/* nag_rand_quasi_uniform (g05ymc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.1, 2024.
*/
/* Pre-processor includes */
#include <math.h>
#include <nag.h>
#include <stdio.h>
#define QUAS(I, J) \
quas[(order == Nag_ColMajor) ? (J * pdquas + I) : (I * pdquas + J)]
int main(void) {
/* Integer scalar and array declarations */
Integer exit_status = 0;
Integer liref, d, i, j, q_size;
Integer *iref = 0;
Integer pdquas;
/* NAG structures */
NagError fail;
/* Double scalar and array declarations */
double sum, tmp, vsbl;
double *quas = 0;
/* Number of dimensions */
Integer idim = 8;
/* Set the sample size */
Integer n = 200;
/* Skip the first 1000 variates */
Integer iskip = 1000;
/* Use row major order */
Nag_OrderType order = Nag_RowMajor;
/* Choose the quasi generator */
Nag_QuasiRandom_Sequence genid = Nag_QuasiRandom_Sobol;
/* Initialize the error structure */
INIT_FAIL(fail);
printf("nag_rand_quasi_uniform (g05ymc) Example Program Results\n");
pdquas = (order == Nag_RowMajor) ? idim : n;
q_size = (order == Nag_RowMajor) ? pdquas * n : pdquas * idim;
/* Calculate the size of the reference vector */
liref = (genid == Nag_QuasiRandom_Faure) ? 407 : 32 * idim + 7;
/* Allocate arrays */
if (!(quas = NAG_ALLOC(q_size, double)) ||
!(iref = NAG_ALLOC(liref, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Initialize the Sobol generator */
nag_rand_quasi_init(genid, idim, iref, liref, iskip, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_rand_quasi_init (g05ylc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Generate n quasi-random variates */
nag_rand_quasi_uniform(order, n, quas, pdquas, iref, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_rand_quasi_uniform (g05ymc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Estimate integral by evaluating function at each variate and summing */
sum = 0.0e0;
for (i = 0; i < n; i++) {
tmp = 1.0e0;
for (d = 0; d < idim; d++)
tmp *= fabs(4.0e0 * QUAS(i, d) - 2.0e0);
sum += tmp;
}
/* Convert sum to mean value */
vsbl = sum / (double)n;
/* Print the estimated value of the integral */
printf("Value of integral = %8.4f\n\n", vsbl);
/* Display the first 10 variates used */
printf("First 10 variates\n");
for (i = 0; i < 10; i++) {
printf(" %3" NAG_IFMT " ", i + 1);
for (j = 0; j < idim; j++)
printf("%8.4f%s", QUAS(i, j), ((j + 1) % 20) ? " " : "\n");
if (idim % 20)
printf("\n");
}
END:
NAG_FREE(quas);
NAG_FREE(iref);
return exit_status;
}