NAG Library Manual, Mark 30.1
Interfaces:  FL   CL   CPP   AD
```/* nag_smooth_fit_spline_parest (g10acc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.1, 2024.
*/

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

int main(void) {
Integer exit_status = 0, i, maxcal, n, nord;
Nag_SmoothParamMethods method;
Nag_Boolean weight;
char nag_enum_arg[40];
double crit, df, rho, rss, tol, u;
double *coeff = 0, *h = 0, *res = 0, *weights = 0, *wtptr;
double *wwt = 0, *x = 0, *xord = 0, *y = 0, *yhat = 0;
double *yord = 0;
NagError fail;

INIT_FAIL(fail);

printf("nag_smooth_fit_spline_parest (g10acc) Example Program Results\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "", &n);
if (!(x = NAG_ALLOC(n, double)) || !(y = NAG_ALLOC(n, double)) ||
!(weights = NAG_ALLOC(n, double)) || !(yhat = NAG_ALLOC(n, double)) ||
!(coeff = NAG_ALLOC((n - 1) * 3, double)) ||
!(res = NAG_ALLOC(n, double)) || !(h = NAG_ALLOC(n, double)) ||
!(wwt = NAG_ALLOC(n, double)) || !(yord = NAG_ALLOC(n, double)) ||
!(xord = NAG_ALLOC(n, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
scanf("%39s", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
method = (Nag_SmoothParamMethods)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s", nag_enum_arg);
weight = (Nag_Boolean)nag_enum_name_to_value(nag_enum_arg);

if (!weight) {
for (i = 1; i <= n; ++i)
scanf("%lf %lf", &x[i - 1], &y[i - 1]);
wtptr = 0;
} else {
for (i = 1; i <= n; ++i)
scanf("%lf %lf %lf", &x[i - 1], &y[i - 1], &weights[i - 1]);
wtptr = weights;
}
scanf("%lf %lf %" NAG_IFMT " %lf", &u, &tol, &maxcal, &crit);
/* Sort data, removing ties and weighting accordingly */
/* nag_smooth_data_order (g10zac).
* Reorder data to give ordered distinct observations
*/
nag_smooth_data_order(n, x, y, wtptr, &nord, xord, yord, wwt, &rss, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_smooth_data_order (g10zac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Fit cubic spline */
/* nag_smooth_fit_spline_parest (g10acc).
* Fit cubic smoothing spline, smoothing parameter estimated
*/
nag_smooth_fit_spline_parest(method, nord, xord, yord, wwt, yhat, coeff, &rss,
&df, res, h, &crit, &rho, u, tol, maxcal, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_smooth_fit_spline_parest (g10acc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print results */
printf("\n");
printf("%s%10.2f\n", " Residual sum of squares = ", rss);
printf("%s%10.2f\n", " Degrees of freedom = ", df);
printf("%s%10.2f\n", " rho = ", rho);
printf("\n");
printf("\n%s%s%s\n%s%s%s\n", "     Input data", "                ",
"Output results", "   i    x        y   ", "          ", "yhat     h");

for (i = 1; i <= nord; ++i)
printf("%4" NAG_IFMT " %8.3f %8.3f      %8.3f %8.3f\n", i, xord[i - 1],
yord[i - 1], yhat[i - 1], h[i - 1]);

END:
NAG_FREE(x);
NAG_FREE(y);
NAG_FREE(weights);
NAG_FREE(yhat);
NAG_FREE(coeff);
NAG_FREE(res);
NAG_FREE(h);
NAG_FREE(wwt);
NAG_FREE(yord);
NAG_FREE(xord);

return exit_status;
}
```