NAG Library Manual, Mark 28.7
```/* F07AR_A1W_F C++ Header Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
* Mark 28.7, 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 << "F07AR_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;
cin >> n;

// Allocate arrays containing A and its factorized form, B
// and the solution X.
nagad_a1w_w_ctype *a = 0, *a_in = 0, *work = 0;
nagad_a1w_w_rtype *a_r = 0, *a_i = 0;
Complex *          ar    = 0;
Integer *          ipiv  = 0;
Integer            lwork = 64 * n;
a                        = new nagad_a1w_w_ctype[n * n];
a_in                     = new nagad_a1w_w_ctype[n * n];
a_r                      = new nagad_a1w_w_rtype[n * n];
a_i                      = new nagad_a1w_w_rtype[n * n];
ipiv                     = new Integer[n];
ar                       = new Complex[n * n];

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

// Read the matrix A, register and copy
double            dr, di;
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
Integer k = i + j * n;
cin >> dr >> di;
a_r[k] = dr;
a_i[k] = di;
dco::ga1s<double>::global_tape->register_variable(a_r[k]);
dco::ga1s<double>::global_tape->register_variable(a_i[k]);
a[k].real(a_r[k]);
a[k].imag(a_i[k]);
ar[k].re = dr;
ar[k].im = di;
}
}

// Print matrix A
NagError fail;
INIT_FAIL(fail);
x04dac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ar, n, "  A",
0, &fail);

// Create AD configuration data object
ifail = 0;

// Factorize the matrix A
ifail = 0;

// Invert A
ifail = 0;

// Print Inverse
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
int               k = i + j * n;
akr      = real(a[k]);
aki      = imag(a[k]);
ar[k].re = dco::value(akr);
ar[k].im = dco::value(aki);
}
}
cout << endl;
// NagError  fail;
INIT_FAIL(fail);
x04dac(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 inverse diagonal w.r.t diagonal of A:\n";

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

double  inc = 1.0;
Integer k   = i * n + i;

dar = real(a[k]);
dco::derivative(dar) += inc;
ifail                                              = 0;
dco::ga1s<double>::global_tape->sparse_interpret() = true;

for (int j = 0; j < n; j++)
{
Integer k        = j + j * n;
double  dr       = dco::derivative(a_r[k]);
double  di       = dco::derivative(a_i[k]);
ar[i + j * n].re = dr;
ar[i + j * n].im = di;
}
}
// Print derivatives
cout << endl;
INIT_FAIL(fail);
x04dac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ar, n,
"   d(real(ai(i,i)))/da(j,j)", 0, &fail);

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

double  inc = 1.0;
Integer k   = i * n + i;

dar = imag(a[k]);
dco::derivative(dar) += inc;
ifail                                              = 0;
dco::ga1s<double>::global_tape->sparse_interpret() = true;

for (int j = 0; j < n; j++)
{
Integer k        = j + j * n;
double  dr       = dco::derivative(a_r[k]);
double  di       = dco::derivative(a_i[k]);
ar[i + j * n].re = dr;
ar[i + j * n].im = di;
}
}
// Print derivatives
cout << endl;
INIT_FAIL(fail);
x04dac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ar, n,
"   d(real(ai(i,i)))/da(j,j)", 0, &fail);

ifail = 0;

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

delete[] a;
delete[] a_in;
delete[] a_r;
delete[] a_i;
delete[] work;
delete[] ipiv;
delete[] ar;
return exit_status;
}
```