I think this should be simple, but I'm drawing a blank I have 2 2d matrixes Matrix A has indexes (i, symbol) Matrix B has indexes (state, symbol) I combined them into a 3d matrix: C = A[:,newaxis,:] + B[newaxis,:,:] where C has indexes (i, state, symbol) That works fine. Now suppose I want to omit B (for debug), like: C = A[:,newaxis,:] In other words, all I want is to add a dimension into A and force it to broadcast along that axis. How do I do that?