/* nag_ode_ivp_adams_roots (d02qfc) 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 <nagd02.h>

#ifdef __cplusplus
extern "C" {
#endif
  static void ftry02(Integer neqf, double x, double y[], double yp[],
                     Nag_User *comm);
  static double gtry02(Integer neqf, double x, double y[], double yp[],
                       Integer k, Nag_User *comm);
#ifdef __cplusplus
}
#endif

#define NEQF 2
#define NEQG 2
int main(void)
{
  Nag_Boolean alter_g, crit, one_step, sophist, vectol;
  Integer exit_status=0, i, max_step, neqf, neqg;
  NagError fail;
  Nag_ODE_Adams opt;
  Nag_Start state;
  double *atol=0, *rtol=0, t, tcrit, tout, *y=0;

  INIT_FAIL(fail);

  Vprintf("nag_ode_ivp_adams_roots (d02qfc) Example Program Results\n");

  neqf = NEQF;
  neqg = NEQG;
  if (neqf<1)
    {
      exit_status = 1;
      return exit_status;
    }
  else
    {
      if ( !( y = NAG_ALLOC(neqf, double)) ||
           !( atol = NAG_ALLOC(neqf, double)) ||
           !( rtol = NAG_ALLOC(neqf, double)) )
        {
          Vprintf("Allocation failure\n");
          exit_status = -1;
          goto END;
        }
    }
  tcrit = 10.0;
  state = Nag_NewStart;
  vectol = Nag_TRUE;
  one_step = Nag_FALSE;
  crit = Nag_TRUE;
  max_step = 0;
  sophist = Nag_TRUE;
  for (i = 0; i <= 1; ++i)
    {
      rtol[i] = 0.0001;
      atol[i] = 1e-06;
    }

  /* nag_ode_ivp_adams_setup (d02qwc).
   * Setup function for nag_ode_ivp_adams_roots (d02qfc)
   */
  nag_ode_ivp_adams_setup(&state, neqf, vectol, atol, rtol, one_step, crit,
                          tcrit, 0.0, max_step, neqg, &alter_g, sophist, &opt,
                          &fail);
  if (fail.code != NE_NOERROR)
    {
      Vprintf("Error from nag_ode_ivp_adams_setup (d02qwc).\n%s\n",
              fail.message);
      exit_status = 1;
      goto END;
    }

  t = 0.0;
  tout = tcrit;
  y[0] = 0.0;
  y[1] = 1.0;

  do
    {
      /* nag_ode_ivp_adams_roots (d02qfc).
       * Ordinary differential equation solver using Adams method
       * (sophisticated use)
       */
      nag_ode_ivp_adams_roots(neqf, ftry02, &t, y, tout, gtry02,
                              NAGUSER_DEFAULT, &opt, &fail);
      if (fail.code != NE_NOERROR)
        {
          Vprintf("Error from nag_ode_ivp_adams_roots (d02qfc).\n%s\n",
                  fail.message);
          exit_status = 1;
          goto END;
        }


      if (opt.root)
        {
          Vprintf("\nRoot at %11.5e\n", t);
          Vprintf("for event equation %1ld", opt.index);
          Vprintf(" with type %1ld", opt.type);
          Vprintf(" and residual %11.5e\n", opt.resids[opt.index-1]);

          Vprintf(" Y(1) = %11.5e   Y'(1) = %11.5e\n", y[0], opt.yp[0]);

          for (i = 1; i <= neqg; ++i)
            {
              if (i != opt.index && opt.events[i-1] != 0)
                {
                  Vprintf("and also for event equation %1ld", i);
                  Vprintf(" with type %1ld", opt.events[i-1]);
                  Vprintf(" and residual %11.5e\n", opt.resids[i-1]);
                }
            }
        }

    } while (opt.tcurr < tout && opt.root);

  /* Free the memory which was allocated by
   * nag_ode_ivp_adams_setup (d02qwc) to the pointers inside opt.
   */
  /* nag_ode_ivp_adams_free (d02qyc).
   * Freeing function for use with nag_ode_ivp_adams_roots
   * (d02qfc)
   */
  nag_ode_ivp_adams_free(&opt);
 END:
  if (y) NAG_FREE(y);
  if (atol) NAG_FREE(atol);
  if (rtol) NAG_FREE(rtol);
  return exit_status;
}
static void ftry02(Integer neqf, double x, double y[], double yp[],
                   Nag_User *comm)
{
  yp[0] = y[1];
  yp[1] = -y[0];
}                               /* ftry02 */
static double gtry02(Integer neqf, double x, double y[], double yp[],
                     Integer k, Nag_User *comm)
{
  if (k == 1) return yp[0];
  else return y[0];
}  /* gtry02 */