Re: [Boost-Users] ublas matrix slice bug?

From: jhr.walter_at_[hidden]
Date: 2003-04-08 03:47:03

Hi Kresimir,

you wrote:

> >>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;
> >>}
> >
> > No. This one compiles with ICC 7.0 and fails with GCC 3.2.1.
>
> It also fails with como. As it should.

Thanks for checking that!

> This is the old problem of binding references to temporaries:
> parameters of `swap()' are *non-const* references, and they
> cannot be bound to temporaries returned by `row()'.
>
> It seems that `project()' raises its ugly head again :o(

Not sure about that. Maybe swap()'s signatures are inadequate for the view
classes. If I change matrix_row<>'s swap() member signatures from

        void swap (matrix_row &mr);
        friend void swap (matrix_row &mr1, matrix_row &mr2);

to

        void swap (matrix_row mr);
        friend void swap (matrix_row mr1, matrix_row mr2);

the following test program compiles on GCC 3.2.1 and Intel 7.0:

----------
#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));
    row(m,0).swap(row(m,2));
    swap(m.row(0), m.row(2));
    m.row(0).swap(m.row(2));

    matrix_row<matrix<double> > r1(m, 0), r2(m, 2);

    swap(r1, r2);
    r1.swap(r2);

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

----------

Interestingly enough, the same doesn't hold for 'const matrix_row &' instead
;-) I've already corrected swap() members for all view classes and intend to
upload my current version after some regression testing.

Thanks again,

Joerg