arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> appellf2(1,2,3,4,5,0.25,0.125) + 1.257417193533135344785602 + >>> appellf2(1,-3,-4,2,3,2,3) + -42.8 + >>> appellf2(0.5,0.25,-0.25,2,3,0.25j,0.25) + (0.9880539519421899867041719 + 0.01497616165031102661476978j) + >>> chop(appellf2(1,1+j,1-j,3j,-3j,0.25,0.25)) + 1.201311219287411337955192 + >>> appellf2(1,1,1,4,6,0.125,16) + (-0.09455532250274744282125152 - 0.7647282253046207836769297j) + +A transformation formula:: + + >>> a,b1,b2,c1,c2,x,y = map(mpf, [1,2,0.5,0.25,1.625,-0.125,0.125]) + >>> appellf2(a,b1,b2,c1,c2,x,y) + 0.2299211717841180783309688 + >>> (1-x)**(-a)*appellf2(a,c1-b1,b2,c1,c2,x/(x-1),y/(1-x)) + 0.2299211717841180783309688 + +A system of partial differential equations satisfied by F2:: + + >>> a,b1,b2,c1,c2,x,y = map(mpf, [1,0.5,0.25,1.125,1.5,0.0625,-0.0625]) + >>> F = lambda x,y: appellf2(a,b1,b2,c1,c2,x,y) + >>> chop(x*(1-x)*diff(F,(x,y),(2,0)) - + ... x*y*diff(F,(x,y),(1,1)) + + ... (c1-(a+b1+1)*x)*diff(F,(x,y),(1,0)) - + ... b1*y*diff(F,(x,y),(0,1)) - + ... a*b1*F(x,y)) + 0.0 + >>> chop(y*(1-y)*diff(F,(x,y),(0,2)) - + ... x*y*diff(F,(x,y),(1,1)) + + ... (c2-(a+b2+1)*y)*diff(F,(x,y),(0,1)) - + ... b2*x*diff(F,(x,y),(1,0)) - + ... a*b2*F(x,y)) + 0.0 + +**References** + +See references for :func:`~mpmath.appellf1`. +""" + +appellf3 = r""" +Gives the Appell F3 hypergeometric function of two variables + +.. math :: + + F_3(a_1,a_2,b_1,b_2,c,x,y) = \sum_{m=0}^{\infty} \sum_{n=0}^{\infty} + \frac{(a_1)_m (a_2)_n (b_1)_m (b_2)_n}{(c)_{m+n}} + \frac{x^m y^n}{m! n!}. + +The series is generally absolutely convergent for `|x| < 1, |y| < 1`. + +**Examples** + +Evaluation for various parameters and variables:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> appellf3(1,2,3,4,5,0.5,0.25) + 2.221557778107438938158705 + >>> appellf3(1,2,3,4,5,6,0); hyp2f1(1,3,5,6) + (-0.5189554589089861284537389 - 0.1454441043328607980769742j) + (-0.5189554589089861284537389 - 0.1454441043328607980769742j) + >>> appellf3(1,-2,-3,1,1,4,6) + -17.4 + >>> appellf3(1,2,-3,1,1,4,6) + (17.7876136773677356641825 + 19.54768762233649126154534j) + >>> appellf3(1,2,-3,1,1,6,4) + (85.02054175067929402953645 + 148.4402528821177305173599j) + >>> chop(appellf3(1+j,2,1-j,2,3,0.25,0.25)) + 1.719992169545200286696007 + +Many transformations and evaluations for special combinations +of the parameters are possible, e.g.: + + >>> a,b,c,x,y = map(mpf, [0.5,0.25,0.125,0.125,-0.125]) + >>> appellf3(a,c-a,b,c-b,c,x,y) + 1.093432340896087107444363 + >>> (1-y)**(a+b-c)*hyp2f1(a,b,c,x+y-x*y) + 1.093432340896087107444363 + >>> x**2*appellf3(1,1,1,1,3,x,-x) + 0.01568646277445385390945083 + >>> polylog(2,x**2) + 0.01568646277445385390945083 + >>> a1,a2,b1,b2,c,x = map(mpf, [0.5,0.25,0.125,0.5,4.25,0.125]) + >>> appellf3(a1,a2,b1,b2,c,x,1) + 1.03947361709111140096947 + >>> gammaprod([c,c-a2-b2],[c-a2,c-b2])*hyp3f2(a1,b1,c-a2-b2,c-a2,c-b2,x) + 1.03947361709111140096947 + +The Appell F3 function satisfies a pair of partial +differential equations:: + + >>> a1,a2,b1,b2,c,x,y = map(mpf, [0.5,0.25,0.125,0.5,0.625,0.0625,-0.0625]) + >>> F = lambda x,y: appellf3(a1,a2,b1,b2,c,x,y) + >>> chop(x*(1-x)*diff(F,(x,y),(2,0)) + + ... y*diff(F,(x,y),(1,1)) + + ... (c-(a1+b1+1)*x)*diff(F,(x,y),(1,0)) - + ... a1*b1*F(x,y)) + 0.0 + >>> chop(y*(1-y)*diff(F,(x,y),(0,2)) + + ... x*diff(F,(x,y),(1,1)) + + ... (c-(a2+b2+1)*y)*diff(F,(x,y),(0,1)) - + ... a2*b2*F(x,y)) + 0.0 + +**References** + +See references for :func:`~mpmath.appellf1`. +""" + +appellf4 = r""" +Gives the Appell F4 hypergeometric function of two variables + +.. math :: + + F_4(a,b,c_1,c_2,x,y) = \sum_{m=0}^{\infty} \sum_{n=0}^{\infty} + \frac{(a)_{m+n} (b)_{m+n}}{(c_1)_m (c_2)_n} + \frac{x^m y^n}{m! n!}. + +The series is generally absolutely convergent for +`\sqrt{|x|} + \sqrt{|y|} < 1`. + +**Examples** + +Evaluation for various parameters and arguments:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> appellf4(1,1,2,2,0.25,0.125) + 1.286182069079718313546608 + >>> appellf4(-2,-3,4,5,4,5) + 34.8 + >>> appellf4(5,4,2,3,0.25j,-0.125j) + (-0.2585967215437846642163352 + 2.436102233553582711818743j) + +Reduction to `\,_2F_1` in a special case:: + + >>> a,b,c,x,y = map(mpf, [0.5,0.25,0.125,0.125,-0.125]) + >>> appellf4(a,b,c,a+b-c+1,x*(1-y),y*(1-x)) + 1.129143488466850868248364 + >>> hyp2f1(a,b,c,x)*hyp2f1(a,b,a+b-c+1,y) + 1.129143488466850868248364 + +A system of partial differential equations satisfied by F4:: + + >>> a,b,c1,c2,x,y = map(mpf, [1,0.5,0.25,1.125,0.0625,-0.0625]) + >>> F = lambda x,y: appellf4(a,b,c1,c2,x,y) + >>> chop(x*(1-x)*diff(F,(x,y),(2,0)) - + ... y**2*diff(F,(x,y),(0,2)) - + ... 2*x*y*diff(F,(x,y),(1,1)) + + ... (c1-(a+b+1)*x)*diff(F,(x,y),(1,0)) - + ... ((a+b+1)*y)*diff(F,(x,y),(0,1)) - + ... a*b*F(x,y)) + 0.0 + >>> chop(y*(1-y)*diff(F,(x,y),(0,2)) - + ... x**2*diff(F,(x,y),(2,0)) - + ... 