/* nag_1d_spline_interpolant (e01bac) Example Program.
 *
 * Copyright 1991 Numerical Algorithms Group.
 *
 * Mark 2, 1991.
 *
 * Mark 6 revised, 2000.
 * Mark 8 revised, 2004.
 */

#include <nag.h>
#include <stdio.h>
#include <math.h>
#include <nag_stdlib.h>
#include <nage01.h>
#include <nage02.h>

#define MMAX 7

int main(void)
{
  Integer    exit_status = 0, i, j, m = MMAX;
  NagError   fail;
  Nag_Spline spline;
  double     fit, *x = 0, xarg, *y = 0;

  INIT_FAIL(fail);

  /* Initialise spline */
  spline.lamda = 0;
  spline.c = 0;

  printf(
          "nag_1d_spline_interpolant (e01bac) Example Program Results\n");

  if (m >= 1)
    {
      if (!(y = NAG_ALLOC(m, double)) ||
          !(x = NAG_ALLOC(m, double)))
        {
          printf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  else
    {
      exit_status = 1;
      return exit_status;
    }

  x[0] = 0.0; x[1] = 0.2; x[2] = 0.4;
  x[3] = 0.6; x[4] = 0.75; x[5] = 0.9; x[6] = 1.0;

  for (i = 0; i < m; ++i)
    y[i] = exp(x[i]);
  /* nag_1d_spline_interpolant (e01bac).
   * Interpolating function, cubic spline interpolant, one
   * variable
   */
  nag_1d_spline_interpolant(m, x, y, &spline, &fail);
  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_1d_spline_interpolant (e01bac).\n%s\n",
              fail.message);
      exit_status = 1;
      goto END;
    }

  printf("\nNumber of distinct knots = %ld\n\n", m-2);
  printf("Distinct knots located at \n\n");
  for (j = 3; j < m+1; j++)
    printf("%8.4f%s", spline.lamda[j], (j-3)%5 == 4 || j == m?"\n":" ");
  printf("\n\n    J    B-spline coeff c\n\n");
  for (j = 0;  j < m; ++j)
    printf("    %ld  %13.4f\n", j+1, spline.c[j]);
  printf(
          "\n    J       Abscissa            Ordinate            Spline\n\n");
  for (j = 0; j < m; ++j)
    {
      /* nag_1d_spline_evaluate (e02bbc).
       * Evaluation of fitted cubic spline, function only
       */
      nag_1d_spline_evaluate(x[j], &fit, &spline, &fail);
      if (fail.code != NE_NOERROR)
        {
          printf("Error from nag_1d_spline_evaluate (e02bbc).\n%s\n",
                  fail.message);
          exit_status = 1;
          goto END;
        }

      printf("    %ld %13.4f      %13.4f       %13.4f\n",
              j+1, x[j], y[j], fit);
      if (j < m-1)
        {
          xarg = (x[j] + x[j+1]) * 0.5;
          /* nag_1d_spline_evaluate (e02bbc), see above. */
          nag_1d_spline_evaluate(xarg, &fit, &spline, &fail);
          if (fail.code != NE_NOERROR)
            {
              printf(
                      "Error from nag_1d_spline_evaluate (e02bbc).\n%s\n",
                      fail.message);
              exit_status = 1;
              goto END;
            }
          printf("      %13.4f                          %13.4f\n",
                  xarg, fit);
        }
    }
  /* Free memory allocated by nag_1d_spline_interpolant (e01bac) */
 END:
  if (y) NAG_FREE(y);
  if (x) NAG_FREE(x);
  NAG_FREE(spline.lamda);
  NAG_FREE(spline.c);
  return exit_status;
}