7.33 Examples
The following example demonstrates the use of the error handling form of
the special functions, in this case to compute the Bessel function
J_0(5.0),
| | #include <stdio.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_sf_bessel.h>
int
main (void)
{
double x = 5.0;
gsl_sf_result result;
double expected = -0.17759677131433830434739701;
int status = gsl_sf_bessel_J0_e (x, &result);
printf ("status = %s\n", gsl_strerror(status));
printf ("J0(5.0) = %.18f\n"
" +/- % .18f\n",
result.val, result.err);
printf ("exact = %.18f\n", expected);
return status;
}
|
Here are the results of running the program,
| | $ ./a.out
status = success
J0(5.0) = -0.177596771314338292
+/- 0.000000000000000193
exact = -0.177596771314338292
|
The next program computes the same quantity using the natural form of
the function. In this case the error term result.err and return
status are not accessible.
| | #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;
}
|
The results of the function are the same,
| | $ ./a.out
J0(5.0) = -0.177596771314338292
exact = -0.177596771314338292
|
