Brian Gough <[email protected]>
Subject: Re: [Bug-gsl] hyperg_U(a,b,x) Questions about x<0 and values
of a
To: [email protected]
Cc: [email protected]
Message-ID: <43wrt61fkt.wl%[email protected]>
Content-Type: text/plain; charset=US-ASCII
At Wed, 07 Jul 2010 10:14:34 -0500,
Raymond Rogers wrote:
> >
> > 1) I was unable to find the valid domain of the argument a when x<0.
> > Experimenting yields what seem to be erratic results. Apparently
> > correct answers occur when {x<0&a<0& a integer}. References would be
> > sufficient. Unfortunately {x<0,a<0} is exactly the wrong range for my
> > problem; but the recursion relations can be used to stretch to a>0. If
> > I can find a range of correct operation for the domain of "a" of width >1.
>
| Brian Gough
| Thanks for the email. There are some comments about the domain for
| the hyperg_U_negx function in specfunc/hyperg_U.c -- do they help?
They explain some things, but I believe the section
if (b_int && b >= 2 && !(a_int && a <= (b - 2))){}
else {}
is implemented incorrectly; and probably the preceding section as well. Some
restructuring of the code would make things clearer; but things like that
should probably done in a different forum: email, blog, etc...
I think the switches might be wrong. In any case it seems that b=1 has a hole.
Is there a source for this code?
Note: the new NIST Mathematical handbook might have better algorithms. I am
certainly no expert on implementing mathematical functions (except for finding
ways to make them fail).
Ray
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