NAG Library Manual, Mark 27.2
```/* D02PS_P0W_F C++ Header Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

#include <iostream>
#include <math.h>
#include <nag.h>
#include <stdio.h>
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, npts = 16, nwant = 1;
const Integer liwsav = 130;
const Integer lrwsav = 350 + 32 * n;
const Integer lwcomm = n + 5 * nwant;

Integer exit_status = 0;

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

cout << "D02PS_P0W_F C++ Header Example Program Results\n\n";

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

// Set initial conditions for ODE and parameters for the integrator.
Integer method = -1;
double  tol, hstart, tend, tstart;
tstart = 0.0;
tol    = 1.0e-4;
tend   = 2.0 * nag_math_pi;
hstart = 0.0;
for (int k = 0; k < n; k++)
{
thresh[k] = 1.0e-8;
}
ruser[0] = 1.0;
ruser[1] = 1.0;
y[0]     = 0.0;
y[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;
iwsav, rwsav, ifail);

double tnow, twant, tinc;
tinc  = (tend - tstart) / ((double)npts);
twant = tstart + tinc;
tnow  = tstart;
while (tnow < tend)
{
ifail = 0;
iwsav, rwsav, ifail);
while (twant <= tnow)
{
Integer ideriv = 2;
ifail          = 0;
wcomm, lwcomm, -1, iuser, -1, ruser, iwsav, rwsav,
ifail);

cout.width(6);
cout << twant;
cout.width(10);
cout << ywant[0];
cout.width(10);
cout << ypwant[0];
cout << endl;

twant = twant + tinc;
}
}

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[] ywant;
delete[] ypnow;
delete[] ypwant;
delete[] iwsav;
delete[] rwsav;
delete[] wcomm;
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];
}
```