/* nag_ode_ivp_adams_roots(d02qfc) Example Program
 *
 * Copyright 1991 Numerical Algorithms Group.
 *
 * Mark 2, 1991.
 * Mark 7 revised, 2001.
 *
 */

#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)
{
  double y[NEQF], atol[NEQF], rtol[NEQF];
  Boolean crit, alter_g, vectol, one_step, sophist;
  double t, tout, tcrit;
  Integer i, max_step, neqf, neqg;
  Nag_Start state;
  Nag_ODE_Adams opt;

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

  neqf = NEQF;
  neqg = NEQG;
  tcrit = 10.0;
  state = Nag_NewStart;
  vectol = TRUE;
  one_step = FALSE;
  crit = TRUE;
  max_step = 0;
  sophist = TRUE;
  for (i = 0; i <= 1; ++i)
    {
      rtol[i] = 0.0001;
      atol[i] = 1e-06;
    }

  d02qwc(&state, neqf, vectol, atol, rtol, one_step, crit,
         tcrit, 0.0, max_step, neqg, &alter_g, sophist, &opt,
         NAGERR_DEFAULT);

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

  do
    {
      d02qfc(neqf, ftry02, &t, y, tout, gtry02, NAGUSER_DEFAULT, &opt,
             NAGERR_DEFAULT);

      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
   * d02qwc to the pointers inside opt.
   */
  d02qyc(&opt);

  return EXIT_SUCCESS;
}


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 */