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gsl_sf_gegenpoly_n returning unexpected values
From: |
Jackson Vanover |
Subject: |
gsl_sf_gegenpoly_n returning unexpected values |
Date: |
Wed, 4 Mar 2020 09:49:20 -0800 |
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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