/* nag_quad_md_gauss (d01fbc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.3, 2024.
*/
#include <math.h>
#include <nag.h>
#include <stdio.h>
#ifdef __cplusplus
extern "C" {
#endif
static double NAG_CALL fun(Integer ndim, const double x[], Nag_Comm *comm);
#ifdef __cplusplus
}
#endif
int main(void) {
static double ruser[1] = {-1.0};
Integer exit_status = 0;
Integer ndim;
double a, ans, b;
Integer i, j, lwa;
double *abscis = 0, *weight = 0;
Integer *nptvec = 0;
char nag_enum_arg[40];
Nag_Comm comm;
Nag_QuadType quadtype;
NagError fail;
INIT_FAIL(fail);
printf("nag_quad_md_gauss (d01fbc) Example Program Results\n");
/* For communication with user-supplied functions: */
comm.user = ruser;
/* Skip heading in data file */
scanf("%*[^\n] ");
/* Input parameters */
scanf("%" NAG_IFMT "%*[^\n] ", &ndim);
if (!(nptvec = NAG_ALLOC(ndim, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
lwa = 0.0;
for (i = 0; i < ndim; i++) {
scanf("%" NAG_IFMT " ", &nptvec[i]);
lwa = lwa + nptvec[i];
}
scanf("%*[^\n] ");
if (!(abscis = NAG_ALLOC(lwa, double)) ||
!(weight = NAG_ALLOC(lwa, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
j = 0;
for (i = 0; i < ndim; i++) {
/* Nag_QuadType */
scanf("%39s%*[^\n] ", nag_enum_arg);
quadtype = (Nag_QuadType)nag_enum_name_to_value(nag_enum_arg);
scanf("%lf %lf%*[^\n] ", &a, &b);
/* nag_quad_dim1_gauss_wres (d01tbc).
* Pre-computed weights and abscissae for
* Gaussian quadrature rules, restricted choice of rule.
*/
nag_quad_dim1_gauss_wres(quadtype, a, b, nptvec[i], &weight[j], &abscis[j],
&fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_quad_dim1_gauss_wres (d01tbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
j = j + nptvec[i];
}
/* nag_quad_md_gauss (d01fbc).
* Multidimensional Gaussian quadrature over hyper-rectangle.
*/
ans = nag_quad_md_gauss(ndim, nptvec, lwa, weight, abscis, fun, &comm, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_quad_md_gauss (d01fbc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("\nAnswer = %10.5f\n", ans);
END:
NAG_FREE(nptvec);
NAG_FREE(abscis);
NAG_FREE(weight);
return exit_status;
}
static double NAG_CALL fun(Integer ndim, const double x[], Nag_Comm *comm) {
if (comm->user[0] == -1.0) {
printf("(User-supplied callback fun, first invocation.)\n");
comm->user[0] = 0.0;
}
return pow((x[0] * x[1] * x[2]), 6) / pow((x[3] + 2.0), 8) *
exp(-2.0 * x[1] - 0.5 * x[2] * x[2]);
}