Re: gnuplot numerical errors on Intel MacBook

[<br...@ph...>]

CM wrote:

> No, that's not what I'm seeing.  I'm seeing a graph with dotted lines 
> but no function output.  I have posted one more picture, this time the 
> result of running
> 
> plot [1:2] gamma(x)
> 
> It's rather interesting, and I'm afraid not terribly enlightening.

Actually, it is.  It matches my original guess perfectly.  It shows
exactly what you would get if signgam is random garbage, which just so 
happens to equal -5.58e8.  This is because the implementation of the 
user-visible function gamma() is internally:

	double gamma(gamma x) {
             return exp(GAMMA(x)) * signgam;
         }

[see specfun.c:f_gamma()], where GAMMA is either lgamma(), gamma(), or 
gnuplot's own lngamma(), depending on availability.  The correct values 
of gamma(1) and gamma(2) are 1.0, yours are -5.58e08, but other than 
that, the shape is quite right.  I get exactly your plot, but for

      plot [1:2] -5.58e8*gamma(x)

Please check your config.log's lines about signgam.

The true test would be that while gamma() is wrong, lgamma() plots 
correctly.