/* nag_zero_nonlin_eqns_1 (c05tbc) Example Program.
 *
 * Copyright 1998 Numerical Algorithms Group.
 *
 * Mark 5, 1998.
 * 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[], Integer *userflag,
                Nag_User *comm);
#ifdef __cplusplus
}
#endif

int main(void)
{

  Integer exit_status=0, i, j, n=9;
  NagError fail;
  Nag_User comm;
  double *fvec=0, *x=0, xtol;

  INIT_FAIL(fail);


  Vprintf("nag_zero_nonlin_eqns_1 (c05tbc) Example Program Results\n");
  if (n>0)
    {
      if ( !( 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;
    }

  /* The following starting values provide a rough solution. */
  for (j=0; j<n; j++)
    x[j] = -1.0;
  /* nag_machine_precision (x02ajc).
   * The machine precision
   */
  xtol = sqrt(X02AJC);
  /* nag_zero_nonlin_eqns_1 (c05tbc).
   * Solution of a system of nonlinear equations (function
   * values only), thread-safe
   */
  nag_zero_nonlin_eqns_1(n, x, fvec, f, xtol, &comm, &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_1 (c05tbc).\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 (i=0; i<n;  i++)
            Vprintf("%12.4f%s",x[i], (i%3==2 || i==n-1) ? "\n" : " " );
          exit_status = 2;
        }
    }
 END:
  if (fvec) NAG_FREE(fvec);
  if (x) NAG_FREE(x);
  return exit_status;
}
static void f(Integer n, double x[], double fvec[], Integer *userflag,
              Nag_User *comm)
{
  Integer k;

  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;
    }
}