Hi, I have the following c++ function: void multi_state_kf::correction(const vector<double>& obs, const matrix<double>& dev) { compute_gain(dev); vector<double> temp = (m*obs-newX*m); x=newX+prod(temp,K); matrix<double> T=identity_matrix<double>(3,3)-K*m; matrix<double> temp2=prod(T,newP); matrix<double> temp3=prod(K,dev); P=prod(temp2,trans(T))+prod(temp3,trans(K)); } The syntax is completely hacked together as this is my first attempt at using boost's uBLAS, but it got rid of most of my errors except this one: \boost\numeric\ublas\functional.hpp(190): error C2440: '=' : cannot convert from 'const boost::numeric::ublas::matrix_binary_scalar2::value_type' to 'double' (...) The odd (for me) part is that even when I remove all boost function calls from the function the compile error still shows up and it points me to a line in the functional.hpp file. So 1. Does anyone know what could be causing this compile error? 2. What's a better way of writing this function? Thanks in advance, Nick