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Re: [Help-gsl] ln gamma |x| too large error

From: Brian Gough
Subject: Re: [Help-gsl] ln gamma |x| too large error
Date: Tue, 20 Mar 2007 12:35:47 +0000
User-agent: Wanderlust/2.14.0 (Africa) Emacs/21.3 Mule/5.0 (SAKAKI)

At Fri, 16 Mar 2007 10:38:48 +0000 (GMT),
Clare Quarman wrote:
> When using the special function lngamma_sgn_e, sometimes I receive an
> error, the only info is that it's from line 1249 in gamma.c.  Looking at
> this bit of gamma.c, a nearby comment states that |x| is too large for the 
> fractional part to be extracted.
> I'm wondering if this restriction the same both for +ve and -ve values of
> x, and what constitutes too large a magnitude for x?
> Does anyone understand what's going on here?

The gamma function has a singularity at every negative integer, and
for x < -1e15 there isn't enough precision to distinguish between
integer and non-integer values in double-precision -- that is when
this error should occur.

Brian Gough

Network Theory Ltd,
Publishing Free Software Manuals ---

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