```/* D01GA_A1W_F C++ Header Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
* Mark 27, 2019.
*/

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

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

cout << "D01GA_A1W_F C++ Header Example Program Results\n\n";

// Allocate memory
nagad_a1w_w_rtype *x = 0, *y = 0;

if (!(x = NAG_ALLOC(n, nagad_a1w_w_rtype)) ||
{
printf("Allocation failure\n");
exit_status = -2;
}

if (exit_status==0) {

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

/* Register variables to differentiate w.r.t. */
a = ar;

// 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);
}

ifail = 0;

double inc = 1.0;

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

// Get derivative
double da;

cout.setf(ios::scientific,ios::floatfield);
cout.setf(ios::right);
cout.precision(4);
cout << "\n Solution, 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 and tape