2*x*y*diff(F,(x,y),(1,1)) + + ... (c2-(a+b+1)*y)*diff(F,(x,y),(0,1)) - + ... ((a+b+1)*x)*diff(F,(x,y),(1,0)) - + ... a*b*F(x,y)) + 0.0 + +**References** + +See references for :func:`~mpmath.appellf1`. +""" + +zeta = r""" +Computes the Riemann zeta function + +.. math :: + + \zeta(s) = 1+\frac{1}{2^s}+\frac{1}{3^s}+\frac{1}{4^s}+\ldots + +or, with `a \ne 1`, the more general Hurwitz zeta function + +.. math :: + + \zeta(s,a) = \sum_{k=0}^\infty \frac{1}{(a+k)^s}. + +Optionally, ``zeta(s, a, n)`` computes the `n`-th derivative with +respect to `s`, + +.. math :: + + \zeta^{(n)}(s,a) = (-1)^n \sum_{k=0}^\infty \frac{\log^n(a+k)}{(a+k)^s}. + +Although these series only converge for `\Re(s) > 1`, the Riemann and Hurwitz +zeta functions are defined through analytic continuation for arbitrary +complex `s \ne 1` (`s = 1` is a pole). + +The implementation uses three algorithms: the Borwein algorithm for +the Riemann zeta function when `s` is close to the real line; +the Riemann-Siegel formula for the Riemann zeta function when `s` is +large imaginary, and Euler-Maclaurin summation in all other cases. +The reflection formula for `\Re(s) < 0` is implemented in some cases. +The algorithm can be chosen with ``method = 'borwein'``, +``method='riemann-siegel'`` or ``method = 'euler-maclaurin'``. + +The parameter `a` is usually a rational number `a = p/q`, and may be specified +as such by passing an integer tuple `(p, q)`. Evaluation is supported for +arbitrary complex `a`, but may be slow and/or inaccurate when `\Re(s) < 0` for +nonrational `a` or when computing derivatives. + +**Examples** + +Some values of the Riemann zeta function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> zeta(2); pi**2 / 6 + 1.644934066848226436472415 + 1.644934066848226436472415 + >>> zeta(0) + -0.5 + >>> zeta(-1) + -0.08333333333333333333333333 + >>> zeta(-2) + 0.0 + +For large positive `s`, `\zeta(s)` rapidly approaches 1:: + + >>> zeta(50) + 1.000000000000000888178421 + >>> zeta(100) + 1.0 + >>> zeta(inf) + 1.0 + >>> 1-sum((zeta(k)-1)/k for k in range(2,85)); +euler + 0.5772156649015328606065121 + 0.5772156649015328606065121 + >>> nsum(lambda k: zeta(k)-1, [2, inf]) + 1.0 + +Evaluation is supported for complex `s` and `a`: + + >>> zeta(-3+4j) + (-0.03373057338827757067584698 + 0.2774499251557093745297677j) + >>> zeta(2+3j, -1+j) + (389.6841230140842816370741 + 295.2674610150305334025962j) + +The Riemann zeta function has so-called nontrivial zeros on +the critical line `s = 1/2 + it`:: + + >>> findroot(zeta, 0.5+14j); zetazero(1) + (0.5 + 14.13472514173469379045725j) + (0.5 + 14.13472514173469379045725j) + >>> findroot(zeta, 0.5+21j); zetazero(2) + (0.5 + 21.02203963877155499262848j) + (0.5 + 21.02203963877155499262848j) + >>> findroot(zeta, 0.5+25j); zetazero(3) + (0.5 + 25.01085758014568876321379j) + (0.5 + 25.01085758014568876321379j) + >>> chop(zeta(zetazero(10))) + 0.0 + +Evaluation on and near the critical line is supported for large +heights `t` by means of the Riemann-Siegel formula (currently +for `a = 1`, `n \le 4`):: + + >>> zeta(0.5+100000j) + (1.073032014857753132114076 + 5.780848544363503984261041j) + >>> zeta(0.75+1000000j) + (0.9535316058375145020351559 + 0.9525945894834273060175651j) + >>> zeta(0.5+10000000j) + (11.45804061057709254500227 - 8.643437226836021723818215j) + >>> zeta(0.5+100000000j, derivative=1) + (51.12433106710194942681869 + 43.87221167872304520599418j) + >>> zeta(0.5+100000000j, derivative=2) + (-444.2760822795430400549229 - 896.3789978119185981665403j) + >>> zeta(0.5+100000000j, derivative=3) + (3230.72682687670422215339 + 14374.36950073615897616781j) + >>> zeta(0.5+100000000j, derivative=4) + (-11967.35573095046402130602 - 218945.7817789262839266148j) + >>> zeta(1+10000000j) # off the line + (2.859846483332530337008882 + 0.491808047480981808903986j) + >>> zeta(1+10000000j, derivative=1) + (-4.333835494679647915673205 - 0.08405337962602933636096103j) + >>> zeta(1+10000000j, derivative=4) + (453.2764822702057701894278 - 581.963625832768189140995j) + +For investigation of the zeta function zeros, the Riemann-Siegel +Z-function is often more convenient than working with the Riemann +zeta function directly (see :func:`~mpmath.siegelz`). + +Some values of the Hurwitz zeta function:: + + >>> zeta(2, 3); -5./4 + pi**2/6 + 0.3949340668482264364724152 + 0.3949340668482264364724152 + >>> zeta(2, (3,4)); pi**2 - 8*catalan + 2.541879647671606498397663 + 2.541879647671606498397663 + +For positive integer values of `s`, the Hurwitz zeta function is +equivalent to a polygamma function (except for a normalizing factor):: + + >>> zeta(4, (1,5)); psi(3, '1/5')/6 + 625.5408324774542966919938 + 625.5408324774542966919938 + +Evaluation of derivatives:: + + >>> zeta(0, 3+4j, 1); loggamma(3+4j) - ln(2*pi)/2 + (-2.675565317808456852310934 + 4.742664438034657928194889j) + (-2.675565317808456852310934 + 4.742664438034657928194889j) + >>> zeta(2, 1, 20) + 2432902008176640000.000242 + >>> zeta(3+4j, 5.5+2j, 4) + (-0.140075548947797130681075 - 0.3109263360275413251313634j) + >>> zeta(0.5+100000j, 1, 4) + (-10407.16081931495861539236 + 13777.78669862804508537384j) + >>> zeta(-100+0.5j, (1,3), derivative=4) + (4.007180821099823942702249e+79 + 4.916117957092593868321778e+78j) + +Generating a Taylor series at `s = 2` using derivatives:: + + >>> for k in range(11): print("%s * (s-2)^%i" % (zeta(2,1,k)/fac(k), k)) + ... + 1.644934066848226436472415 * (s-2)^0 + -0.9375482543158437537025741 * (s-2)^1 + 0.9946401171494505117104293 * (s-2)^2 + -1.000024300473840810940657 * (s-2)^3 + 1.000061933072352565457512 * (s-2)^4 + -1.000006869443931806408941 * (s-2)^5 + 1.000000173233769531820592 * (s-2)^6 + -0.9999999569989868493432399 * (s-2)^7 + 0.9999999937218844508684206 * (s-2)^8 + -0.9999999996355013916608284 * (s-2)^9 + 1.000000000004610645020747 * (s-2)^10 + +Evaluation at zero and for