[SciPy-Dev] [SciPy-User] polylogarithm?
Sat Sep 24 17:18:21 CDT 2011
For the record, I created a first pull request, with limited scope, in
order to make the C call to cephes described below possible. Further
I will switch to the dev list from now on.
On 09/23/2011 06:18 PM, Pauli Virtanen wrote:
> Fri, 23 Sep 2011 15:21:12 +0200, Johann Cohen-Tanugi wrote:
>> zetac(z) knows how to eat negative arguments, but not zeta(z,1).... Is
>> there a reason why special.zeta does not default to 1+special.zetac for
>> s=1? This would make the behavior of the 2 functions more identical.
> Probably no reason, except that it wasn't implemented. mpmath is
> impressive, and in several ways ahead of scipy.special --- or at least in
> the parts where the problems overlap, as you can do tricks with arbitrary
> precision that are not really feasible.
> Note that if you need to call the zeta function from the Cython extension,
> call the C library directly:
> cdef extern from "cephes.h":
> double zeta(double x, double q)
> double zetac(double x)
> and link the extension with the "sc_cephes" library.
> There's a formula (look in the mpmath sources ;) for the transform
> from x< 0 to x> 0 for zeta(x, a) for general a. But that needs polylog.
> The implementation for zetac(x) for x< 0 seems also a bit incomplete,
> as it goes only down to -30.8148. It seems this is due to a silly reason,
> it should use gammaln instead of Gamma to avoid the overflow.
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