NAG Library Manual, Mark 27.2
```/* D01PA_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;

extern "C"
{
static void NAG_CALL functn(void *&        ad_handle,
const Integer &ndim,
const double   x[],
double &       ret,
Integer        iuser[],
double         ruser[]);
}

int main(void)
{
// Scalars
int     exit_status = 0;
Integer mxord = 5, ndim = 3, sdvert = 8, ldvert = 4;

cout << "D01PA_P0W_F C++ Header Example Program Results\n\n";

// Allocate memory
double *finvls = 0, *vert = 0, *vert_in = 0;
finvls = new double[mxord];
vert   = new double[ldvert * sdvert];

for (int i = 0; i < ndim * ldvert; i++)
{
vert[i] = 0.0;
}
for (int i = 1; i < ndim * ldvert; i = i + ldvert + 1)
{
vert[i] = 1.0;
}

cout << "\n Maxord   Estimated      Estimated         Integrand\n";
cout << "           value         accuracy        evaluations\n";
cout.setf(ios::scientific, ios::floatfield);
cout.precision(4);
Integer minord = 0, nevals = 1;
for (Integer maxord = 1; maxord <= mxord; maxord++)
{

// Call the passive routine
double  esterr, ruser[1];
Integer iuser[1];
Integer ifail = 0;

maxord, finvls, esterr, -1, iuser, -1, ruser, ifail);
double finv_r = finvls[maxord - 1];
cout.width(5);
cout << maxord;
cout.width(15);
cout << finv_r;
cout.width(15);
cout << esterr;
cout.width(12);
cout << nevals << endl;

nevals = (nevals * (maxord + ndim + 1)) / maxord;
}

cout.setf(ios::right);
cout.precision(4);
cout << "\n Solution, I = ";
double ans_value = finvls[mxord - 1];
cout.width(12);
cout << ans_value << endl;

delete[] finvls;
delete[] vert;
return exit_status;
}
static void NAG_CALL functn(void *&        ad_handle,
const Integer &ndim,
const double   x[],
double &       ret,
Integer        iuser[],
double         ruser[])
{
double tmp1;
tmp1 = x[0] + x[1] + x[2];
ret  = exp(tmp1) * cos(tmp1);
return;
}
```