NAG Library Manual, Mark 27.2
Interfaces:  FL   CL   CPP   AD 

NAG CL Interface Introduction
Example description
/* nag_smooth_fit_spline_parest (g10acc) 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, 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;
}