```/* F11DB_A1W_F C++ Header Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
* Mark 27.1, 2020.
*/
#include <dco_light.hpp>
#include <nag.h>
#include <nagx04.h>
#include <stdio.h>
#include <iostream>
using namespace std;

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

cout << "F11DB_A1W_F C++ Header Example Program Results\n\n";
// Skip heading in data file
string mystr;
getline (cin, mystr);

// Read order of matrix and number of nonzero entries
Integer           n, nnz;
cin >> n;
cin >> nnz;

Integer           la = 2*nnz;
Integer           liwork = 7*n + 2;
double            *ar=0, *yr=0, *dxdy=0;
Integer           *icol=0, *idiag=0, *ipivp=0, *ipivq=0, *irow=0;
Integer           *istr=0, *iwork=0;

icol  = new Integer [la];
idiag = new Integer [n];
ipivp = new Integer [n];
ipivq = new Integer [n];
irow  = new Integer [la];
istr  = new Integer [n+1];
iwork = new Integer [liwork];
ar    = new double [la];
yr    = new double [n];
dxdy  = new double [n*n];

for (int i=0; i<nnz; i++) {
cin >> ar[i] >> irow[i] >> icol[i];
a[i] = ar[i];
}

for (int i=0; i<n; i++) {
cin >> yr[i];
y[i] = yr[i];
}

// Create AD configuration data object
ifail = 0;

// Calculate LU factorization

Integer           lfill = -1;
Integer           nnzc, npivm;
dtol = 0.0;
ifail  = 0;
ipivp,ipivq,istr,idiag,nnzc,npivm,iwork,liwork,ifail,1,1);

// Check value of npivm

if (npivm>0) {
cout << " Factorization is not complete" << endl;
} else {

//       Solve P L D U x = y

ifail = 0;
idiag,"C",y,x,ifail,1,1);

// Output results
cout.setf(ios::scientific,ios::floatfield);
cout.precision(4);
cout << "  Solution vector" << endl;
for (int i=0; i<n; ++i) {
cout.width(12);cout << nagad_a1w_get_value(x[i]) << "     ";
}

cout << "\n\n Derivatives calculated: First order adjoints\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives of solution X w.r.t RHS Y:\n";

// Setup evaluation of derivatives via adjoints
for (int i=0; i<n; i++) {
double inc = 1.0;
ifail = 0;

for (int j=0; j<n; j++) {
Integer k = i + j*n;
}
}
// Print derivatives
cout << endl;
NagError fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor,Nag_GeneralMatrix,Nag_NonUnitDiag,n,n,dxdy,n,
"       dx_i/dy_j",0,&fail);
}
// Remove computational data object and tape
ifail = 0;

delete [] a;
delete [] x;
delete [] y;
delete [] icol;
delete [] idiag;
delete [] ipivp;
delete [] ipivq;
delete [] irow;
delete [] istr;
delete [] iwork;
delete [] ar;
delete [] yr;
delete [] dxdy;

return exit_status;
}
```