Re: [Bug-gsl] gsl_sf_hyperg_2F1

[Brian Gough]

Olaf Wucknitz wrote:
> Hi,
>
> I am having a problem with gsl_sf_hyperg_2F1.
> With the parameters (-0.5, 0.5, 1, x) the returned values show a jump at 
> x=0.5. For x<0.5 the results seem to be correct, while for x>0.5 they 
> aren't.
> The function gsl_sf_hyperg_2F1_e calls hyperg_2F1_series for x<0.5, but
> hyperg_2F1_reflect for x>0.5. The latter function checks for c-a-b being 
> an integer (which it is in my case). If I change one of the parameters 
> a,b,c by a small amount, the other branch of the function is taken and the 
> results are correct again.
> Unfortunately I know too little about the numerics of 2F1 to suggest a 
> patch at the moment.

Hello,
Thanks for the bug report -- I think this may be related to bug #1
in the BUGS file.  I have added your description to it -- as yet we 
don't have a resolution for the problem.

--
best regards,

Brian Gough

Network Theory Ltd,
Publishing the GSL Manual - http://www.network-theory.co.uk/gsl/manual/