NAG Library Manual, Mark 29
```/* F11BD_P0W_F C++ Header Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
* Mark 29.0, 2023.
*/

#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 << "F11BD_P0W_F C++ Header Example Program Results\n\n";
// Skip heading in data file
string mystr;
getline(cin, mystr);

Integer n, m;
double  alpha;
cin >> n;
cin >> m;
cin >> alpha;

// Allocate arrays containing A and its factorized form, B
// and the solution X.
double *b = 0, *x = 0, *work = 0;
Integer lwork = 2 * m * n + 1000;

b    = new double[n];
x    = new double[n];
work = new double[lwork];

double bb, b1, a, c;

b1 = 12.0;
a  = 1.0;
c  = 1.0;
bb = b1 - 2.0;

ifail = 0;
for (int i = 0; i < n; ++i)
{
b[i] = b1 * (i + 1);
x[i] = 3.0;
}
b[n - 1] = b[n - 1] - (n + 1);

b[0] = b[0] + (b1 - 1.0) * alpha;
for (int i = 1; i < n - 1; ++i)
{
b[i] = b[i] + b1 * alpha;
}
b[n - 1] = b[n - 1] + (b1 - 1.0) * alpha;

// Initialize rthe solver
Integer iterm = 2, maxitn = 800, monit = 0, lwreq = lwork;
double  sigmax = 0.0, anorm;
double  tol    = 1.0e-10;
ifail          = 0;
anorm, sigmax, monit, lwreq, work, lwork, ifail);

// Reverse communication call of solver
Integer irevcm = 0;
double  wgt[1];

while (irevcm != 4)
{
ifail = 0;
if (irevcm != 4)
{
ifail = -1;
if (irevcm == -1)
{
//  b = A^Tx
b[0] = bb * x[0] + a * x[1];
for (int i = 1; i < n - 1; ++i)
{
b[i] = c * x[i - 1] + bb * x[i] + a * x[i + 1];
}
b[n - 1] = c * x[n - 2] + bb * x[n - 1];
}
if (irevcm == 1)
{
// b = Ax
b[0] = bb * x[0] + c * x[1];
for (int i = 1; i < n - 1; ++i)
{
b[i] = a * x[i - 1] + bb * x[i] + c * x[i + 1];
}
b[n - 1] = a * x[n - 2] + bb * x[n - 1];
}
if (irevcm == 2)
{
for (int i = 0; i < n; ++i)
{
b[i] = x[i] / bb;
}
}
}
}

cout.setf(ios::scientific, ios::floatfield);
cout.precision(2);

cout << "  Solution vector   Residual vector\n";
for (int i = 0; i < n; ++i)
{
cout.width(12);
cout << x[i] << "     ";
cout.width(13);
cout << b[i] << endl;
}

delete[] b;
delete[] x;
delete[] work;

return exit_status;
}
```