Dear all, Thank you for your responses. I've taken some time to think about your comments and I have some more questions: Paul: Are you suggesting to represent the moments on the 2*M grid and not project it back onto the original space? I am assuming this means that the moments would be in the space of polynomials of order 2*N. Am I understanding correctly? Aleks: You talk about truncating to polyn. order < lx1. Would this have the same effect as projecting onto the original space? Also, is the "cut_off_filter" subroutine the correct way to implement this? Thanks, Juan Diego