NAG Library Manual, Mark 28.6
```/* F07FJ_T1W_F C++ Header Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
* Mark 28.6, 2022.
*/

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

int main()
{
int               exit_status = 0;
Integer           ifail = 0;

cout << "F07FJ_T1W_F C++ Header Example Program Results\n\n";
// Skip heading in data file
string mystr;
getline(cin, mystr);

// Read problem size and number of right-hand-sides
Integer n;
cin >> n;

// Allocate arrays containing A and its factorized form, B
// and the solution X.
nagad_t1w_w_rtype *a = 0, *ax = 0;
double *           ar = 0, *dr = 0;
a  = new nagad_t1w_w_rtype[n * n];
ax = new nagad_t1w_w_rtype[n * n];
ar = new double[n * n];
dr = new double[n * n];

// Read the lower triangular matrix A, register and copy
double dd;
for (int i = 0; i < n; ++i)
{
for (int j = 0; j <= i; ++j)
{
cin >> dd;
int k = i + j * n;
a[k]  = dd;
ax[k] = a[k];
}
}

// Create AD configuration data object
ifail = 0;

for (int i = 0; i < n; ++i)
{

double inc = 1.0, zero = 0.0;
dco::derivative(a[i * n + i]) = inc;

for (int l = 0; l < n; ++l)
{
for (int j = 0; j <= l; ++j)
{
int k = l + j * n;
ax[k] = a[k];
}
}
// Factorize the matrix A
ifail = 0;

// Get the inverse of A
ifail = 0;
dco::derivative(a[i * n + i]) = zero;
for (int j = 0; j < n; j++)
{
double dd     = dco::derivative(ax[j * n + j]);
dr[i + j * n] = dd;
}
}

// Print inverse
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
int k = i + j * n;
ar[k] = dco::value(ax[k]);
}
}
cout << endl;
NagError fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ar, n,
"  Inverse", 0, &fail);

cout << "\n\n Derivatives calculated: First order adjoints\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives of Ainv_ii w.r.t A_jj:\n";

// Print derivatives
cout << endl;
x04cac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, dr, n,
"  Derivatives dAinv(i,i)/dA(j,j)", 0, &fail);

ifail = 0;

delete[] a;
delete[] ax;
delete[] ar;
delete[] dr;
return exit_status;
}
```