```/* nag_1d_quad_inf_wt_trig_1 (d01ssc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*
*/

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <math.h>
#include <nagd01.h>
#include <nagx01.h>

#ifdef __cplusplus
extern "C"
{
#endif
static double NAG_CALL g(double x, Nag_User *comm);
#ifdef __cplusplus
}
#endif

int main(void)
{
static Integer use_comm[1] = { 1 };
Integer exit_status = 0;
double a;
double omega;
double epsabs, abserr;
Nag_TrigTransform wt_func;
double result;
Integer maxintervals, maxsubint_per_int;
NagError fail;
Nag_User comm;

INIT_FAIL(fail);

printf("nag_1d_quad_inf_wt_trig_1 (d01ssc) Example Program Results\n");

/* For communication with user-supplied functions: */
comm.p = (Pointer) &use_comm;

epsabs = 0.001;
a = 0.0;
/* nag_pi (x01aac).
* pi
*/
omega = nag_pi * 0.5;
wt_func = Nag_Cosine;
maxintervals = 50;
maxsubint_per_int = 500;

* interval, sine or cosine weight function, thread-safe
*/
nag_1d_quad_inf_wt_trig_1(g, a, omega, wt_func, maxintervals,
maxsubint_per_int, epsabs, &result, &abserr,
&qpsub, &comm, &fail);
printf("a      - lower limit of integration = %10.4f\n", a);
printf("b      - upper limit of integration = infinity\n");
printf("epsabs - absolute accuracy requested = %11.2e\n\n", epsabs);
if (fail.code != NE_NOERROR)
printf("Error from nag_1d_quad_inf_wt_trig_1 (d01ssc) %s\n",
fail.message);
if (fail.code != NE_INT_ARG_LT && fail.code != NE_BAD_PARAM &&
fail.code != NE_ALLOC_FAIL && fail.code != NE_NO_LICENCE) {
printf("result - approximation to the integral = %9.5f\n", result);
printf("abserr - estimate of the absolute error = %11.2e\n", abserr);
printf("qpsub.fun_count  - number of function evaluations ="
" %4" NAG_IFMT "\n", qpsub.fun_count);
printf("qpsub.intervals  - number of intervals used = %4" NAG_IFMT "\n",
qpsub.intervals);
printf("qpsub.subints_per_interval  - \n"
"maximum number of subintervals used in any one interval ="
" %4" NAG_IFMT "\n", qpsub.subints_per_interval);
/* Free memory used by qpsub */
NAG_FREE(qpsub.interval_error);
NAG_FREE(qpsub.interval_result);
NAG_FREE(qpsub.interval_flag);
}
else {
exit_status = 1;
goto END;
}

END:
return exit_status;
}

static double NAG_CALL g(double x, Nag_User *comm)
{
Integer *use_comm = (Integer *) comm->p;

if (use_comm[0]) {
printf("(User-supplied callback g, first invocation.)\n");
use_comm[0] = 0;
}

return (x > 0.0) ? 1.0 / sqrt(x) : 0.0;
}
```