Limit for gsl_sf_Si

[Jackson Vanover]

Using version 2.6 of GSL from ftp://ftp.gnu.org/gnu/gsl/gsl-2.6.tar.gz

OS is Ubuntu 18.04.2 LTS

Hardware is a Dell workstation with a 3.60 GHz Intel i7-4790 and 32 GB
of RAM

Compiler is gcc 7.4.0 with the -w option

When evaluating the Si(inf), we get a return of NaN though the limit
approaches 1.570796326794896619231322 (
http://mpmath.org/doc/1.1.0/functions/expintegrals.html?highlight=si#mpmath.si
)

#include <gsl/gsl_sf.h>
#include <stdio.h>
#include <gsl/gsl_math.h>

int main (void){
double out;
out = gsl_sf_Si(GSL_POSINF);

printf("%f\n", out);
printf("%.21e\n", out);
return 0;
}

Best,
Jackson Vanover