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?

all the best

--cjc