sycrs-cg.cc (flens/examples/sycrs-cg.cc)

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#include <cxxstd/cmath.h>

#include <cxxstd/iostream.h>

#include <flens/flens.cxx>

#include <flens/examples/cg.h>

using namespace flens;

using namespace std;

int

main()

{

    const int n = 5;

///

/// Let the diagonal of A have values of `2` and the off-diagonal `-1`.

///

    SyCoordMatrix<CoordStorage<double> >    A(n, Upper);

    for (int i=1; i<=n; ++i) {

        A(i,i) += 2;

        if (i<n) {

            A(i,i+1) -= 1;

        }

    }

///

/// Compress A and stor it in B

///

    SyCRSMatrix<CRS<double> >   B = A;

///

/// Vector `z` is the control solution.

///

    DenseVector<Array<double> > x(n), z(n), b(n);

    z = 1;

    b = B*z;

///

/// Solve $Bx=b$

///

    cg(B, b, x);

    cout << "x = " << x << endl;

///

/// Get the infinity norm of the error

///

    x -= z;

    cout << "max abs error = " << abs(x(blas::iamax(x))) << std::endl;

}