Hi Matt, Sorry, I should have been more clear. L and D are not lower triangular or anything, they are just matrices that are easy to invert in specific ways that are not compatible simultaneously. all the best --cjc ________________________________ From: Matthew Knepley <knepley@gmail.com> Sent: 30 April 2019 00:52:42 To: Cotter, Colin J Cc: firedrake Subject: Re: [firedrake] two splittings On Mon, Apr 29, 2019 at 4:30 PM Cotter, Colin J <colin.cotter@imperial.ac.uk<mailto:colin.cotter@imperial.ac.uk>> wrote: Dear Firedrakers, Greetings from Montreal. I'm thinking about a double splitting method to solve the system (M + D + L)u = f, which as a preconditioner works out as (M + D)^{-1}M(M + L)^{-1} r, where r is a residual. In the absence of a better idea, I'll implement this through a Python preconditioner. But is there a smarter way to do this? Isn;t this just SOR? Matt all the best --cjc _______________________________________________ firedrake mailing list firedrake@imperial.ac.uk<mailto:firedrake@imperial.ac.uk> https://mailman.ic.ac.uk/mailman/listinfo/firedrake -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener https://www.cse.buffalo.edu/~knepley/<http://www.cse.buffalo.edu/~knepley/>