negative integer `s`:: + + >>> zeta(0, 10) + -9.5 + >>> zeta(-2, (2,3)); mpf(1)/81 + 0.01234567901234567901234568 + 0.01234567901234567901234568 + >>> zeta(-3+4j, (5,4)) + (0.2899236037682695182085988 + 0.06561206166091757973112783j) + >>> zeta(-3.25, 1/pi) + -0.0005117269627574430494396877 + >>> zeta(-3.5, pi, 1) + 11.156360390440003294709 + >>> zeta(-100.5, (8,3)) + -4.68162300487989766727122e+77 + >>> zeta(-10.5, (-8,3)) + (-0.01521913704446246609237979 + 29907.72510874248161608216j) + >>> zeta(-1000.5, (-8,3)) + (1.031911949062334538202567e+1770 + 1.519555750556794218804724e+426j) + >>> zeta(-1+j, 3+4j) + (-16.32988355630802510888631 - 22.17706465801374033261383j) + >>> zeta(-1+j, 3+4j, 2) + (32.48985276392056641594055 - 51.11604466157397267043655j) + >>> diff(lambda s: zeta(s, 3+4j), -1+j, 2) + (32.48985276392056641594055 - 51.11604466157397267043655j) + +**References** + +1. http://mathworld.wolfram.com/RiemannZetaFunction.html + +2. http://mathworld.wolfram.com/HurwitzZetaFunction.html + +3. [BorweinZeta]_ + +""" + +dirichlet = r""" +Evaluates the Dirichlet L-function + +.. math :: + + L(s,\chi) = \sum_{k=1}^\infty \frac{\chi(k)}{k^s}. + +where `\chi` is a periodic sequence of length `q` which should be supplied +in the form of a list `[\chi(0), \chi(1), \ldots, \chi(q-1)]`. +Strictly, `\chi` should be a Dirichlet character, but any periodic +sequence will work. + +For example, ``dirichlet(s, [1])`` gives the ordinary +Riemann zeta function and ``dirichlet(s, [-1,1])`` gives +the alternating zeta function (Dirichlet eta function). + +Also the derivative with respect to `s` (currently only a first +derivative) can be evaluated. + +**Examples** + +The ordinary Riemann zeta function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> dirichlet(3, [1]); zeta(3) + 1.202056903159594285399738 + 1.202056903159594285399738 + >>> dirichlet(1, [1]) + +inf + +The alternating zeta function:: + + >>> dirichlet(1, [-1,1]); ln(2) + 0.6931471805599453094172321 + 0.6931471805599453094172321 + +The following defines the Dirichlet beta function +`\beta(s) = \sum_{k=0}^\infty \frac{(-1)^k}{(2k+1)^s}` and verifies +several values of this function:: + + >>> B = lambda s, d=0: dirichlet(s, [0, 1, 0, -1], d) + >>> B(0); 1./2 + 0.5 + 0.5 + >>> B(1); pi/4 + 0.7853981633974483096156609 + 0.7853981633974483096156609 + >>> B(2); +catalan + 0.9159655941772190150546035 + 0.9159655941772190150546035 + >>> B(2,1); diff(B, 2) + 0.08158073611659279510291217 + 0.08158073611659279510291217 + >>> B(-1,1); 2*catalan/pi + 0.5831218080616375602767689 + 0.5831218080616375602767689 + >>> B(0,1); log(gamma(0.25)**2/(2*pi*sqrt(2))) + 0.3915943927068367764719453 + 0.3915943927068367764719454 + >>> B(1,1); 0.25*pi*(euler+2*ln2+3*ln(pi)-4*ln(gamma(0.25))) + 0.1929013167969124293631898 + 0.1929013167969124293631898 + +A custom L-series of period 3:: + + >>> dirichlet(2, [2,0,1]) + 0.7059715047839078092146831 + >>> 2*nsum(lambda k: (3*k)**-2, [1,inf]) + \ + ... nsum(lambda k: (3*k+2)**-2, [0,inf]) + 0.7059715047839078092146831 + +""" + +coulombf = r""" +Calculates the regular Coulomb wave function + +.. math :: + + F_l(\eta,z) = C_l(\eta) z^{l+1} e^{-iz} \,_1F_1(l+1-i\eta, 2l+2, 2iz) + +where the normalization constant `C_l(\eta)` is as calculated by +:func:`~mpmath.coulombc`. This function solves the differential equation + +.. math :: + + f''(z) + \left(1-\frac{2\eta}{z}-\frac{l(l+1)}{z^2}\right) f(z) = 0. + +A second linearly independent solution is given by the irregular +Coulomb wave function `G_l(\eta,z)` (see :func:`~mpmath.coulombg`) +and thus the general solution is +`f(z) = C_1 F_l(\eta,z) + C_2 G_l(\eta,z)` for arbitrary +constants `C_1`, `C_2`. +Physically, the Coulomb wave functions give the radial solution +to the Schrodinger equation for a point particle in a `1/z` potential; `z` is +then the radius and `l`, `\eta` are quantum numbers. + +The Coulomb wave functions with real parameters are defined +in Abramowitz & Stegun, section 14. However, all parameters are permitted +to be complex in this implementation (see references). + +**Plots** + +.. literalinclude :: /plots/coulombf.py +.. image :: /plots/coulombf.png +.. literalinclude :: /plots/coulombf_c.py +.. image :: /plots/coulombf_c.png + +**Examples** + +Evaluation is supported for arbitrary magnitudes of `z`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> coulombf(2, 1.5, 3.5) + 0.4080998961088761187426445 + >>> coulombf(-2, 1.5, 3.5) + 0.7103040849492536747533465 + >>> coulombf(2, 1.5, '1e-10') + 4.143324917492256448770769e-33 + >>> coulombf(2, 1.5, 1000) + 0.4482623140325567050716179 + >>> coulombf(2, 1.5, 10**10) + -0.066804196437694360046619 + +Verifying the differential equation:: + + >>> l, eta, z = 2, 3, mpf(2.75) + >>> A, B = 1, 2 + >>> f = lambda z: A*coulombf(l,eta,z) + B*coulombg(l,eta,z) + >>> chop(diff(f,z,2) + (1-2*eta/z - l*(l+1)/z**2)*f(z)) + 0.0 + +A Wronskian relation satisfied by the Coulomb wave functions:: + + >>> l = 2 + >>> eta = 1.5 + >>> F = lambda z: coulombf(l,eta,z) + >>> G = lambda z: coulombg(l,eta,z) + >>> for z in [3.5, -1, 2+3j]: + ... chop(diff(F,z)*G(z) - F(z)*diff(G,z)) + ... + 1.0 + 1.0 + 1.0 + +Another Wronskian relation:: + + >>> F = coulombf + >>> G = coulombg + >>> for z in [3.5, -1, 2+3j]: + ... chop(F(l-1,eta,z)*G(l,eta,z)-F(l,eta,z)*G(l-1,eta,z) - l/sqrt(l**2+eta**2)) + ... + 0.0 + 0.0 + 0.0 + +An integral identity connecting the regular and irregular wave functions:: + + >>> l, eta, z = 4+j, 2-j, 5+2j + >>> coulombf(l,eta,z) + j*coulombg(l,eta,z) + (0.7997977752284033239714479 + 0.9294486669502295512503127j) + >>> g = lambda t: exp(-t)*t**(l-j*eta)*(t+2*j*z)**(l+j*eta) + >>> j*exp(-j*z)*z**(-l)/fac(2*l+1)/coulombc(l,eta)*quad(g, [0,inf]) + (0.7997977752284033239714479 + 0.9294486669502295512503127j) + +Some test case with complex parameters, taken from Michel [2]:: + + >>> mp.dps = 15 + >>> coulombf(1+0.1j, 50+50j, 100.156) + (-1.02107292320897e+15 - 2.83675545731519e+15j) + >>> coulombg(1+0.1j, 50+50j, 100.156) + (2.83675545731519e+15 - 1.02107292320897e+15j) + >>> coulombf(1e-5j, 10+1e-5j, 0.1+1e-6j) + (4.30566371247811e-14 - 9.03347835361657e-19j) + >>> coulombg(1e-5j, 10+1e-5j, 0.1+1e-6j) + (778709182061.134 + 18418936.2660553j) + +The following reproduces a table in Abramowitz & Stegun, at twice +the precision:: + + >>> mp.dps = 10 + >>> eta = 2; z = 5 + >>> for l in [5, 4, 3, 2, 1, 0]: + ... print("%s %s %s" % (l, coulombf(l,eta,z), + ... diff(lambda z: coulombf(l,eta,z), z))) + ... + 5 0.09079533488 0.1042553261 + 4 0.2148205331 0.2029591779 + 3 0.4313159311 0.320534053 + 2 0.7212774133 0.3952408216 + 1 0.9935056752 0.3708676452 + 0 1.143337392 0.2937960375 + +**References** + +1. I.J. Thompson & A.R. Barnett, "Coulomb and Bessel Functions of Complex + Arguments and Order", J. Comp. Phys., vol 64, no. 2, June 1986. + +2. N. Michel, "Precise Coulomb wave functions for a wide range of + complex `l`, `\eta` and `z`", http://arxiv.org/abs/physics/0702051v1 + +""" + +coulombg = r""" +Calculates the irregular Coulomb wave function + +.. math :: + + G_l(\eta,z) = \frac{F_l(\eta,z) \cos(\chi) - F_{-l-1}(\eta,z)}{\sin(\chi)} + +where `\chi = \sigma_l - \sigma_{-l-1} - (l+1/2) \pi` +and `\sigma_l(\eta) = (\ln \Gamma(1+l+i\eta)-\ln \Gamma(1+l-i\eta))/(2i)`. + +See :func:`~mpmath.coulombf` for additional information. + +**Plots** + +.. literalinclude :: /plots/coulombg.py +.. image :: /plots/coulombg.png +.. literalinclude :: /plots/coulombg_c.py +.. image :: /plots/coulombg_c.png + +**Examples** + +Evaluation is supported for arbitrary magnitudes of `z`:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> coulombg(-2, 1.5, 3.5) + 1.380011900612186346255524 + >>> coulombg(2, 1.5, 3.5) + 1.919153700722748795245926 + >>> coulombg(-2, 1.5, '1e-10') + 201126715824.7329115106793 + >>> coulombg(-2, 1.5, 1000) + 0.1802071520691149410425512 + >>> coulombg(-2, 1.5, 10**10) + 0.652103020061678070929794 + +The following reproduces a table in Abramowitz & Stegun, +at twice the precision:: + + >>> mp.dps = 10 + >>> eta = 2; z = 5 + >>> for l in [1, 2, 3, 4, 5]: + ... print("%s %s %s" % (l, coulombg(l,eta,z), + ... -diff(lambda z: coulombg(l,eta,z), z))) + ... + 1 1.08148276 0.6028279961 + 2 1.496877075 0.5661803178 + 3 2.048694714 0.7959909551 + 4 3.09408669 1.731802374 + 5 5.629840456 4.549343289 + +Evaluation close to the singularity at `z = 0`:: + + >>> mp.dps = 15 + >>> coulombg(0,10,1) + 3088184933.67358 + >>> coulombg(0,10,'1e-10') + 5554866000719.8 + >>> coulombg(0,10,'1e-100') + 5554866221524.1 + +Evaluation with a half-integer value for `l`:: + + >>> coulombg(1.5, 1, 10) + 0.852320038297334 +""" + +coulombc = r""" +Gives the normalizing Gamow constant for Coulomb wave functions, + +.. math :: + + C_l(\eta) = 2^l \exp\left(-\pi \eta/2 + [\ln \Gamma(1+l+i\eta) + + \ln \Gamma(1+l-i\eta)]/2 - \ln \Gamma(2l+2)\right), + +where the log gamma function with continuous imaginary part +away from the negative half axis (see :func:`~mpmath.loggamma`) is implied. + +This function is used internally for the calculation of +Coulomb wave functions, and automatically cached to make multiple +evaluations with fixed `l`, `\eta` fast. +""" + +ellipfun = r""" +Computes any of the Jacobi elliptic functions, defined +in terms of Jacobi theta functions as + +.. math :: + + \mathrm{sn}(u,m) = \frac{\vartheta_3(0,q)}{\vartheta_2(0,q)} + \frac{\vartheta_1(t,q)}{\vartheta_4(t,q)} + + \mathrm{cn}(u,m) = \frac{\vartheta_4(0,q)}{\vartheta_2(0,q)} + \frac{\vartheta_2(t,q)}{\vartheta_4(t,q)} + + \mathrm{dn}(u,m) = \frac{\vartheta_4(0,q)}{\vartheta_3(0,q)} + \frac{\vartheta_3(t,q)}{\vartheta_4(t,q)}, + +or more generally computes a ratio of two such functions. Here +`t = u/\vartheta_3(0,q)^2`, and `q = q(m)` denotes the nome (see +:func:`~mpmath.nome`). Optionally, you can specify the nome directly +instead of `m` by passing ``q=``, or you can directly +specify the elliptic parameter `k` with ``k=``. + +The first argument should be a two-character string specifying the +function using any combination of ``'s'``, ``'c'``, ``'d'``, ``'n'``. These +letters respectively denote the basic functions +`\mathrm{sn}(u,m)`, `\mathrm{cn}(u,m)`, `\mathrm{dn}(u,m)`, and `1`. +The identifier specifies the ratio of two such functions. +For example, ``'ns'`` identifies the function + +.. math :: + + \mathrm{ns}(u,m) = \frac{1}{\mathrm{sn}(u,m)} + +and ``'cd'`` identifies the function + +.. math :: + + \mathrm{cd}(u,m) = \frac{\mathrm{cn}(u,m)}{\mathrm{dn}(u,m)}. + +If called with only the first argument, a function object +evaluating the chosen function for given arguments is returned. + +**Examples** + +Basic evaluation:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> ellipfun('cd', 3.5, 