/* nag_quad_dim1_inf_exp_wt (d01ubc) Example Program.
 *
 * Copyright 2021 Numerical Algorithms Group.
 *
 * Mark 27.3, 2021.
 */
#include <math.h>
#include <nag.h>

#ifdef __cplusplus
extern "C" {
#endif
static void NAG_CALL fun(const double x[], double f[], const Integer n,
                         Nag_Comm *comm, Integer *istop);
#ifdef __cplusplus
}
#endif

int main(void) {
  static double ruser[2] = {-1.0, -1.0};
  /* Scalars */
  Integer exit_status = 0;
  double ans;
  Integer n;
  /* Nag Types */
  Nag_Comm comm;
  NagError fail;

  printf("nag_quad_dim1_inf_exp_wt (d01ubc) Example Program Results\n\n");

  /* For communication with user-supplied functions: */
  comm.user = ruser;

  INIT_FAIL(fail);

  n = 10;

  /* Compute the one-dimensional integral, from zero to infinity,
   * of a function weighted by exp(-x*x), using
   * nag_quad_dim1_inf_exp_wt (d01ubc).
   */
  nag_quad_dim1_inf_exp_wt(fun, n, &ans, &comm, &fail);
  switch (fail.code) {
  case NE_NOERROR: {
    /* The definite integral has been estimated. */
    printf("Number of abscissae used  = %5" NAG_IFMT "\n", n);
    printf("approximation to integral = %10.5f\n", ans);
    break;
  }
  case NE_USER_STOP: {
    /* A requested exit was made in fun. */
    printf("A stop was requested in fun by setting istop < 0\n\n");
    printf("%s\n", fail.message);
    exit_status++;
    break;
  }
  default: {
    /* A solution could not be calculated due to an illegal parameter
     * or other failure.
     */
    printf("%s\n", fail.message);
    exit_status++;
  }
  }
  return exit_status;
}

static void NAG_CALL fun(const double x[], double f[], const Integer n,
                         Nag_Comm *comm, Integer *istop) {
  Integer i;

  if (comm->user[0] == -1.0) {
    printf("(User-supplied callback fun, first invocation.)\n");
    comm->user[0] = 0.0;
  }
  for (i = 0; i < n; i++) {
    f[i] = x[i];
  }
  *istop = 0;
}