Since I did not get an answer on a related question, I am trying to state it different. It seems as if the "[]" access is not supported for const objects. Is there a reason for this, or is it a bug? Example: ========================================================== #include <boost/numeric/ublas/config.hpp> #include <boost/numeric/ublas/vector.hpp> #include <boost/numeric/ublas/matrix.hpp> using namespace boost::numeric::ublas; void foo(vector<double>& v, const vector<double>& a) { } int main(int argc, char* argv[]) { vector<double> v (3); const matrix<double> m(3,3); foo(v, m[0]); } ========================================================== my compiler does not compile this. This is a problem when I get the matrix as a "const matrix<>& " parameter via the argument list. Regards, Roland