numpy/numpy — pull request #5050 by juliantaylor (2014-09-05 19:11:16+00:00)
Title: ENH: add cube root function np.cbrt for real floats

wraps the C99 cube root function cbrt.
Compared to `np.power(x, 1./3.)` it is well defined for negative real
floats and is faster. `array**(1./3.)` now computes the cube root.

scalar**(1./3.) still calls power and is undefined for negative values.