0.5) + -0.9891101840595543931308394 + >>> ellipfun('cd', 3.5, q=0.25) + 0.07111979240214668158441418 + +The sn-function is doubly periodic in the complex plane with periods +`4 K(m)` and `2 i K(1-m)` (see :func:`~mpmath.ellipk`):: + + >>> sn = ellipfun('sn') + >>> sn(2, 0.25) + 0.9628981775982774425751399 + >>> sn(2+4*ellipk(0.25), 0.25) + 0.9628981775982774425751399 + >>> chop(sn(2+2*j*ellipk(1-0.25), 0.25)) + 0.9628981775982774425751399 + +The cn-function is doubly periodic with periods `4 K(m)` and `2 K(m) + 2 i K(1-m)`:: + + >>> cn = ellipfun('cn') + >>> cn(2, 0.25) + -0.2698649654510865792581416 + >>> cn(2+4*ellipk(0.25), 0.25) + -0.2698649654510865792581416 + >>> chop(cn(2+2*ellipk(0.25)+2*j*ellipk(1-0.25), 0.25)) + -0.2698649654510865792581416 + +The dn-function is doubly periodic with periods `2 K(m)` and `4 i K(1-m)`:: + + >>> dn = ellipfun('dn') + >>> dn(2, 0.25) + 0.8764740583123262286931578 + >>> dn(2+2*ellipk(0.25), 0.25) + 0.8764740583123262286931578 + >>> chop(dn(2+4*j*ellipk(1-0.25), 0.25)) + 0.8764740583123262286931578 + +""" + + +jtheta = r""" +Computes the Jacobi theta function `\vartheta_n(z, q)`, where +`n = 1, 2, 3, 4`, defined by the infinite series: + +.. math :: + + \vartheta_1(z,q) = 2 q^{1/4} \sum_{n=0}^{\infty} + (-1)^n q^{n^2+n\,} \sin((2n+1)z) + + \vartheta_2(z,q) = 2 q^{1/4} \sum_{n=0}^{\infty} + q^{n^{2\,} + n} \cos((2n+1)z) + + \vartheta_3(z,q) = 1 + 2 \sum_{n=1}^{\infty} + q^{n^2\,} \cos(2 n z) + + \vartheta_4(z,q) = 1 + 2 \sum_{n=1}^{\infty} + (-q)^{n^2\,} \cos(2 n z) + +The theta functions are functions of two variables: + +* `z` is the *argument*, an arbitrary real or complex number + +* `q` is the *nome*, which must be a real or complex number + in the unit disk (i.e. `|q| < 1`). For `|q| \ll 1`, the + series converge very quickly, so the Jacobi theta functions + can efficiently be evaluated to high precision. + +The compact notations `\vartheta_n(q) = \vartheta_n(0,q)` +and `\vartheta_n = \vartheta_n(0,q)` are also frequently +encountered. Finally, Jacobi theta functions are frequently +considered as functions of the half-period ratio `\tau` +and then usually denoted by `\vartheta_n(z|\tau)`. + +Optionally, ``jtheta(n, z, q, derivative=d)`` with `d > 0` computes +a `d`-th derivative with respect to `z`. + +**Examples and basic properties** + +Considered as functions of `z`, the Jacobi theta functions may be +viewed as generalizations of the ordinary trigonometric functions +cos and sin. They are periodic functions:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> jtheta(1, 0.25, '0.2') + 0.2945120798627300045053104 + >>> jtheta(1, 0.25 + 2*pi, '0.2') + 0.2945120798627300045053104 + +Indeed, the series defining the theta functions are essentially +trigonometric Fourier series. The coefficients can be retrieved +using :func:`~mpmath.fourier`:: + + >>> mp.dps = 10 + >>> nprint(fourier(lambda x: jtheta(2, x, 0.5), [-pi, pi], 4)) + ([0.0, 1.68179, 0.0, 0.420448, 0.0], [0.0, 0.0, 0.0, 0.0, 0.0]) + +The Jacobi theta functions are also so-called quasiperiodic +functions of `z` and `\tau`, meaning that for fixed `\tau`, +`\vartheta_n(z, q)` and `\vartheta_n(z+\pi \tau, q)` are the same +except for an exponential factor:: + + >>> mp.dps = 25 + >>> tau = 3*j/10 + >>> q = exp(pi*j*tau) + >>> z = 10 + >>> jtheta(4, z+tau*pi, q) + (-0.682420280786034687520568 + 1.526683999721399103332021j) + >>> -exp(-2*j*z)/q * jtheta(4, z, q) + (-0.682420280786034687520568 + 1.526683999721399103332021j) + +The Jacobi theta functions satisfy a huge number of other +functional equations, such as the following identity (valid for +any `q`):: + + >>> q = mpf(3)/10 + >>> jtheta(3,0,q)**4 + 6.823744089352763305137427 + >>> jtheta(2,0,q)**4 + jtheta(4,0,q)**4 + 6.823744089352763305137427 + +Extensive listings of identities satisfied by the Jacobi theta +functions can be found in standard reference works. + +The Jacobi theta functions are related to the gamma function +for special arguments:: + + >>> jtheta(3, 0, exp(-pi)) + 1.086434811213308014575316 + >>> pi**(1/4.) / gamma(3/4.) + 1.086434811213308014575316 + +:func:`~mpmath.jtheta` supports arbitrary precision evaluation and complex +arguments:: + + >>> mp.dps = 50 + >>> jtheta(4, sqrt(2), 0.5) + 2.0549510717571539127004115835148878097035750653737 + >>> mp.dps = 25 + >>> jtheta(4, 1+2j, (1+j)/5) + (7.180331760146805926356634 - 1.634292858119162417301683j) + +Evaluation of derivatives:: + + >>> mp.dps = 25 + >>> jtheta(1, 7, 0.25, 1); diff(lambda z: jtheta(1, z, 0.25), 7) + 1.209857192844475388637236 + 1.209857192844475388637236 + >>> jtheta(1, 7, 0.25, 2); diff(lambda z: jtheta(1, z, 0.25), 7, 2) + -0.2598718791650217206533052 + -0.2598718791650217206533052 + >>> jtheta(2, 7, 0.25, 1); diff(lambda z: jtheta(2, z, 0.25), 7) + -1.150231437070259644461474 + -1.150231437070259644461474 + >>> jtheta(2, 7, 0.25, 2); diff(lambda z: jtheta(2, z, 0.25), 7, 2) + -0.6226636990043777445898114 + -0.6226636990043777445898114 + >>> jtheta(3, 7, 0.25, 1); diff(lambda z: jtheta(3, z, 0.25), 7) + -0.9990312046096634316587882 + -0.9990312046096634316587882 + >>> jtheta(3, 7, 0.25, 2); diff(lambda z: jtheta(3, z, 0.25), 7, 2) + -0.1530388693066334936151174 + -0.1530388693066334936151174 + >>> jtheta(4, 7, 0.25, 1); diff(lambda z: jtheta(4, z, 0.25), 7) + 0.9820995967262793943571139 + 0.9820995967262793943571139 + >>> jtheta(4, 