NAG Library Manual, Mark 27.2
```/* E01BF_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 <stdio.h>
#include <string>
using namespace std;

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

cout << "E01BF_T1W_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
nagad_t1w_w_rtype *x = 0, *f = 0, *d = 0;
double *           dx = 0, *df = 0;
dx = new double[n];
df = new double[n];

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

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

for (int i = 0; i < 2 * n; ++i)
{
double inc = 1.0;
if (i < n)
{
dco::derivative(x[i]) = inc;
}
else
{
dco::derivative(f[i - n]) = inc;
}
ifail = 0;

// Evaluate interpolant and derivatives at a mid-point
const Integer     m = 1;
double            xint;
xint  = 0.5 * (dco::value(x[n / 2 - 1]) + dco::value(x[n / 2]));
px[0] = xint;

ifail = 0;

double zero = 0.0;
if (i < n)
{
dx[i]                 = dco::derivative(pf[0]);
dco::derivative(x[i]) = zero;
}
else
{
df[i - n]                 = dco::derivative(pf[0]);
dco::derivative(f[i - n]) = zero;
}

if (i == 0)
{
cout << "\n Value of interpolant at x = " << xint;
cout.precision(5);
cout << " is: " << dco::value(pf[0]) << endl;
}
}

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

// Get derivatives
cout << "\n Derivatives of fitted value w.r.t. data points:\n\n";
cout << "    i     d/dx         d/df\n";
cout.setf(ios::scientific, ios::floatfield);
cout.precision(4);
for (int j = 0; j < n; j++)
{
cout.width(5);
cout << j + 1;
cout.width(12);
cout << dx[j];
cout.width(12);
cout << df[j] << endl;
}

// Remove computational data object and tape