One of the features I appreciate most about numpy is array broadcasting, probably because I hated having to use repmat() in my MATLAB days. With MATLAB, if you want to add the values in a vector to each column of a matrix, you have to replicate the vector to the same size as the matrix first, which is a colossal waste of memory (MATLAB does support something called lazy evaluation, but I'm not sure it applies to these sorts of expressions). In numpy you can simply add the vector to the matrix; however, the rules are a little tricky. There's an excellent FAQ on broadcasting here - how to specify which dimension should be matched between the two arrays, and when broadcasting is actually more inefficient.