7, 0.25, 2); diff(lambda z: jtheta(4, z, 0.25), 7, 2) + 0.3936902850291437081667755 + 0.3936902850291437081667755 + +**Possible issues** + +For `|q| \ge 1` or `\Im(\tau) \le 0`, :func:`~mpmath.jtheta` raises +``ValueError``. This exception is also raised for `|q|` extremely +close to 1 (or equivalently `\tau` very close to 0), since the +series would converge too slowly:: + + >>> jtheta(1, 10, 0.99999999 * exp(0.5*j)) + Traceback (most recent call last): + ... + ValueError: abs(q) > THETA_Q_LIM = 1.000000 + +""" + +eulernum = r""" +Gives the `n`-th Euler number, defined as the `n`-th derivative of +`\mathrm{sech}(t) = 1/\cosh(t)` evaluated at `t = 0`. Equivalently, the +Euler numbers give the coefficients of the Taylor series + +.. math :: + + \mathrm{sech}(t) = \sum_{n=0}^{\infty} \frac{E_n}{n!} t^n. + +The Euler numbers are closely related to Bernoulli numbers +and Bernoulli polynomials. They can also be evaluated in terms of +Euler polynomials (see :func:`~mpmath.eulerpoly`) as `E_n = 2^n E_n(1/2)`. + +**Examples** + +Computing the first few Euler numbers and verifying that they +agree with the Taylor series:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> [eulernum(n) for n in range(11)] + [1.0, 0.0, -1.0, 0.0, 5.0, 0.0, -61.0, 0.0, 1385.0, 0.0, -50521.0] + >>> chop(diffs(sech, 0, 10)) + [1.0, 0.0, -1.0, 0.0, 5.0, 0.0, -61.0, 0.0, 1385.0, 0.0, -50521.0] + +Euler numbers grow very rapidly. :func:`~mpmath.eulernum` efficiently +computes numerical approximations for large indices:: + + >>> eulernum(50) + -6.053285248188621896314384e+54 + >>> eulernum(1000) + 3.887561841253070615257336e+2371 + >>> eulernum(10**20) + 4.346791453661149089338186e+1936958564106659551331 + +Comparing with an asymptotic formula for the Euler numbers:: + + >>> n = 10**5 + >>> (-1)**(n//2) * 8 * sqrt(n/(2*pi)) * (2*n/(pi*e))**n + 3.69919063017432362805663e+436961 + >>> eulernum(n) + 3.699193712834466537941283e+436961 + +Pass ``exact=True`` to obtain exact values of Euler numbers as integers:: + + >>> print(eulernum(50, exact=True)) + -6053285248188621896314383785111649088103498225146815121 + >>> print(eulernum(200, exact=True) % 10**10) + 1925859625 + >>> eulernum(1001, exact=True) + 0 +""" + +eulerpoly = r""" +Evaluates the Euler polynomial `E_n(z)`, defined by the generating function +representation + +.. math :: + + \frac{2e^{zt}}{e^t+1} = \sum_{n=0}^\infty E_n(z) \frac{t^n}{n!}. + +The Euler polynomials may also be represented in terms of +Bernoulli polynomials (see :func:`~mpmath.bernpoly`) using various formulas, for +example + +.. math :: + + E_n(z) = \frac{2}{n+1} \left( + B_n(z)-2^{n+1}B_n\left(\frac{z}{2}\right) + \right). + +Special values include the Euler numbers `E_n = 2^n E_n(1/2)` (see +:func:`~mpmath.eulernum`). + +**Examples** + +Computing the coefficients of the first few Euler polynomials:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> for n in range(6): + ... chop(taylor(lambda z: eulerpoly(n,z), 0, n)) + ... + [1.0] + [-0.5, 1.0] + [0.0, -1.0, 1.0] + [0.25, 0.0, -1.5, 1.0] + [0.0, 1.0, 0.0, -2.0, 1.0] + [-0.5, 0.0, 2.5, 0.0, -2.5, 1.0] + +Evaluation for arbitrary `z`:: + + >>> eulerpoly(2,3) + 6.0 + >>> eulerpoly(5,4) + 423.5 + >>> eulerpoly(35, 11111111112) + 3.994957561486776072734601e+351 + >>> eulerpoly(4, 10+20j) + (-47990.0 - 235980.0j) + >>> eulerpoly(2, '-3.5e-5') + 0.000035001225 + >>> eulerpoly(3, 0.5) + 0.0 + >>> eulerpoly(55, -10**80) + -1.0e+4400 + >>> eulerpoly(5, -inf) + -inf + >>> eulerpoly(6, -inf) + +inf + +Computing Euler numbers:: + + >>> 2**26 * eulerpoly(26,0.5) + -4087072509293123892361.0 + >>> eulernum(26) + -4087072509293123892361.0 + +Evaluation is accurate for large `n` and small `z`:: + + >>> eulerpoly(100, 0.5) + 2.29047999988194114177943e+108 + >>> eulerpoly(1000, 10.5) + 3.628120031122876847764566e+2070 + >>> eulerpoly(10000, 10.5) + 1.149364285543783412210773e+30688 +""" + +spherharm = r""" +Evaluates the spherical harmonic `Y_l^m(\theta,\phi)`, + +.. math :: + + Y_l^m(\theta,\phi) = \sqrt{\frac{2l+1}{4\pi}\frac{(l-m)!}{(l+m)!}} + P_l^m(\cos \theta) e^{i m \phi} + +where `P_l^m` is an associated Legendre function (see :func:`~mpmath.legenp`). + +Here `\theta \in [0, \pi]` denotes the polar coordinate (ranging +from the north pole to the south pole) and `\phi \in [0, 2 \pi]` denotes the +azimuthal coordinate on a sphere. Care should be used since many different +conventions for spherical coordinate variables are used. + +Usually spherical harmonics are considered for `l \in \mathbb{N}`, +`m \in \mathbb{Z}`, `|m| \le l`. More generally, `l,m,\theta,\phi` +are permitted to be complex numbers. + +.. note :: + + :func:`~mpmath.spherharm` returns a complex number, even if the value is + purely real. + +**Plots** + +.. literalinclude :: /plots/spherharm40.py + +`Y_{4,0}`: + +.. image :: /plots/spherharm40.png + +`Y_{4,1}`: + +.. image :: /plots/spherharm41.png + +`Y_{4,2}`: + +.. image :: /plots/spherharm42.png + +`Y_{4,3}`: + +.. image :: /plots/spherharm43.png + +`Y_{4,4}`: + +.. image :: /plots/spherharm44.png + +**Examples** + +Some low-order spherical harmonics with reference values:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> theta = pi/4 + >>> phi = pi/3 + >>> spherharm(0,0,theta,phi); 0.5*sqrt(1/pi)*expj(0) + (0.2820947917738781434740397 + 0.0j) + (0.2820947917738781434740397 + 0.0j) + >>> spherharm(1,-1,theta,phi); 