/* nag_zero_nonlin_eqns_deriv (c05pbc) 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 <math.h>
#include <nagc05.h>
#include <nagx02.h>

#ifdef __cplusplus
extern "C" {
#endif
  static void f(Integer n, double x[], double fvec[], double fjac[],
                Integer tdfjac, Integer *userflag);
#ifdef __cplusplus
}
#endif

int main(void)
{

  Integer exit_status=0, j, n=9, tdfjac;
  NagError fail;
  double *fjac=0, *fvec=0, *x=0, xtol;

  INIT_FAIL(fail);
  Vprintf("nag_zero_nonlin_eqns_deriv (c05pbc) Example Program Results\n");
  /* The following starting values provide a rough solution. */
  if (n>0)
    {

      if ( !( fjac = NAG_ALLOC(n*n, double)) ||
           !( fvec = NAG_ALLOC(n, double)) ||
           !( x = NAG_ALLOC(n, double)) )
        {
          Vprintf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  else
    {
      Vprintf("Invalid n.\n");
      exit_status = 1;
      return exit_status;
    }

  for (j=0; j<n; j++)
    x[j] = -1.0;
  tdfjac = n;
  /* nag_machine_precision (x02ajc).
   * The machine precision
   */
  xtol = sqrt(X02AJC);
  /* nag_zero_nonlin_eqns_deriv (c05pbc).
   * Solution of a system of nonlinear equations (using first
   * derivatives)
   */
  nag_zero_nonlin_eqns_deriv(n, x, fvec, fjac, tdfjac, f, xtol, &fail);
  if (fail.code == NE_NOERROR)
    {
      Vprintf("Final approximate solution\n\n");
      for (j=0; j<n; j++)
        Vprintf("%12.4f%s",x[j], (j%3==2 || j==n-1) ? "\n" : " " );
    }
  else
    {
      Vprintf("Error from nag_zero_nonlin_eqns_deriv (c05pbc).\n%s\n",
              fail.message);
      if (fail.code == NE_TOO_MANY_FUNC_EVAL ||
          fail.code == NE_XTOL_TOO_SMALL ||
          fail.code ==  NE_NO_IMPROVEMENT)
        {
          Vprintf("Approximate solution\n\n");
          for (j=0; j<n; j++)
            Vprintf("%12.4f%s",x[j], (j%3==2 || j==n-1) ? "\n" : " " );
        }
      exit_status = 1;
    }
 END:
  if (fjac) NAG_FREE(fjac);
  if (fvec) NAG_FREE(fvec);
  if (x) NAG_FREE(x);
  return exit_status;
}
static void f(Integer n, double x[], double fvec[], double fjac[],
              Integer tdfjac, Integer *userflag)
{
#define FJAC(I,J) fjac[((I))*tdfjac+(J)]
  Integer j, k;

  if (*userflag != 2)
    {
      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
    {
      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;
        }
    }
}