#include <stdio.h>

#include <gsl/gsl_sf_bessel.h>

int

main (void)

{

  double x = 5.0;

  double expected = -0.17759677131433830434739701;

  double y = gsl_sf_bessel_J0 (x);

  printf ("J0(5.0) = %.18f\n", y);

  printf ("exact   = %.18f\n", expected);

  return 0;

}