/* nag_ode_ivp_adams_interp (d02qzc) 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 ftry03(Integer neqf, double x, const double y[],
                            double yp[], Nag_User *comm);
#ifdef __cplusplus
}
#endif

#define NEQF 2
#define TSTART 0.0

int main(void) {
  static Integer use_comm[1] = {1};
  Nag_Boolean alter_g, crit, one_step, sophist, vectol;
  Integer exit_status = 0, i, j, max_step, neqf, neqg, nwant;
  NagError fail;
  Nag_ODE_Adams opt;
  Nag_Start state;
  Nag_User comm;
  double *atol = 0, hmax, pi, *rtol = 0, t, tcrit, tinc, tout, twant, *y = 0;
  double *ypwant = 0, *ywant = 0;

  INIT_FAIL(fail);

  printf("nag_ode_ivp_adams_interp (d02qzc) Example Program Results\n");

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

  /* nag_math_pi (x01aac).
   * pi
   */
  pi = nag_math_pi;
  state = Nag_NewStart;
  neqf = NEQF;
  if (neqf >= 1) {
    if (!(atol = NAG_ALLOC(neqf, double)) ||
        !(rtol = NAG_ALLOC(neqf, double)) || !(y = NAG_ALLOC(neqf, double)) ||
        !(ywant = NAG_ALLOC(neqf, double)) ||
        !(ypwant = NAG_ALLOC(neqf, double))) {
      printf("Allocation failure\n");
      exit_status = -1;
      goto END;
    }
  } else {
    exit_status = 1;
    return exit_status;
  }

  neqg = 0;
  sophist = Nag_FALSE;
  vectol = Nag_TRUE;
  for (i = 0; i < 2; ++i) {
    atol[i] = 1e-08;
    rtol[i] = 0.0001;
  }
  one_step = Nag_TRUE;
  crit = Nag_TRUE;
  tinc = pi * 0.0625;
  tcrit = tinc * 8.0;
  tout = tcrit;
  max_step = 500;
  hmax = 2.0;
  t = TSTART;
  twant = TSTART + tinc;
  nwant = 2;
  y[0] = 0.0;
  y[1] = 1.0;
  printf("\n   T        Y(1)    Y(2)\n");
  printf(" %6.4f   %7.4f %7.4f  \n", t, y[0], y[1]);

  /* 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, hmax, 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;
  }

  j = 1;

  while (t < tout && fail.code == NE_NOERROR) {
    /* nag_ode_ivp_adams_roots (d02qfc).
     * Ordinary differential equation solver using Adams method
     * (sophisticated use)
     */
    nag_ode_ivp_adams_roots(neqf, ftry03, &t, y, tout, NULLDFN, &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;
    }

    while (twant <= t && fail.code == NE_NOERROR) {
      /* nag_ode_ivp_adams_interp (d02qzc).
       * Interpolation function for use with
       * nag_ode_ivp_adams_roots (d02qfc)
       */
      nag_ode_ivp_adams_interp(neqf, twant, nwant, ywant, ypwant, &opt, &fail);
      if (fail.code != NE_NOERROR) {
        printf("Error from nag_ode_ivp_adams_interp (d02qzc).\n%s\n",
               fail.message);
        exit_status = 1;
        goto END;
      }

      printf(" %6.4f   %7.4f %7.4f  \n", twant, ywant[0], ywant[1]);
      ++j;
      twant = (double)j * tinc + 0.0;
    }
  }
  /* 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(atol);
  NAG_FREE(rtol);
  NAG_FREE(y);
  NAG_FREE(ywant);
  NAG_FREE(ypwant);
  return exit_status;
}

static void NAG_CALL ftry03(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 ftry03, first invocation.)\n");
    use_comm[0] = 0;
  }

  yp[0] = y[1];
  yp[1] = -y[0];
} /* ftry03 */