```/* nag_1d_quad_inf_wt_trig_1 (d01ssc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 5, 1998.
* Mark 6 revised, 2000.
* Mark 7 revised, 2001.
*
*/

#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(

/* 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
*/
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)
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 ="
" %4ld\n", qpsub.fun_count);
printf("qpsub.intervals  - number of intervals used = %4ld\n",
qpsub.intervals);
printf("qpsub.subints_per_interval  - \n"
"maximum number of subintervals used in any one interval ="
" %4ld\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;
}
```