NAG Library Manual, Mark 27.2
```/* F01FC_T1W_F C++ Header Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
* Mark 27.2, 2021.
*/

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

int main(void)
{
int      exit_status = 0;
Integer  ifail       = 0;
NagError fail;
INIT_FAIL(fail);

cout << "F01FC_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.
Complex *          ac = 0;
nagad_t1w_w_rtype *ar = 0, *ai = 0;

a  = new nagad_t1w_w_ctype[n * n];
ar = new nagad_t1w_w_rtype[n * n];
ai = new nagad_t1w_w_rtype[n * n];
ac = new Complex[n * n];

// Read the matrix A, register and copy
double dr, di;

for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
cin >> dr >> di;
Integer k = i + j * n;
ar[k]     = dr;
ai[k]     = di;
}
}

// Create AD configuration data object
ifail = 0;

for (int l = 0; l < n; ++l)
{
{
double  inc            = 1.0;
Integer k              = l * n + l;
dco::derivative(ai[k]) = inc;
}
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
Integer k = i + j * n;
a[k].real(ar[k]);
a[k].imag(ai[k]);
}
}

// Find exp(A)
ifail = 0;

if (l == 0)
{
// Print exp(A)
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
int k = i + j * n;

ac[k].re = dco::value(real(a[k]));
ac[k].im = dco::value(imag(a[k]));
}
}

cout << endl;
x04dac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ac, n,
"  Exp(A)", 0, &fail);
}

for (int j = 0; j < n; j++)
{
Integer           k = j + j * n, p = l + j * n;
air      = real(a[k]);
aii      = imag(a[k]);
ac[p].re = dco::derivative(air);
ac[p].im = dco::derivative(aii);
}
{
double  zero           = 0.0;
Integer k              = l * n + l;
dco::derivative(ai[k]) = zero;
}
}
cout << "\n\n Derivatives calculated: First order tangents\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives of diagional of exp(A) w.r.t diagonal of imag(A):\n";

// Print derivatives
cout << endl;
x04dac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n, ac, n,
"     d(expA(i,i)/dImag(A(j,j))", 0, &fail);

// Remove computational data object
ifail = 0;

delete[] a;
delete[] ac;
delete[] ar;
delete[] ai;

return exit_status;
}
```