Lawrence, You analysis is correct; I don't know what I was thinking twenty+ years ago.
I think a fix could be to have an option that just creates a separate set of post smoothers and gives them a a different suffix. I'll try to do it on a branch and you can then follow the branch and make sure what I do works for you. I will call the branch barry/feature-mg-post-smooth Barry > On Feb 14, 2018, at 5:50 AM, Lawrence Mitchell > <lawrence.mitch...@imperial.ac.uk> wrote: > > Dear petsc-dev, > > I'd like to try out doing SOR-like smoothing for a problem with MG > where on the pre-smooth I run forwards, and on the post-smooth backwards. > > I can do this by setting up the PC and then spinning over the up and > down smoothers separately. I wonder if it would be possible to extend > the setup to allow it to be done from options. > > I had a look, but I got very lost in where/how the setup of the up > smoother separate from the down smoother works. It seems to be > triggered on whether you select a different number of smoothing steps > up and down, but I don't necessarily want that. > > I think I just want to select a different options prefix in > PCMGGetSmootherUp, but I can't obviously see how to ensure that's > called appropriately. > > Cheers, > > Lawrence