[firedrake] preconditioner for time-dependent Stokes

Dear all, I'd very much like to try the preconditioner in Mardal, Kent-Andre, and Ragnar Winther. "Uniform preconditioners for the time dependent Stokes problem." *Numerische Mathematik* 98.2 (2004): 305-327. This is an additive preconditioner that involves summing the result of two different preconditioning systems. What is the best path to trying this right now? Is it the new matrix-free stuff? cheers --cjc -- http://www.imperial.ac.uk/people/colin.cotter www.cambridge.org/9781107663916