```/* F07FD_A1W_F C++ Header Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
* Mark 26.2, 2017.
*/

#include <nag.h>
#include <nagx04.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <iostream>
using namespace std;

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

cout << "F07FD_A1W_F C++ Header Example Program Results\n\n";
// Skip heading in data file
string mystr;
getline (cin, mystr);

Integer n;
cin >> n;

// Allocate arrays containing A and its factorized form, B
// and the solution X.
double            *ar;
if (!(a   = NAG_ALLOC(n*n, nagad_a1w_w_rtype)) ||
!(ar  = NAG_ALLOC(n*n, double))) {
cout << "Allocation failure\n";
exit_status = -1;
goto END;
}

// Read the lower triangular matrix A, register and copy
double dd;
for (int i = 0; i<n; ++i) {
for (int j = 0; j<=i; ++j) {
cin >> dd;
int k = i + j*n;
a[k].value = dd;
a[k].id = 0;
ax[k] = a[k];
}
}

// Create AD configuration data object
ifail = 0;

// Factorize the matrix A
ifail = 0;

// Print Factor
for (int i = 0; i<n; i++) {
for (int j = 0; j<=i; j++) {
int k = i + j*n;
}
}
cout << endl;
NagError  fail;
INIT_FAIL(fail);
x04cac(Nag_ColMajor,Nag_LowerMatrix,Nag_NonUnitDiag,n,n,ar,n,
"  Factor",0,&fail);

cout << "\n\n Derivatives calculated: First order adjoints\n";
cout << " Computational mode    : algorithmic\n";
cout << "\n Derivatives of diagonal of L w.r.t first column of A:\n";

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

Integer inc = 1.0;
int k = i + i*n;
ifail = 0;

for (int j=0; j<n; j++) {
ar[i+j*n] = dd;
}
}
// Print derivatives
cout << endl;
INIT_FAIL(fail);
x04cac(Nag_ColMajor,Nag_GeneralMatrix,Nag_NonUnitDiag,n,n,ar,n,
"  Derivatives dL(i,i)/dA(j,1)",0,&fail);

END:
// Remove computational data object and tape
ifail = 0;