NAG Library Manual, Mark 28.4
```/* C05QS_A1W_F C++ Header Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
* Mark 28.4, 2022.
*/

#include <dco.hpp>
#include <iostream>
#include <math.h>
#include <nag.h>
#include <nagx02.h>
#include <nagx04.h>
#include <stdio.h>
#include <string>
using namespace std;

int main()
{
// Scalars
int           exit_status = 0;
const Integer n = 7, lrcomm = 12 + 3 * n, licomm = 8 * n + 19 + 3 * n;

cout << "C05QS_A1W_F C++ Header Example Program Results\n\n";

// problem parameters and starting value

ruser[0] = -1.0;
ruser[1] = 3.0;
ruser[2] = -2.0;
ruser[3] = -2.0;
ruser[4] = -1.0;

for (int i = 0; i < n; ++i)
{
x[i] = -1.0;
}

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

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

// Register variables to differentiate w.r.t.
for (int i = 0; i < 5; ++i)
{
dco::ga1s<double>::global_tape->register_variable(ruser[i]);
}

Integer           icomm[licomm];
logical           init = Nag_TRUE;

xtol = sqrt(X02AJC);
const Integer &         n,
const Integer &         lindf,
const Integer           indf[],
Integer &               iflag)
{
for (int ind = 0; ind < lindf; ++ind)
{
int i   = indf[ind] - 1;
fvec[i] = (ruser[1] + ruser[2] * x[i]) * x[i] - ruser[4];
if (i > 0)
fvec[i] = fvec[i] + ruser[0] * x[i - 1];
if (i < n - 1)
fvec[i] = fvec[i] + ruser[3] * x[i + 1];
}
iflag = 0;
};

ifail = 0;
nag::ad::c05qs(ad_handle, fcn, n, x, fvec, xtol, init, rcomm, lrcomm, icomm, licomm, ifail);

cout.setf(ios::scientific, ios::floatfield);
cout.precision(4);
cout << "           Solution:\n";
for (int i = 0; i < n; ++i)
{
cout.width(10);
cout << i + 1;
cout.width(20);
cout << dco::value(x[i]) << endl;
}

cout << "\n Derivatives calculated: First order adjoints\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives are of solution w.r.t function params\n\n";

// Setup evaluation of derivatives via adjoints
double dr[5 * n];
for (int i = 0; i < n; ++i)
{

double inc            = 1.0;
dco::derivative(x[i]) = inc;

ifail                                              = 0;
dco::ga1s<double>::global_tape->sparse_interpret() = true;

for (int j = 0; j < 5; ++j)
{
int k = j * n + i;
dr[k] = dco::derivative(ruser[j]);
}
}

NagError fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor, Nag_GeneralMatrix, Nag_NonUnitDiag, n, 5, dr, n,
"    dx/druser", 0, &fail);

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

return exit_status;
}
```