NAG Library Manual, Mark 27.2
```/* E02DE_T1W_F C++ Header Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
* Mark 27.2, 2021.
*/

#include <dco.hpp>
#include <iostream>
#include <math.h>
#include <nag.h>
#include <nagx04.h>
#include <stdio.h>
#include <string>
using namespace std;

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

cout << "E02DE_T1W_F C++ Header Example Program Results\n\n";

// Skip first line of data file
string mystr;
getline(cin, mystr);
// Read number of x and y data points
Integer mx, my;
cin >> mx;
cin >> my;

// Allocate arrays for data and interpolant
nagad_t1w_w_rtype *x = 0, *lamda = 0, *y = 0, *mu = 0, *f = 0, *c = 0,
*wrk = 0;
Integer *iwrk          = 0;
Integer  lwrk          = (my + 6) * (mx + 6);
lamda                  = new nagad_t1w_w_rtype[mx + 4];
mu                     = new nagad_t1w_w_rtype[my + 4];
f                      = new nagad_t1w_w_rtype[my * mx];
c                      = new nagad_t1w_w_rtype[my * mx];
iwrk                   = new Integer[lwrk];

// Create AD configuration data object
Integer ifail     = 0;

// Read data and register variables
for (int i = 0; i < mx; i++)
{
double xr;
cin >> xr;
x[i] = xr;
}
for (int i = 0; i < my; i++)
{
double yr;
cin >> yr;
y[i] = yr;
}
for (int i = 0; i < my; i++)
{
double fr;
for (int j = 0; j < mx; j++)
{
Integer k = j * my + i;
cin >> fr;
f[k] = fr;
}
}

Integer px, py;
ifail = 0;
nag::ad::e01da(ad_handle, mx, my, x, y, f, px, py, lamda, mu, c, wrk, ifail);

// Evaluate interpolant and derivatives at an internal point
const Integer     m = 1;
tx[0] = 1.4;
ty[0] = 0.5;

double inc = 1.0, zero = 0.0;
dco::derivative(tx[0]) = inc;
ifail                  = 0;
nag::ad::e02de(ad_handle, m, px, py, tx, ty, lamda, mu, c, ff, wrk, iwrk,
ifail);
double dx              = dco::derivative(ff[0]);
dco::derivative(tx[0]) = zero;

dco::derivative(tx[0]) = inc;
ifail                  = 0;
nag::ad::e02de(ad_handle, m, px, py, tx, ty, lamda, mu, c, ff, wrk, iwrk,
ifail);
double dy = dco::derivative(ff[0]);

cout << "\n Interpolant evaluated at x = " << dco::value(tx[0]);
cout << " and y = " << dco::value(ty[0]);
cout.precision(5);
cout << "\n Value of interpolant       = ";
cout << dco::value(ff[0]) << endl;

cout << "\n Derivatives calculated: First order tangents\n";
cout << " Computational mode    : algorithmic\n";

cout << "\n Derivatives of fitted value w.r.t. fit point:\n\n";
cout << "   dfit/dx = " << dx << endl;
cout << "   dfit/dy = " << dy << endl;

// Remove computational data object