/* nag_zero_nonlin_eqns_rcomm (c05qdc) Example Program.
 *
 * Copyright 2014 Numerical Algorithms Group.
 *
 * Mark 25, 2014.
 */

#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 fcn(Integer n, const double x[], double fvec[]);
#ifdef __cplusplus
}
#endif

int main(void)
{
  Integer  exit_status = 0, i, n = 9, irevcm, ml, mu;
  double   *diag = 0, *fjac = 0, *fvec = 0, *qtf = 0, *r = 0, *x = 0,
           *rwsav = 0;
  Integer  *iwsav = 0;
  double   epsfcn, factor, xtol;
  /* Nag Types */
  NagError fail;
  Nag_ScaleType scale_mode;

  INIT_FAIL(fail);

  printf("nag_zero_nonlin_eqns_rcomm (c05qdc) Example Program Results\n");
  if (n > 0)
    {
      if (!(diag = NAG_ALLOC(n, double)) ||
          !(fjac = NAG_ALLOC(n*n, double)) ||
          !(fvec = NAG_ALLOC(n, double)) ||
          !(qtf = NAG_ALLOC(n, double)) ||
          !(r = NAG_ALLOC(n*(n+1)/2, double)) ||
          !(x = NAG_ALLOC(n, double)) ||
          !(iwsav = NAG_ALLOC(17, Integer)) ||
          !(rwsav = NAG_ALLOC(4*n + 10, double)))
        {
          printf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  else
    {
      printf("Invalid n.\n");
      exit_status = 1;
      goto END;
    }

  /* The following starting values provide a rough solution. */
  for (i = 0; i < n; i++)
    x[i] = -1.0;

  /* nag_machine_precision (x02ajc).
   * The machine precision
   */
  xtol = sqrt(nag_machine_precision);

  for (i = 0; i < n; i++)
    diag[i] = 1.0;

  ml = 1;
  mu = 1;
  epsfcn = 0.0;
  scale_mode = Nag_ScaleProvided;
  factor = 100.0;
  irevcm = 0;

  /* nag_zero_nonlin_eqns_rcomm (c05qdc).
   * Solution of a system of nonlinear equations (function values only,
   * reverse communication)
   */

  do
    {
      nag_zero_nonlin_eqns_rcomm(&irevcm, n, x, fvec, xtol, ml, mu,
                                 epsfcn, scale_mode, diag, factor, fjac, r,
                                 qtf, iwsav, rwsav, &fail);

      switch (irevcm)
        {
        case 1:
          /* x and fvec are available for printing */
          break;
        case 2:
          fcn(n, x, fvec);
          break;
        }

    } while (irevcm != 0);

  if (fail.code != NE_NOERROR)
    {
      printf("Error from nag_zero_nonlin_eqns_rcomm (c05qdc).\n%s\n",
             fail.message);
      exit_status = 1;
      if (fail.code != NE_TOO_SMALL &&
          fail.code != NE_NO_IMPROVEMENT)
        goto END;
    }

  printf(fail.code == NE_NOERROR ? "Final approximate" : "Approximate");
  printf(" solution\n\n");
  for (i = 0; i < n;  i++)
    printf("%12.4f%s", x[i], (i%3 == 2 || i == n-1)?"\n":" ");

  if (fail.code != NE_NOERROR)
    exit_status = 2;

 END:
  NAG_FREE(diag);
  NAG_FREE(fjac);
  NAG_FREE(fvec);
  NAG_FREE(qtf);
  NAG_FREE(r);
  NAG_FREE(x);
  NAG_FREE(iwsav);
  NAG_FREE(rwsav);
  return exit_status;
}
static void NAG_CALL fcn(Integer n, const double x[], double fvec[])
{
  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;
    }
}