Changing the Index Base

FLENS provides different ways to change the index base of a matrix. You can specify the index base when a matrix gets created. Or you can define special matrix types with their own default base.

Example Code

flens/examples/tut01-page02-example.cc

#include <flens/flens.cxx>

#include <iostream>

using namespace flens;

using namespace std;

int

main()

{

    typedef GeMatrix<FullStorage<double, ColMajor> >  GEMatrix;

    Underscore<GEMatrix::IndexType> _;

    GEMatrix A(_(0,3),_(-2,1));

    for (int i=A.firstRow(); i<=A.lastRow(); ++i) {

        for (int j=A.firstCol(); j<=A.lastCol(); ++j) {

            A(i,j) = 100*i+j;

        }

    }

    typedef IndexOptions<int, 0>                                 ZeroBased;

    typedef GeMatrix<FullStorage<double, ColMajor, ZeroBased> >  GEMatrixZB;

    GEMatrixZB  B(3,3);

    for (int i=B.firstRow(); i<=B.lastRow(); ++i) {

        for (int j=B.firstCol(); j<=B.lastCol(); ++j) {

            B(i,j) = 100*i+j;

        }

    }

    cout << "A(" << A.rows() << ", " << A.cols() << ") = " << A << endl;

    cout << "B(" << B.rows() << ", " << B.cols() << ") = " << B << endl;

    return 0;

}

Comments on Example Code

You can use the underscore range operator _(from, to) to set the index range of a matrix.

Note that in previous versions of FLENS the underscore object _ was already defined as a global variable. You now have to define it manually. This is because every matrix can now use different index types (usually int or long).

    typedef GeMatrix<FullStorage<double, ColMajor> >  GEMatrix;

    Underscore<GEMatrix::IndexType> _;

    GEMatrix A(_(0,3),_(-2,1));

Or define a GeMatrix type with a different index base. Here we set the default base to 0 such that both, row and col indices, start at zero.

    typedef IndexOptions<int, 0>                                 ZeroBased;

    typedef GeMatrix<FullStorage<double, ColMajor, ZeroBased> >  GEMatrixZB;

    GEMatrixZB  B(3,3);

Print matrix dimensions and content. Note that this time we use methods rows() and cols() which return range objects.

    cout << "A(" << A.rows() << ", " << A.cols() << ") = " << A << endl;

    cout << "B(" << B.rows() << ", " << B.cols() << ") = " << B << endl;

Compile and Run

$shell> cd flens/examples                                                       
$shell> g++ -Wall -std=c++11 -I../.. tut01-page02-example.cc                    
$shell> ./a.out                                                                 
A([0,3], [-2,1]) = 
           -2            -1             0             1 
           98            99           100           101 
          198           199           200           201 
          298           299           300           301 
B([0,2], [0,2]) = 
            0             1             2 
          100           101           102 
          200           201           202