Have you tried to create your arrays with the numpy.zeros functions rather than the scipy.zeros functions? I can imagine that something may get confused here. Maybe some version mismatch or what not. Mark From: Ryan Krauss <ryanlists <at> gmail.com> Subject: Re: problem with dot for complex matrices<http://news.gmane.org/find-root.php?message_id=%3cCAAroWSa4ZgEdhb4%3dyq%5fuv...> Newsgroups: gmane.comp.python.scientific.user<http://news.gmane.org/gmane.comp.python.scientific.user> Date: 2012-03-27 19:56:14 GMT (1 day and 18 minutes ago) The matrices are initially created by these lines: matout=scipy.zeros((n,n),dtype=complex128)#+0j colout=scipy.zeros((n,1),dtype=complex128)#+0j