NAG Library Manual, Mark 27.2
Interfaces:  FL   CL   CPP   AD
```/* D01GA_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>
using namespace std;

int main(void)
{
// Scalars
int     exit_status = 0;
Integer n           = 21;
double  ar          = 1.0;

cout << "D01GA_T1W_F C++ Header Example Program Results\n\n";

// Allocate memory
nagad_t1w_w_rtype *x = 0, *y = 0;

x = new nagad_t1w_w_rtype[n];
y = new nagad_t1w_w_rtype[n];

// Create AD configuration data object
Integer ifail     = 0;
void *  ad_handle = 0;

a = ar;

double inc         = 1.0;
dco::derivative(a) = inc;

// Initialize variables
for (int i = 0; i < n; i++)
{
double            xr = (1.0 * i) / (1.0 * (n - 1));
x[i] = xr;
tmp  = a * x[i];
y[i] = 4.0 / (1.0 + tmp * tmp);
}

// Call the AD routine
ifail = 0;

nag::ad::d01ga(ad_handle, x, y, n, ans, er, ifail);

double da;
da = dco::derivative(ans);

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

cout.setf(ios::scientific, ios::floatfield);
cout.setf(ios::right);
cout.precision(4);
cout << "\n Solution, ans = ";
double ans_value = dco::value(ans);
cout.width(12);
cout << ans_value << endl;
cout << "\n Derivative:\n";
cout << " d(ans)/da = ";
cout.width(12);
cout << da << endl;

// Remove computational data object