Hi, I'm now testing dot product and using the following: import numpy as np, scipy.sparse as sp A = np.matrix(np.zeros((5,10))) B = np.zeros((10,1)) print (A*B).shape print np.dot(A,B).shape A = sp.csr_matrix(np.zeros((5,10))) B = sp.csr_matrix((10,1)) print (A*B).shape print np.dot(A,B).shape A = sp.csr_matrix(np.zeros((5,10))) B = np.zeros((10,1)) print (A*B).shape print np.dot(A,B).shape I got: (5, 1) (5, 1) (5, 1) (5, 1) (5, 1) (10, 1) Obviously, the last computation is not a dot product, but I got no warning at all. Is that the expected behavior ? By the way, I wrote a speed benchmark for dot product using the different flavors of sparse matrices and I wonder if it should go somewhere in documentation (in anycase, if anyone interested, I can post the benchmark program and result). Nicolas