Ok, in a hurry, I think I've make some mistakes, but I've tracked down the problem to this:
    ublas::matrix<double> A(2, 2), B(2, 2), C(2, 2);
    // initialize A and B ...
    C = prod(A, ublas::matrix<double>(prod(B, A))); // C = A*B*A  this works
    C = prod(A, prod(B, A)); // C = A*B*A  this doesn't work
Somebody knows why do I have to use a temporary for this expression, or am I doing something wrong again?
Daniele


On 10/16/07, Daniele <asloxx@gmail.com> wrote:
Hi all,
I'm rather new to boost::ublas, and I was trying to use it to do some simple math in a C++ program (no big speed requirement here, yet).
I have some code like the following (see below for a complete test):

        ublas::slice sl(0, 6, 3);
        // matlab equiv (I think): P([1 4], [1 4]) = A*P([1 4], [1 4])*A' + Q
A and Q are 2x2, P is 6x6
        project(P, sl, sl) = prod(A, prod(project(P, sl, sl), trans(A))) + Q;

but I get a static assertion triggered. This is the error gcc gives me (gcc 4.1.2, gentoo linux):

/usr/include/boost/numeric/ublas/matrix_expression.hpp: In function 'typename boost::numeric::ublas::matrix_matrix_binary_traits<typename E1::value_type, E1, typename E2::value_type, E2>::result_type boost::numeric::ublas::prod(const boost::numeric::ublas::matrix_expression<E>&, const boost::numeric::ublas::matrix_expression<E2>&) [with E1 = boost::numeric::ublas::matrix<double, boost::numeric::ublas::basic_row_major<unsigned int, int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > >, E2 = boost::numeric::ublas::matrix_matrix_binary<boost::numeric::ublas::matrix_slice<boost::numeric::ublas::matrix<double, boost::numeric::ublas::basic_row_major<unsigned int, int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > > >, boost::numeric::ublas::matrix_unary2<boost::numeric::ublas::matrix<double, boost::numeric::ublas::basic_row_major<unsigned int, int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > >, boost::numeric::ublas::scalar_identity<double> >, boost::numeric::ublas::matrix_matrix_prod<double, double, double> >]':
ublas_test.cpp:27:   instantiated from here
/usr/include/boost/numeric/ublas/matrix_expression.hpp:4637: error: invalid application of 'sizeof' to incomplete type 'boost::STATIC_ASSERTION_FAILURE<false>'

and this is the assertion in matrix_expression.hpp:4647:

BOOST_STATIC_ASSERT (E1::complexity == 0 && E2::complexity == 0)

Any clue on what am I doing wrong?


Thanks,
Daniele

P.S. this is the complete test program that I was trying to compile:
#include <iostream>
// boost ublas headers
#include <boost/numeric/ublas/vector.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/io.hpp>
#include <boost/numeric/ublas/vector_proxy.hpp>
#include <boost/numeric/ublas/matrix_proxy.hpp>

using namespace std;
namespace ublas = boost::numeric::ublas;


int main(void)
{
    using ublas::project;
    ublas::matrix<double> P(4, 4);
    ublas::matrix<double> A(2, 2);
    ublas::matrix<double> Q(2, 2);

    // initialize P, A, Q ...

    ublas::slice sl(0, 6, 3);
    // matlab equiv (I think: P([1 4], [1 4]) = A*P([1 4], [1 4])*A' + Q
    project(P, sl, sl) = prod(A, prod(project(P, sl, sl), trans(A))) + Q;

    cout << P << endl;
}