tut05-page02-example2.cc (flens/examples/tut05-page02-example2.cc)

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#include <cxxstd/iostream.h>

#define USE_CXXLAPACK

#include <flens/flens.cxx>

///

/// We use our high-level interface that we defined before.

///

#include "tut05-mylapack-version1.h"

using namespace flens;

using namespace std;

typedef double   T;

int

main()

{

    typedef GeMatrix<FullStorage<T> >           Matrix;

    typedef DenseVector<Array<T> >              Vector;

    typedef Matrix::IndexType                   IndexType;

    typedef DenseVector<Array<IndexType> >      IndexVector;

    const IndexType n = 4;

///

/// We define an underscore object to ease the creation of matrix/vector views.

///

    Underscore<IndexType>  _;

    Matrix         A(n,n);

    Vector         b(n);

    IndexVector    piv(n);

    A =  2,   3,  -1,   0,

        -6,  -5,   0,   2,

         2,  -5,   6,  -6,

         4,   6,   2,  -3.1;

    b = 20,

       -33,

       -43,

        49;

    cerr << "A = " << A << endl;

    cerr << "b = " << b << endl;

    IndexType info = mylapack::trf(A, piv);

    if (info==0) {

///

///     Passing `b(_(1,n))` as last argument to `trs` will cause a compile-time

///     error.  This is because the vector view `b(_(1,n))` is a temporary

///     object but `trs` expects a lvalue reference.

///

        mylapack::trs(NoTrans, A, piv, b(_(1,n)));

//

//      This would work (but it might be inconvenient):

//

//      auto b_ = b(_(1,n));

//      mylapack::trs(NoTrans, A, piv, b_);

//

        cerr << "x = " << b << endl;

    } else {

        cerr << "A is numerically singular." << endl;

    }

}