NAG Library Manual, Mark 27.2
```/* nag_fit_dim2_spline_evalv (e02dec) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

#include <nag.h>
#include <stdio.h>

int main(void) {
Integer exit_status = 0, i, m;
NagError fail;
Nag_2dSpline spline;
double *ff = 0, *x = 0, *y = 0;

INIT_FAIL(fail);

/* Initialize spline */
spline.lamda = 0;
spline.mu = 0;
spline.c = 0;

printf("nag_fit_dim2_spline_evalv (e02dec) Example Program Results\n");
scanf("%*[^\n]"); /* Skip heading in data file */
/* Read m, the number of spline evaluation points. */
scanf("%" NAG_IFMT "", &m);
if (m >= 1) {
if (!(x = NAG_ALLOC(m, double)) || !(y = NAG_ALLOC(m, double)) ||
!(ff = NAG_ALLOC(m, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
} else {
printf("Invalid m.\n");
exit_status = 1;
return exit_status;
}
/* Read nx and ny, the number of knots in the x and y directions. */
scanf("%" NAG_IFMT "%" NAG_IFMT "", &(spline.nx), &(spline.ny));
if (spline.nx >= 8 && spline.ny >= 8) {
if (!(spline.c = NAG_ALLOC((spline.nx - 4) * (spline.ny - 4), double)) ||
!(spline.lamda = NAG_ALLOC(spline.nx, double)) ||
!(spline.mu = NAG_ALLOC(spline.ny, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
} else {
printf("Invalid spline.nx or spline.ny.\n");
exit_status = 1;
return exit_status;
}

/* read the knots lamda .. lamda[nx-1] and mu .. mu[ny-1]. */
for (i = 0; i < spline.nx; i++)
scanf("%lf", &(spline.lamda[i]));
for (i = 0; i < spline.ny; i++)
scanf("%lf", &(spline.mu[i]));
/* Read c, the bicubic spline coefficients. */
for (i = 0; i < (spline.nx - 4) * (spline.ny - 4);
scanf("%lf", &(spline.c[i])), i++)
;
/* Read the x and y co-ordinates of the evaluation points. */
for (i = 0; i < m; i++)
scanf("%lf%lf", &x[i], &y[i]);
/* Evaluate the spline at the m points. */
/* nag_fit_dim2_spline_evalv (e02dec).
* Evaluation of bicubic spline, at a set of points
*/
nag_fit_dim2_spline_evalv(m, x, y, ff, &spline, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fit_dim2_spline_evalv (e02dec).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print the results. */
printf("      i          x[i]       y[i]       ff[i]\n");
for (i = 0; i < m; i++)
printf("%7" NAG_IFMT "    %11.3f%11.3f%11.3f\n", i, x[i], y[i], ff[i]);
NAG_FREE(spline.lamda);
NAG_FREE(spline.mu);
NAG_FREE(spline.c);
END:
NAG_FREE(x);
NAG_FREE(y);
NAG_FREE(ff);
return exit_status;
}
```