bugGNU Scientific Library - Bugs: bug #57978, Incorrect result from cosine...


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bug #57978: Incorrect result from cosine function with inf input

Submitter:  Jackson Vanover <jacksonvanover>
Submitted:  Mon 09 Mar 2020 08:48:52 PM UTC
Category:  Accuracy problem Severity:  3 - Normal
Operating System:  Ubuntu 18.04 Status:  None
Assigned to:  None Open/Closed:  Open
Release:  2.6

Sat 28 Mar 2020 05:05:00 PM UTC, comment #1: 

Behavior also observed in gsl_sf_sin_pi

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

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

        printf("%f\n", out); // prints zero
        return 0;

Jackson Vanover <jacksonvanover>
Mon 09 Mar 2020 08:48:52 PM UTC, original submission:  

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

Description: when passing positive infinity to gsl_sf_cos_pi, the
result is 1 which doesn't make sense as the cosine function oscillates
between -1 and 1

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

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

printf("%f\n", out);
return 0;

Jackson Vanover <jacksonvanover>


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