NAG Library Manual, Mark 28.7
Interfaces:  FL   CL   CPP   AD 

NAG CL Interface Introduction
Example description
/* nag_fit_dim2_cheb_eval (e02cbc) Example Program.
 *
 * Copyright 2022 Numerical Algorithms Group.
 *
 * Mark 28.7, 2022.
 */

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

int main(void) {
  /* Scalars */
  double x1, xm, xmax, xmin, y, ymax, ymin;
  Integer exit_status, i, j, k, l, m, n, ncoef, one;
  NagError fail;

  /* Arrays */
  double *a = 0, *ff = 0, *x = 0;

  INIT_FAIL(fail);

  exit_status = 0;
  printf("nag_fit_dim2_cheb_eval (e02cbc) Example Program Results\n");

  /* Skip heading in data file */
  scanf("%*[^\n] ");
  while (scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &k, &l) !=
         EOF)
  {
    /* Allocate array a */
    ncoef = (k + 1) * (l + 1);
    if (!(a = NAG_ALLOC(ncoef, double))) {
      printf("Allocation failure\n");
      exit_status = -1;
      goto END;
    }

    for (i = 0; i < ncoef; ++i)
      scanf("%lf", &a[i]);
    scanf("%*[^\n] ");
    scanf("%lf%lf%*[^\n] ", &ymin, &ymax);

    for (i = 0; i < n; ++i) {
      scanf("%lf%" NAG_IFMT "%lf%lf%lf%lf%*[^\n] ", &y, &m, &xmin, &xmax, &x1,
            &xm);

      /* Allocate arrays x and ff */
      if (!(x = NAG_ALLOC(m, double)) || !(ff = NAG_ALLOC(m, double))) {
        printf("Allocation failure\n");
        exit_status = -1;
        goto END;
      }

      for (j = 0; j < m; ++j)
        x[j] = x1 + (xm - x1) * (double)j / (double)(m - 1);

      one = 1;
      /* nag_fit_dim2_cheb_eval (e02cbc).
       * Evaluation of fitted polynomial in two variables
       */
      nag_fit_dim2_cheb_eval(one, m, k, l, x, xmin, xmax, y, ymin, ymax, ff, a,
                             &fail);
      if (fail.code != NE_NOERROR) {
        printf("Error from nag_fit_dim2_cheb_eval (e02cbc).\n%s\n",
               fail.message);
        exit_status = 1;
        goto END;
      }

      printf("\n");
      printf("y = %13.4e\n", y);
      printf("\n");
      printf("  i     x(i)      Poly(x(i),y)\n");
      for (j = 0; j < m; ++j)
        printf("%3" NAG_IFMT "%13.4e%13.4e\n", j, x[j], ff[j]);

      NAG_FREE(ff);
      NAG_FREE(x);
    }

    NAG_FREE(a);
  }

END:
  NAG_FREE(a);
  NAG_FREE(ff);
  NAG_FREE(x);

  return exit_status;
}