/* nag_ode_ivp_adams_roots (d02qfc) Example Program.
 *
 * Copyright 2024 Numerical Algorithms Group.
 *
 * Mark 30.2, 2024.
 *
 */

#include <nag.h>
#include <stdio.h>

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

#define NEQF 2
#define NEQG 2
int main(void) {
  static Integer use_comm[2] = {1, 1};
  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;
  Nag_User comm;
  double *atol = 0, *rtol = 0, t, tcrit, tout, *y = 0;

  INIT_FAIL(fail);

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

  /* For communication with user-supplied functions: */
  comm.p = (Pointer)&use_comm;

  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))) {
      printf("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) {
    printf("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, &comm, &opt,
                            &fail);
    if (fail.code != NE_NOERROR) {
      printf("Error from nag_ode_ivp_adams_roots (d02qfc).\n%s\n",
             fail.message);
      exit_status = 1;
      goto END;
    }

    if (opt.root) {
      printf("\nRoot at %14.5e\n", t);
      printf("for event equation %1" NAG_IFMT "", opt.index);
      printf(" with type %1" NAG_IFMT "", opt.type);
      printf(" and residual %14.5e\n", opt.resids[opt.index - 1]);

      printf(" Y(1) = %14.5e   Y'(1) = %14.5e\n", y[0], opt.yp[0]);

      for (i = 1; i <= neqg; ++i) {
        if (i != opt.index && opt.events[i - 1] != 0) {
          printf("and also for event equation %1" NAG_IFMT "", i);
          printf(" with type %1" NAG_IFMT "", opt.events[i - 1]);
          printf(" and residual %14.5e\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_rootdiag (d02qyc).
   * Freeing function for use with nag_ode_ivp_adams_roots (d02qfc)
   */
  nag_ode_ivp_adams_rootdiag(&opt);
END:
  NAG_FREE(y);
  NAG_FREE(atol);
  NAG_FREE(rtol);
  return exit_status;
}

static void NAG_CALL ftry02(Integer neqf, double x, const double y[],
                            double yp[], Nag_User *comm) {
  Integer *use_comm = (Integer *)comm->p;

  if (use_comm[0]) {
    printf("(User-supplied callback ftry02, first invocation.)\n");
    use_comm[0] = 0;
  }

  yp[0] = y[1];
  yp[1] = -y[0];
} /* ftry02 */

static double NAG_CALL gtry02(Integer neqf, double x, const double y[],
                              double const yp[], Integer k, Nag_User *comm) {
  Integer *use_comm = (Integer *)comm->p;

  if (use_comm[1]) {
    printf("(User-supplied callback gtry02, first invocation.)\n");
    use_comm[1] = 0;
  }

  if (k == 1)
    return yp[0];
  else
    return y[0];
} /* gtry02 */