There's a numpy.abs but no numpy.matlib.abs. >> import numpy as N >> import numpy.matlib as M >> >> N.abs? Type: ufunc Base Class: <type 'numpy.ufunc'> String Form: <ufunc 'absolute'> Namespace: Interactive Docstring: y = absolute(x) takes |x| elementwise. >> M.abs? Object `M.abs` not found.