> R-B has crappy cache performance since you alternately pull data but ignore > half of it.
Understood. > Why not just use the GMG in PETSc? Its very flexible, scalable, > and efficient. I tried to use Petsc's implementation of multigrid, cf thread "V-cycle multigrid with matrix shells". My concern is performance. I'd like the whole procedure to use matrix shells, or "matrix-free" matrices, because my stencil can have up to 21 off-diagonal terms. Petsc 3.1 did not allow this functionality. I do not know what Petsc 3.2 has to offer in that regard. I have a working multi-grid method that uses the low functionality of Petsc. I would obviously prefer if I could use something more advanced. Cheers, Sylvain
