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

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#include <cxxstd/iostream.h>

#include <flens/flens.cxx>

using namespace std;

using namespace flens;

int

main()

{

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

    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 $A = LQ$.  Note that the workspace gets created

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

///

    lapack::lqf(A, tau);

    //lapack::lqf(A, tau, work);

///

/// Solve $L u = b$.  Vector $b$ gets overwritten with $u$.

///

    const auto L = A.lower();

    blas::sv(NoTrans, L, b);

///

/// Explicitly setup $Q$.

///

    Q = A;

    lapack::orglq(Q, tau);

    //lapack::orglq(Q, tau, work);

    cout << "Q = " << Q << endl;

///

/// Compute $x = Q^T u$.

///

    DenseVector<Array<double> >  x;

    x = transpose(Q)*b;

    cout << "x = " << x << endl;

}