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Re: [Bug-gsl] Re: hyperg_U(a, b, x) Questions about x<0 and values of a

From: Brian Gough
Subject: Re: [Bug-gsl] Re: hyperg_U(a, b, x) Questions about x<0 and values of a,
Date: Wed, 21 Jul 2010 21:24:01 +0100
User-agent: Wanderlust/2.15.6 (Almost Unreal) Emacs/23.2 Mule/6.0 (HANACHIRUSATO)

At Sun, 11 Jul 2010 14:43:43 -0500,
Raymond Rogers wrote:
> hyperg_U basically fails with b=1, a non-integer; because
> gsl_sf_poch_e(1+a-b,-a,&r1); is throwing a domain error when given
> gamma(0)/gamma(a).
> Checking on and using b=1 after a-integer is checked is illustrated
> below in Octave.   I also put in recursion to evaluate b>=2.
> I checked the b=1 expression against Maple; for a few values x<0,a<0,b=1
> and x<0,a<0,b>=2 integer.
> --------------
> Unfortunately the routine in Octave to call hyperg_U  is only set up for
> real returns, which was okay for versions <1.14 .  Sad to say I am the
> one who implemented the hyperg_U interface, and will probably have to go
> back :-( .  Integrating these functions into Octave was not pleasant;
> but perhaps somebody made it easier.  I did translate the active parts
> of hyperg_U into octave though; so it can be used in that way.

Thanks for the comments, I've logged them for future review in the bug tracker 
It's a complicated function so it's going to take some time to digest it.

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