/* nag_check_deriv (c05zbc) Example Program.
 *
 * Copyright 1991 Numerical Algorithms Group.
 *
 * Mark 2, 1991.
 * Mark 7 revised, 2001.
 * Mark 8 revised, 2004.
 */

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nagc05.h>

#ifdef __cplusplus
extern "C" {
#endif
static void NAG_CALL f(Integer n, const double xc[], double fvecc[],
                       double fjacc[], Integer tdj, Integer *userflag);
#ifdef __cplusplus
}
#endif

int main(void)
{

#define FJAC(I, J) fjac[(I) *tdfjac + J]
  Integer  exit_status = 0, i, j, n, tdfjac;
  NagError fail;
  double   *fjac = 0, *fvec = 0, *x = 0;

  INIT_FAIL(fail);

  printf("nag_check_deriv (c05zbc) Example Program Results\n");
  n = 3;
  if (n > 0)
    {
      if (!(fjac = NAG_ALLOC(n*n, double)) ||
          !(fvec = NAG_ALLOC(n, double)) ||
          !(x = NAG_ALLOC(n, double)))
        {
          printf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }

      tdfjac = n;
    }
  else
    {
      printf("Invalid n.\n");
      exit_status = 1;
      return exit_status;
    }

  /* Set up an arbitrary point at which to check the 1st derivatives */
  x[0] = 9.2e-01;
  x[1] = 1.3e-01;
  x[2] = 5.4e-01;
  printf("The test point is ");
  for (j = 0; j < n; ++j)
    printf("%13.3e", x[j]);
  printf("\n\n");
  /* nag_check_deriv (c05zbc).
   * Derivative checker for nag_zero_nonlin_eqns_deriv
   * (c05pbc)
   */
  nag_check_deriv(n, x, fvec, fjac, tdfjac, f, &fail);
  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_check_deriv (c05zbc).\n%s\n",
              fail.message);
      exit_status = 1;
      goto END;
    }
  printf("1st derivatives are consistent with residual values.\n\n");
  printf("At the test point, f() gives\n\n");
  printf("    Residuals            1st derivatives\n\n");
  for (i = 0; i < n; ++i)
    {
      printf("%13.3e", fvec[i]);
      for (j = 0; j < n; ++j)
        printf("%13.3e", FJAC(i, j));
      printf("\n");
    }
 END:
  if (fjac) NAG_FREE(fjac);
  if (fvec) NAG_FREE(fvec);
  if (x) NAG_FREE(x);
  return exit_status;
}

static void NAG_CALL f(Integer n, const double x[], double fvec[],
		       double fjac[], Integer tdfjac, Integer *userflag)
{
  Integer j, k;

  if (*userflag != 2)
    {
      /* Calculate the function values */
      for (k = 0; k < n; k++)
        {
          fvec[k] = (3.0-x[k]*2.0) * x[k] + 1.0;
          if (k > 0) fvec[k] -= x[k-1];
          if (k < n-1) fvec[k] -= x[k+1] * 2.0;
        }
    }
  else
    {
      /* Calculate the corresponding first derivatives */
      for (k = 0; k < n; k++)
        {
          for (j = 0; j < n; j++)
            FJAC(k, j) = 0.0;
          FJAC(k, k) = 3.0 - x[k] * 4.0;
          if (k > 0)
            FJAC(k, k-1) = -1.0;
          if (k < n-1)
            FJAC(k, k+1) = -2.0;
        }
    }
}