lapack-ormqr.cc (flens/examples/lapack-ormqr.cc)

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#include <cxxstd/iostream.h>

#include <flens/flens.cxx>

using namespace std;

using namespace flens;

typedef double   T;

int

main()

{

    GeMatrix<FullStorage<double> >     A(4,4);

    DenseVector<Array<double> >        b(4);

    DenseVector<Array<double> >        tau;

    //DenseVector<Array<double> >      work;

    A =  2,   3,  -1,   0,

        -6,  -5,   0,   2,

         2,  -5,   6,  -6,

         4,   6,   2,  -3;

    b = 20,

       -33,

       -43,

        49;

    cout << "A = " << A << endl;

    cout << "b = " << b << endl;

///

/// Compute the factorization $A = QR$.  Note that the workspace gets created

/// implicitly and temporarily.  So you might not want to do this inside a loop.

///

    lapack::qrf(A, tau);

    //lapack::qrf(A, tau, work);

///

/// Compute $\tilde{b} = Q^H b$. Vector $b$ gets overwritten with $\tilde{b}$.

///

    lapack::ormqr(Left, Trans, A, tau, b);

    //lapack::ormqr(Left, Trans, A, tau, b, work);

///

/// Solve $R x = \tilde{b}$.  Vector $b$ gets overwritten with $x$.

///

    blas::sv(NoTrans, A.upper(), b);

    cout << "x = " << b << endl;

}