NAG Library Manual, Mark 27.3
Interfaces:  FL   CL   CPP   AD
```/* E01EA_P0W_F C++ Header Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
* Mark 27.3, 2021.
*/

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

int main()
{
// Scalars
int exit_status = 0;

cout << "E01EA_P0W_F C++ Header Example Program Results\n\n";

// Skip first line of data file
string mystr;
getline(cin, mystr);
// Read number of data points
Integer n;
cin >> n;

// Allocate arrays for data and interpolant
double * x = 0, *y = 0, *f = 0;
Integer *triang = 0;
x               = new double[n];
y               = new double[n];
f               = new double[n];
triang          = new Integer[7 * n];

// Read data variables
for (int i = 0; i < n; i++)
{
double xr, yr, fr;
cin >> xr >> yr >> fr;
x[i] = xr;
y[i] = yr;
f[i] = fr;
}

Integer           ifail = 0;
nag::ad::e01ea(n, x, y, triang, ifail);

double px[1], py[1], pf[1];
double xint, yint;
xint  = 0.5 * (x[n / 2 - 1] + x[n / 2]);
yint  = 0.5 * (y[n / 2 - 1] + y[n / 2]);
px[0] = xint;
py[0] = yint;

// Call the passive routine
Integer m = 1;
ifail     = 0;
nag::ad::e01eb(ad_handle, m, n, x, y, f, triang, px, py, pf, ifail);

cout << "\n Interpolant point: x = " << xint << " y = " << yint << endl;
cout.precision(5);
cout << " Interpolated value = " << pf[0] << endl;

delete[] x;
delete[] y;
delete[] f;
delete[] triang;
return exit_status;
}
```