NAG Library Manual, Mark 28.7
Interfaces:  FL   CL   CPP   AD
```/* nag::ad::g02ab Passive Example Program.
*/

#include <dco.hpp>
#include <iostream>

std::stringstream filecontent("4 \
2.0   -1.0    0.0    0.0 \
-1.0    2.0   -1.0    0.0 \
0.0   -1.0    2.0   -1.0 \
0.0    0.0   -1.0    2.0 \
100.0   20.0   20.0   20.0");

// Function which calls NAG AD routines.
// Computes the Nearest Correlation Matrix X for an input matrix G.
template <typename T>
void func(std::vector<T> &g, std::vector<T> &w, std::vector<T> &x);

int main()
{
std::cout << " nag::ad::g02ab Passive Example Program Results\n";

Integer n;
filecontent >> n;

// Input Matrix G, whose NCM we want to compute
std::vector<double> gv(n * n);
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
filecontent >> gv[i + j * n];
}
}

// The square roots of the diagonal elements of W
std::vector<double> wv(n);
for (int i = 0; i < n; i++)
{
filecontent >> wv[i];
}

// Output NCM X
std::vector<double> xv(n * n);

// Call the NAG AD Lib functions
func(gv, wv, xv);

std::cout.setf(std::ios::scientific, std::ios::floatfield);
std::cout.precision(12);
std::cout << "\n Nearest Correlation Matrix:\n\n";
for (int i = 0; i < n; i++)
{
for (int j = 0; j < n; j++)
{
std::cout.width(20);
std::cout << xv[i + j * n];
}
std::cout << std::endl;
}

return 0;
}

// Function which calls NAG AD routines.
template <typename T>
void func(std::vector<T> &g, std::vector<T> &w, std::vector<T> &x)
{
Integer n   = sqrt(g.size());
Integer pdg = n;
Integer pdx = n;

// Set up method parameters
T       errtol = 0.0, alpha = 0.02;
Integer maxits = 0;
Integer maxit  = 0;
// Output variables
Integer iter, feval;
T       nrmgrd;
// Set a copy of g, since it will be modified by the example
std::vector<T> g_tmp = g;
// Create AD configuration data object
Integer           ifail = 0;