tut08-page01-example1.cc (flens/examples/tut08-page01-example1.cc)

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#include <cxxstd/iostream.h>

#include <flens/flens.cxx>

using namespace std;

using namespace flens;

typedef double   T;

int

main()

{

    typedef GbMatrix<BandStorage<T> >           Matrix;

    typedef DenseVector<Array<T> >              Vector;

    typedef Matrix::IndexType                   IndexType;

    const IndexType n = 4;

///

/// The first two indices define the dimensions, the two last ones the

/// the number of sub- and superdiagonals.

///

    Matrix         Ab(n, n, 2, 1);

    Vector         b(n), x(n);

    Ab.diag(-2) =  2, 3;

    Ab.diag(-1) = -6, 5, -4;

    Ab.diag( 0) =  4, 3,  5, -1;

    Ab.diag( 1) =  1, 2,  7;

    b = 20,

       -33,

       -43,

        49;

    cout << "Ab = " << Ab << endl;

    cout << "b  = " << b << endl;

    ///

    /// The function lower() creates a triangular banded matrix.

    /// We compute $x = A_{lower}^T b$.

    ///

    x = transpose(Ab.lower())*b;

    cout << "x = " << x << endl;

    ///

    /// And solve  $x = A_{lower}^T b$.

    ///

    blas::sv(Trans, Ab.lower(), x);

    cout << "b = " << x << endl;

    return 0;

}