sympy/sympy — pull request #8092 by jksuom (2014-09-24 07:37:52+00:00)
Title: integrals: An amendment to spde()

The iterative version of `spde()` currently assumes that the
coefficient `a` of `Dp` were invariant in the loop, in which
case the values of the multiplier `alpha` are powers of `a`.
Otherwise the offset `beta` of the solution will be incorrect.

I have added two test cases where `a` is not invariant.
In the general case, `alpha` can be used instead of a power of `a`
to construct the correct value of `beta`.