/* D02PQ_P0W_F C++ Header Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
*
* Mark 27.1, 2020.
*/

#include <nag.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 << "D02PQ_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;

Integer ifail = 0;

// Initialize Runge-Kutta method for integrating ODE
ifail = 0;
iwsav,rwsav,ifail);

double tnow;
tnow = tstart;
while (tnow<tend) {
ifail = 0;
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;
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];
}