/* 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 <nagx04.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <math.h>
#include <nagc05.h>
#include <nagx02.h>

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

int main(int argc, char *argv[])
{
  FILE     *fpout;

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

  INIT_FAIL(fail);

  /* Check for command-line IO options */
  fpout = nag_example_file_io(argc, argv, "-results", NULL);


  fprintf(fpout, "nag_zero_nonlin_eqns_1 (c05tbc) Example Program Results\n");
  if (n > 0)
    {
      if (!(fvec = NAG_ALLOC(n, double)) ||
          !(x = NAG_ALLOC(n, double)))
        {
          fprintf(fpout, "Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  else
    {
      fprintf(fpout, "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)
    {
      fprintf(fpout, "Final approximate solution\n\n");
      for (j = 0; j < n; j++)
        fprintf(fpout, "%12.4f%s", x[j], (j%3 == 2 || j == n-1)?"\n":" ");
    }
  else
    {
      fprintf(fpout, "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)
        {
          fprintf(fpout, "Approximate solution\n\n");
          for (i = 0; i < n;  i++)
            fprintf(fpout, "%12.4f%s", x[i], (i%3 == 2 || i == n-1)?"\n":" ");
          exit_status = 2;
        }
    }
 END:
  if (fpout != stdout) fclose(fpout);
  if (fvec) NAG_FREE(fvec);
  if (x) NAG_FREE(x);
  return exit_status;
}
static void NAG_CALL 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;
    }
}