I am trying to figure out a way of doing the following (initialize a lower-triangular matrix P with 0's and fill the last row with 1's) using iterators: int n = 10; boost::numeric::ublas::triangular_matrixP(n, n); P = boost::numeric::ublas::zero_matrix<double>(n,n); for (unsigned col = 0; col < n; ++col) P(n, col) = 1.0; I want to try and use std::fill, so something like std::fill(P.begin1(), P.end() - (adjust pointer to not include the last row), 0.0); std::fill(P.begin2(), P.end2(), 1.0); I can't seem to find any examples though on how to use iterators for Boost lower triangular matrices. I know how to do this using STL vector, that's easy, but I'm not sure how to adjust the iterator pointer in this case. Thanks in advance for your help. Cheers, Max