NAG Library Manual, Mark 28.4
```/* F07AE_A1W_F C++ Header Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
* Mark 28.4, 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 << "F07AE_A1W_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, nrhs;
cin >> n >> nrhs;

// Allocate arrays containing A and its factorized form, B
// and the solution X.
nagad_a1w_w_rtype *a = 0, *a_in = 0, *b = 0, *b_in = 0;
double *           ar = 0, *br = 0;
Integer *          ipiv = 0;
a                       = new nagad_a1w_w_rtype[n * n];
a_in                    = new nagad_a1w_w_rtype[n * n];
b                       = new nagad_a1w_w_rtype[n * nrhs];
b_in                    = new nagad_a1w_w_rtype[n * nrhs];
ipiv                    = new Integer[n];
ar                      = new double[n * n];
br                      = new double[n * nrhs];

dco::ga1s<double>::global_tape = dco::ga1s<double>::tape_t::create();

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

// Read the matrix B, register and copy
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < nrhs; ++j)
{
cin >> dd;
Integer k = i + j * n;
b_in[k]   = dd;
if (j == 0)
{
dco::ga1s<double>::global_tape->register_variable(b_in[k]);
}
b[k] = b_in[k];
}
}

// Create AD configuration data object
ifail = 0;

// Factorize the matrix A
ifail = 0;

// Solve AX = B
ifail = 0;

// Print Solution
for (int i = 0; i < n; i++)
{
for (int j = 0; j < nrhs; j++)
{
int k = i + j * n;
br[k] = dco::value(b[k]);
}
}
NagError fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, nrhs, br, n,
"  Solution", 0, &fail);

cout << "\n Derivatives calculated: First order adjoints\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives of solution X w.r.t. RHS B (A inverse)\n";

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

double inc = 1.0;
dco::derivative(b[i]) += inc;
ifail                                              = 0;
dco::ga1s<double>::global_tape->sparse_interpret() = true;

for (int j = 0; j < n; j++)
{
dd            = dco::derivative(b_in[j]);
ar[i + j * n] = dd;
}
}
// Print derivatives
cout << endl;
INIT_FAIL(fail);
x04cac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ar, n,
"           dx(i,1)/db(j,1)", 0, &fail);

ifail = 0;

dco::ga1s<double>::tape_t::remove(dco::ga1s<double>::global_tape);

delete[] a;
delete[] a_in;
delete[] b;
delete[] b_in;
delete[] ipiv;
delete[] ar;
delete[] br;
return exit_status;
}
```