NAG Library Manual, Mark 27.2
```/* nag_interp_dim2_scat_shep (e01sgc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

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

int main(void) {

/* Scalars */
Integer exit_status, i, m, n, nq, nw;
Integer liq, lrq;

/* Arrays */
double *f = 0, *q = 0, *qx = 0, *qy = 0, *rq = 0, *u = 0, *v = 0, *x = 0;
double *y = 0;
Integer *iq = 0;

/* Nag Types */
NagError fail;

exit_status = 0;
INIT_FAIL(fail);

printf("nag_interp_dim2_scat_shep (e01sgc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");

/* Input the number of nodes. */
scanf("%" NAG_IFMT "%*[^\n] ", &m);
if (m > 6) {
liq = 2 * m + 1;
lrq = 6 * m + 5;
/* Allocate memory */
if (!(f = NAG_ALLOC(m, double)) || !(rq = NAG_ALLOC(lrq, double)) ||
!(x = NAG_ALLOC(m, double)) || !(y = NAG_ALLOC(m, double)) ||
!(iq = NAG_ALLOC(liq, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
} else {
printf("Invalid m.\n");
exit_status = 1;
return exit_status;
}

/* Input the data points X,Y and F. */

for (i = 1; i <= m; ++i) {
scanf("%lf%lf%lf%*[^\n] ", &x[i - 1], &y[i - 1], &f[i - 1]);
}

/* Generate the interpolant. */
nq = 0;
nw = 0;
/* nag_interp_dim2_scat_shep (e01sgc).
* Interpolating functions, modified Shepard's method, two
* variables
*/
nag_interp_dim2_scat_shep(m, x, y, f, nw, nq, iq, rq, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_interp_dim2_scat_shep (e01sgc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Input the number of evaluation points. */
scanf("%" NAG_IFMT "%*[^\n] ", &n);
if (!(q = NAG_ALLOC(n, double)) || !(qx = NAG_ALLOC(n, double)) ||
!(qy = NAG_ALLOC(n, double)) || !(u = NAG_ALLOC(n, double)) ||
!(v = NAG_ALLOC(n, double))) {
printf("Allocation failure\n");
exit_status = 1;
goto END;
}

/* Input the evaluation points. */

for (i = 1; i <= n; ++i) {
scanf("%lf%lf%*[^\n] ", &u[i - 1], &v[i - 1]);
}

/* Evaluate the interpolant using nag_interp_dim2_scat_shep_eval (e01shc). */

/* nag_interp_dim2_scat_shep_eval (e01shc).
* Interpolated values, evaluate interpolant computed by
* nag_interp_dim2_scat_shep (e01sgc), function and first
* derivatives, two variables
*/
nag_interp_dim2_scat_shep_eval(m, x, y, f, iq, rq, n, u, v, q, qx, qy, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_interp_dim2_scat_shep (e01sgc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

printf("%s", "     I      U(I)      V(I)      Q(I)");
printf("\n");
for (i = 1; i <= n; ++i) {
printf("%6" NAG_IFMT "%10.2f%10.2f%10.2f\n", i, u[i - 1], v[i - 1],
q[i - 1]);
}

END:
NAG_FREE(f);
NAG_FREE(q);
NAG_FREE(qx);
NAG_FREE(qy);
NAG_FREE(rq);
NAG_FREE(u);
NAG_FREE(v);
NAG_FREE(x);
NAG_FREE(y);
NAG_FREE(iq);

return exit_status;
}
```