Hi, It seems that <boost/numeric/ublas/matrix.hpp> includes <iostream>. I remember that it is better not to include <iostream> but something like <ostream> and <istream>, or even simply <iosfwd>. I'm wondering if this issue shall be corrected in the future version of ublas. Thanks, Peng #include <boost/numeric/ublas/matrix.hpp> int main () { std::cout << "Hello" << std::endl; }