URL:
<https://savannah.gnu.org/bugs/?58065>
Summary: gsl_sf_gegenpoly_n returning unexpected values
Project: GNU Scientific Library
Submitted by: jacksonvanover
Submitted on: Sat 28 Mar 2020 05:25:33 PM UTC
Category: None
Severity: 3 - Normal
Operating System: Ubuntu 18.04
Status: None
Assigned to: None
Open/Closed: Open
Release: 2.6
Discussion Lock: Any
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Details:
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 the second argument is 0, mpmath and scipy's implementations of
the gegenbauer polynomial agree that the output should be uniformly 0,
but gsl_sf_gegenpoly_n consistently returns nonzero values. This
happens regardless of the value of the first argument, though in
particular when the first argument is 1 and the second is 0, the
function returns twice the third argument...
#include <gsl/gsl_sf.h>
#include <stdio.h>
#include <gsl/gsl_math.h>
#include <float.h>
int main (void){
double out;
out = gsl_sf_gegenpoly_n(1, 0, 5);
printf("%.*f\n", DBL_DIG-1, out);
printf("%.21e\n", out);
return 0;
}
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