0.5*sqrt(3/(2*pi))*expj(-phi)*sin(theta) + (0.1221506279757299803965962 - 0.2115710938304086076055298j) + (0.1221506279757299803965962 - 0.2115710938304086076055298j) + >>> spherharm(1,0,theta,phi); 0.5*sqrt(3/pi)*cos(theta)*expj(0) + (0.3454941494713354792652446 + 0.0j) + (0.3454941494713354792652446 + 0.0j) + >>> spherharm(1,1,theta,phi); -0.5*sqrt(3/(2*pi))*expj(phi)*sin(theta) + (-0.1221506279757299803965962 - 0.2115710938304086076055298j) + (-0.1221506279757299803965962 - 0.2115710938304086076055298j) + +With the normalization convention used, the spherical harmonics are orthonormal +on the unit sphere:: + + >>> sphere = [0,pi], [0,2*pi] + >>> dS = lambda t,p: fp.sin(t) # differential element + >>> Y1 = lambda t,p: fp.spherharm(l1,m1,t,p) + >>> Y2 = lambda t,p: fp.conj(fp.spherharm(l2,m2,t,p)) + >>> l1 = l2 = 3; m1 = m2 = 2 + >>> fp.chop(fp.quad(lambda t,p: Y1(t,p)*Y2(t,p)*dS(t,p), *sphere)) + 1.0000000000000007 + >>> m2 = 1 # m1 != m2 + >>> print(fp.chop(fp.quad(lambda t,p: Y1(t,p)*Y2(t,p)*dS(t,p), *sphere))) + 0.0 + +Evaluation is accurate for large orders:: + + >>> spherharm(1000,750,0.5,0.25) + (3.776445785304252879026585e-102 - 5.82441278771834794493484e-102j) + +Evaluation works with complex parameter values:: + + >>> spherharm(1+j, 2j, 2+3j, -0.5j) + (64.44922331113759992154992 + 1981.693919841408089681743j) +""" + +scorergi = r""" +Evaluates the Scorer function + +.. math :: + + \operatorname{Gi}(z) = + \operatorname{Ai}(z) \int_0^z \operatorname{Bi}(t) dt + + \operatorname{Bi}(z) \int_z^{\infty} \operatorname{Ai}(t) dt + +which gives a particular solution to the inhomogeneous Airy +differential equation `f''(z) - z f(z) = 1/\pi`. Another +particular solution is given by the Scorer Hi-function +(:func:`~mpmath.scorerhi`). The two functions are related as +`\operatorname{Gi}(z) + \operatorname{Hi}(z) = \operatorname{Bi}(z)`. + +**Plots** + +.. literalinclude :: /plots/gi.py +.. image :: /plots/gi.png +.. literalinclude :: /plots/gi_c.py +.. image :: /plots/gi_c.png + +**Examples** + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> scorergi(0); 1/(power(3,'7/6')*gamma('2/3')) + 0.2049755424820002450503075 + 0.2049755424820002450503075 + >>> diff(scorergi, 0); 1/(power(3,'5/6')*gamma('1/3')) + 0.1494294524512754526382746 + 0.1494294524512754526382746 + >>> scorergi(+inf); scorergi(-inf) + 0.0 + 0.0 + >>> scorergi(1) + 0.2352184398104379375986902 + >>> scorergi(-1) + -0.1166722172960152826494198 + +Evaluation for large arguments:: + + >>> scorergi(10) + 0.03189600510067958798062034 + >>> scorergi(100) + 0.003183105228162961476590531 + >>> scorergi(1000000) + 0.0000003183098861837906721743873 + >>> 1/(pi*1000000) + 0.0000003183098861837906715377675 + >>> scorergi(-1000) + -0.08358288400262780392338014 + >>> scorergi(-100000) + 0.02886866118619660226809581 + >>> scorergi(50+10j) + (0.0061214102799778578790984 - 0.001224335676457532180747917j) + >>> scorergi(-50-10j) + (5.236047850352252236372551e+29 - 3.08254224233701381482228e+29j) + >>> scorergi(100000j) + (-8.806659285336231052679025e+6474077 + 8.684731303500835514850962e+6474077j) + +Verifying the connection between Gi and Hi:: + + >>> z = 0.25 + >>> scorergi(z) + scorerhi(z) + 0.7287469039362150078694543 + >>> airybi(z) + 0.7287469039362150078694543 + +Verifying the differential equation:: + + >>> for z in [-3.4, 0, 2.5, 1+2j]: + ... chop(diff(scorergi,z,2) - z*scorergi(z)) + ... + -0.3183098861837906715377675 + -0.3183098861837906715377675 + -0.3183098861837906715377675 + -0.3183098861837906715377675 + +Verifying the integral representation:: + + >>> z = 0.5 + >>> scorergi(z) + 0.2447210432765581976910539 + >>> Ai,Bi = airyai,airybi + >>> Bi(z)*(Ai(inf,-1)-Ai(z,-1)) + Ai(z)*(Bi(z,-1)-Bi(0,-1)) + 0.2447210432765581976910539 + +**References** + +1. [DLMF]_ section 9.12: Scorer Functions + +""" + +scorerhi = r""" +Evaluates the second Scorer function + +.. math :: + + \operatorname{Hi}(z) = + \operatorname{Bi}(z) \int_{-\infty}^z \operatorname{Ai}(t) dt - + \operatorname{Ai}(z) \int_{-\infty}^z \operatorname{Bi}(t) dt + +which gives a particular solution to the inhomogeneous Airy +differential equation `f''(z) - z f(z) = 1/\pi`. See also +:func:`~mpmath.scorergi`. + +**Plots** + +.. literalinclude :: /plots/hi.py +.. image :: /plots/hi.png +.. literalinclude :: /plots/hi_c.py +.. image :: /plots/hi_c.png + +**Examples** + +Some values and limits:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> scorerhi(0); 2/(power(3,'7/6')*gamma('2/3')) + 0.4099510849640004901006149 + 0.4099510849640004901006149 + >>> diff(scorerhi,0); 2/(power(3,'5/6')*gamma('1/3')) + 0.2988589049025509052765491 + 0.2988589049025509052765491 + >>> scorerhi(+inf); scorerhi(-inf) + +inf + 0.0 + >>> scorerhi(1) + 0.9722051551424333218376886 + >>> scorerhi(-1) + 0.2206696067929598945381098 + +Evaluation for large arguments:: + + >>> scorerhi(10) + 455641153.5163291358991077 + >>> scorerhi(100) + 6.041223996670201399005265e+288 + >>> scorerhi(1000000) + 7.138269638197858094311122e+289529652 + >>> scorerhi(-10) + 0.0317685352825022727415011 + >>> scorerhi(-100) + 0.003183092495767499864680483 + >>> scorerhi(100j) + (-6.366197716545672122983857e-9 + 0.003183098861710582761688475j) + >>> scorerhi(50+50j) + (-5.322076267321435669290334e+63 + 1.478450291165243789749427e+65j) + >>> scorerhi(-1000-1000j) + (0.0001591549432510502796565538 - 0.000159154943091895334973109j) + +Verifying the differential equation:: + + >>> for z in [-3.4, 0, 2, 1+2j]: + ... chop(diff(scorerhi,z,2) - z*scorerhi(z)) + ... + 0.3183098861837906715377675 + 0.3183098861837906715377675 + 0.3183098861837906715377675 + 0.3183098861837906715377675 + +Verifying the integral representation:: + + >>> z = 0.5 + >>> scorerhi(z) + 0.6095559998265972956089949 + >>> Ai,Bi = airyai,airybi + >>> Bi(z)*(Ai(z,-1)-Ai(-inf,-1)) - Ai(z)*(Bi(z,-1)-Bi(-inf,-1)) + 0.6095559998265972956089949 + +""" + + +stirling1 = r""" +Gives the Stirling number of the first kind `s(n,k)`, defined by + +.. math :: + + x(x-1)(x-2)\cdots(x-n+1) = \sum_{k=0}^n s(n,k) x^k. + +The value is computed using an integer recurrence. The implementation +is not optimized for approximating large values quickly. + +**Examples** + +Comparing with the generating function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> taylor(lambda x: ff(x, 5), 0, 5) + [0.0, 24.0, -50.0, 35.0, -10.0, 1.0] + >>> [stirling1(5, k) for k in range(6)] + [0.0, 24.0, -50.0, 35.0, -10.0, 1.0] + +Recurrence relation:: + + >>> n, k = 5, 3 + >>> stirling1(n+1,k) + n*stirling1(n,k) - stirling1(n,k-1) + 0.0 + +The matrices of Stirling numbers of first and second kind are inverses +of each other:: + + >>> A = matrix(5, 5); B = matrix(5, 5) + >>> for n in range(5): + ... for k in range(5): + ... A[n,k] = stirling1(n,k) + ... B[n,k] = stirling2(n,k) + ... + >>> A * B + [1.0 0.0 0.0 0.0 0.0] + [0.0 1.0 0.0 0.0 0.0] + [0.0 0.0 1.0 0.0 0.0] + [0.0 0.0 0.0 1.0 0.0] + [0.0 0.0 0.0 0.0 1.0] + +Pass ``exact=True`` to obtain exact values of Stirling numbers as integers:: + + >>> stirling1(42, 5) + -2.864498971768501633736628e+50 + >>> print(stirling1(42, 5, exact=True)) + -286449897176850163373662803014001546235808317440000 + +""" + +stirling2 = r""" +Gives the Stirling number of the second kind `S(n,k)`, defined by + +.. math :: + + x^n = \sum_{k=0}^n S(n,k) x(x-1)(x-2)\cdots(x-k+1) + +The value is computed using integer arithmetic to evaluate a power sum. +The implementation is not optimized for approximating large values quickly. + +**Examples** + +Comparing with the generating function:: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> taylor(lambda x: sum(stirling2(5,k) * ff(x,k) for k in range(6)), 0, 5) + [0.0, 0.0, 0.0, 0.0, 0.0, 1.0] + +Recurrence relation:: + + >>> n, k = 5, 3 + >>> stirling2(n+1,k) - k*stirling2(n,k) - stirling2(n,k-1) + 0.0 + +Pass ``exact=True`` to obtain exact values of Stirling numbers as integers:: + + >>> stirling2(52, 10) + 2.641822121003543906807485e+45 + >>> print(stirling2(52, 10, exact=True)) + 2641822121003543906807485307053638921722527655 + + +""" + +squarew = r""" +Computes the square wave function using the definition: + +.. math:: + x(t) = A(-1)^{\left\lfloor{2t / P}\right\rfloor} + +where `P` is the period of the wave and `A` is the amplitude. + +**Examples** + +Square wave with period = 2, amplitude = 1 :: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> squarew(0,1,2) + 1.0 + >>> squarew(0.5,1,2) + 1.0 + >>> squarew(1,1,2) + -1.0 + >>> squarew(1.5,1,2) + -1.0 + >>> squarew(2,1,2) + 1.0 +""" + +trianglew = r""" +Computes the triangle wave function using the definition: + +.. math:: + x(t) = 2A\left(\frac{1}{2}-\left|1-2 \operatorname{frac}\left(\frac{x}{P}+\frac{1}{4}\right)\right|\right) + +where :math:`\operatorname{frac}\left(\frac{t}{T}\right) = \frac{t}{T}-\left\lfloor{\frac{t}{T}}\right\rfloor` +, `P` is the period of the wave, and `A` is the amplitude. + +**Examples** + +Triangle wave with period = 2, amplitude = 1 :: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> trianglew(0,1,2) + 0.0 + >>> trianglew(0.25,1,2) + 0.5 + >>> trianglew(0.5,1,2) + 1.0 + >>> trianglew(1,1,2) + 0.0 + >>> trianglew(1.5,1,2) + -1.0 + >>> trianglew(2,1,2) + 0.0 +""" + +sawtoothw = r""" +Computes the sawtooth wave function using the definition: + +.. math:: + x(t) = A\operatorname{frac}\left(\frac{t}{T}\right) + +where :math:`\operatorname{frac}\left(\frac{t}{T}\right) = \frac{t}{T}-\left\lfloor{\frac{t}{T}}\right\rfloor`, +`P` is the period of the wave, and `A` is the amplitude. + +**Examples** + +Sawtooth wave with period = 2, amplitude = 1 :: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> sawtoothw(0,1,2) + 0.0 + >>> sawtoothw(0.5,1,2) + 0.25 + >>> sawtoothw(1,1,2) + 0.5 + >>> sawtoothw(1.5,1,2) + 0.75 + >>> sawtoothw(2,1,2) + 0.0 +""" + +unit_triangle = r""" +Computes the unit triangle using the definition: + +.. math:: + x(t) = A(-\left| t \right| + 1) + +where `A` is the amplitude. + +**Examples** + +Unit triangle with amplitude = 1 :: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> unit_triangle(-1,1) + 0.0 + >>> unit_triangle(-0.5,1) + 0.5 + >>> unit_triangle(0,1) + 1.0 + >>> unit_triangle(0.5,1) + 0.5 + >>> unit_triangle(1,1) + 0.0 +""" + +sigmoid = r""" +Computes the sigmoid function using the definition: + +.. math:: + x(t) = \frac{A}{1 + e^{-t}} + +where `A` is the amplitude. + +**Examples** + +Sigmoid function with amplitude = 1 :: + + >>> from mpmath import * + >>> mp.dps = 25; mp.pretty = True + >>> sigmoid(-1,1) + 0.2689414213699951207488408 + >>> sigmoid(-0.5,1) + 0.3775406687981454353610994 + >>> sigmoid(0,1) + 0.5 + >>> sigmoid(0.5,1) + 0.6224593312018545646389006 + >>> sigmoid(1,1) + 0.7310585786300048792511592 + +"""