/* D02PT_P0W_F C++ Header Example Program.
 *
 * Copyright 2020 Numerical Algorithms Group.
 *
 * Mark 27.1, 2020.
 */

#include <nag.h>
#include <nagad.h>
#include <math.h>
#include <stdio.h>
#include <iostream>
using namespace std;

#ifdef __cplusplus
extern "C"
{
#endif
  static void NAG_CALL f(void * &ad_handle, const double &t,
                         const Integer &n, const double y[],
                         double yp[], Integer iuser[], double ruser[]);
#ifdef __cplusplus
}
#endif

int main(void)
{
  const Integer     n = 2;
  const Integer     liwsav = 130;
  const Integer     lrwsav = 350 + 32 * n;

  Integer           exit_status = 0;

  double            *rwsav = 0, *thresh = 0, *ynow = 0;
  double            *ypnow = 0, *y = 0, ruser[2];
  Integer           *iwsav = 0, iuser[1];

  cout << "D02PT_P0W_F C++ Header Example Program Results\n\n";

  thresh = new double [n];
  ynow   = new double [n];
  y      = new double [n];
  ypnow  = new double [n];
  iwsav  = new Integer [liwsav];
  rwsav  = new double [lrwsav];

  // Set initial conditions for ODE and parameters for the integrator.
  Integer           method = 2;
  double            tol, hstart, tend, tstart;
  tstart    = 0.0;
  tol       = 1.0e-4;
  tend      = 2.0*nag_math_pi;
  y[0]      = 0.0;
  y[1]      = 1.0;
  hstart    = 0.0;
  thresh[0] = 1.0e-8;
  thresh[1] = 1.0e-8;
  ruser[0]  = 1.0;
  ruser[1]  = 1.0;
  
  cout << "\n  Calculation with tol = " << tol << endl;
  cout.setf(ios::fixed);
  cout.setf(ios::right);

  cout.precision(3);
  cout << "\n    t         y1        y2" << endl;
  cout.width(6); cout << tstart;
  
  for (int k = 0; k < n; k++) {
    cout.width(10); cout << y[k];
  }
  cout << endl;

  // Initialize Runge-Kutta method for integrating ODE
  Integer ifail = 0;
  void    *ad_handle = 0;
  d02pq_p0w_f_(ad_handle,n,tstart,tend,y,tol,thresh,method,hstart,
               iwsav,rwsav,ifail);

  double  tnow;
  tnow = tstart;
  while (tnow<tend) {
    ifail = 0;
    d02pf_p0w_f_(ad_handle,f,n,tnow,ynow,ypnow,iuser,ruser,
                 iwsav,rwsav,ifail);
    cout.width(6); cout << tnow;
    for (int k = 0; k < n; ++k) {
      cout.width(10); cout << ynow[k];
    }
    cout << endl;
  }

  double            hnext, waste;
  Integer           fevals, stepcost, stepsok;
  ifail = 0;
  d02pt_p0w_f_(ad_handle,fevals,stepcost,waste,stepsok,hnext,iwsav,
               rwsav,ifail);
  cout << "\n Cost of the integration in evaluations of f is " << fevals;
  cout << endl;

  delete [] thresh;
  delete [] ynow;
  delete [] y;
  delete [] ypnow;
  delete [] iwsav;
  delete [] rwsav;
  return exit_status;
}

static void NAG_CALL f(void * &ad_handle, const double &t,
                       const Integer &n, const double y[],
                       double yp[], Integer iuser[], double ruser[])
{
  yp[0] = ruser[0]*y[1];
  yp[1] = -ruser[1]*y[0];
}