```/* nag_1d_quad_brkpts_1 (d01slc) 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>

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

int main(void)
{
static Integer use_comm[1] = {1};
Integer          exit_status = 0;
double           a, b;
double           epsabs, abserr, epsrel, brkpts[1], result;
Integer          nbrkpts;
Nag_QuadProgress qp;
Integer          max_num_subint;
NagError         fail;
Nag_User         comm;

INIT_FAIL(fail);

printf("nag_1d_quad_brkpts_1 (d01slc) Example Program Results\n");

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

nbrkpts = 1;
epsabs = 0.0;
epsrel = 0.001;
a = 0.0;
b = 1.0;
max_num_subint = 200;
brkpts[0] = 1.0/7.0;
/* nag_1d_quad_brkpts_1 (d01slc).
* One-dimensional adaptive quadrature, allowing for
* singularities at specified points, thread-safe
*/
nag_1d_quad_brkpts_1(f, a, b, nbrkpts, brkpts, epsabs, epsrel,
max_num_subint,
&result, &abserr, &qp, &comm,
&fail);
printf("a      - lower limit of integration = %10.4f\n", a);
printf("b      - upper limit of integration = %10.4f\n", b);
printf("epsabs - absolute accuracy requested = %11.2e\n", epsabs);
printf("epsrel - relative accuracy requested = %11.2e\n\n", epsrel);
printf("brkpts[0] - given break-point = %10.4f\n", brkpts[0]);
if (fail.code != NE_NOERROR)
printf("Error from nag_1d_quad_brkpts_1 (d01slc) %s\n",
fail.message);
if (fail.code != NE_INT_ARG_LT && fail.code != NE_2_INT_ARG_LE &&
fail.code != NE_ALLOC_FAIL && fail.code != NE_NO_LICENCE)
{
/* Free memory used by qp */
NAG_FREE(qp.sub_int_beg_pts);
NAG_FREE(qp.sub_int_end_pts);
NAG_FREE(qp.sub_int_result);
NAG_FREE(qp.sub_int_error);
}
if (fail.code != NE_INT_ARG_LT && fail.code != NE_2_INT_ARG_LE
&& fail.code != NE_QUAD_BRKPTS_INVAL && 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("qp.fun_count  - number of function evaluations = %4ld\n",
qp.fun_count);
printf("qp.num_subint  - number of subintervals used = %4ld\n",
qp.num_subint);
}
else
{
exit_status = 1;
goto END;
}

END:
return exit_status;
}

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

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

a = FABS(x-1.0/7.0);
return (a != 0.0)?pow(a, -0.5):0.0;
}
```