ublas matrix slice bug?

From: Stephan Puchegger (puchs_at_[hidden])
Date: 2003-04-01 08:15:29

Dear ublas developers!

(I am using boost 1.30 & gcc 3.2)

the following program:

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>

int main () {
    using namespace boost::numeric::ublas;
    matrix<double> m (4, 4);
    for (unsigned int i = 0; i < m.size1 (); ++ i)
        for (unsigned int j = 0; j < m.size2 (); ++ j)
                m(i, j) = 1;

    std::cout << m << std::endl;

    // multiply a slice of the matrix with 2....
    project (m, slice (2, 1, m.size1()-2), slice (1, 0, m.size1()-2)) *= 2;

    // interesting result ... the slice has been multiplied with 4
    std::cout << m << std::endl;
}

gives the following output:

[4,4]((1,1,1,1),(1,1,1,1),(1,1,1,1),(1,1,1,1))
[4,4]((1,1,1,1),(1,1,1,1),(1,4,1,1),(1,4,1,1))

Why is the slice multiplied with 4 and not with 2?? Do I make some
fundamental mistake? Everything works fine if I am using a
matrix_vector_slice.

My second (stupid?) question is the following: Is it intentional, that it
is not possible to compile:

#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>

int main () {
    using namespace boost::numeric::ublas;
    matrix<double> m (4, 4);
    for (unsigned int i = 0; i < m.size1 (); ++ i)
        for (unsigned int j = 0; j < m.size2 (); ++ j)
                m(i, j) = 4*i+j;

    std::cout << m << std::endl;

    swap(row(m,0), row(m,2));

    std::cout << m << std::endl;
}

whereas

matrix_row<matrix<double> > l(m, 0);
matrix_row<matrix<double> > r(m, 2);

swap(l, r); /* swap the rows */

works fine. MTL has support for a similar syntax:

swap(rows(m)[0], rows(m)[2]);

best regards and thanks for your help!

        Stephan