Re: [Fwd: Re: gnuplot numerical errors on Intel MacBook]

[Ethan M. <merritt@u.washington.edu>]

On Thursday 28 September 2006 02:30 pm, Daniel J Sebald wrote:
>
> I'm not so certain we have shown that it is broken.  My point is that
> signgam has no relation to lgamma() anymore in the context of C99. 

You are spouting nonsense. 

ISO/IEC C99 (including Annex F, "IEC 60559 floating-point arithmetic")
and
POSIX 2001 (IEEE Std 1003.1:2001) 

require lgamma() to provide signgam as an extern int


I quote from the document 
"Rationale for International Standard  Programming Languages  
 C Revision 5.10 April-2003"

7.12.8.3 The lgamma functions 
New feature for C99. Since the mathematical gamma function increases in 
value so quickly (it is around 10306 for an argument of only 170), the 
logarithm of gamma extends the useful domain. Also, for computing 
combinations and permutations, it is the quotient of the (potentially 
large) gammas that is needed; taking differences of the lgammas instead 
allows for calculations without overflow. In Single Unix, a call to 
lgamma sets an external variable, signgam, to the sign of gamma(x), 
which is  1 if x < 0 && remainder(floor(x), 2) != 0. Note that this 
specification does not remove the external identifier signgam from the 
user's name space. An implementation that supports lgamma's setting of 
signgam as an extension must still protect the external identifier 
signgam if defined by the user.

-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle WA