[SciPy-dev] scipy.special.hyp2f1 bug?

[josef.pktd at gmail.com]

On Wed, Sep 16, 2009 at 9:02 PM, Skipper Seabold <jsseabold at gmail.com> wrote:
> Since y'all are looking at the distributions vs. mpmath, it reminded
> me of this.  I haven't filed a bug report yet, but I don't think one
> existed when I found this.
>
> I was working with the connection between the incomplete beta function
> and the hypergeometric2f1 function in scipy.special for GLM in
> statsmodels and I came across this blog post on mpmath about some
> corner cases for the hypergeometric2f1.
>
> <http://fredrik-j.blogspot.com/2009/06/hypergeometric-2f1-incomplete-beta.html>
>
> Two examples of discrepancies.
>
> In [1]: import mpmath
>
> In [2]: from scipy import special
>
> In [3]: mpmath.hyp2f1(3,-1,-1,0.5)
> Out[3]: mpf('2.5')
>
> In [4]: special.hyp2f1(3,-1,-1,.5)
> Out[4]: 8.0
>
> In [5]: mpmath.hyp2f1(1,1,4,3+4j)
> Out[5]: mpc(real='0.49234384000963544', imag='0.60513406166123973')
>
> In [6]: special.hyp2f1(1,1,4,3+4j)
> Out[6]: (0.65925460474847919+1.3277887264473263j)
>
> I will file a bug report shortly, if we think mpmath is correct vs. scipy.

there is a ticket for special.hyp2f1  for values that are used in rdist:

http://projects.scipy.org/scipy/ticket/759

but the parameter values in your case look different.

Josef

>
> -Skipper
> _______________________________________________
> Scipy-dev mailing list
> Scipy-dev at scipy.org
> http://mail.scipy.org/mailman/listinfo/scipy-dev
>