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 


> On Feb 14, 2018, at 5:50 AM, Lawrence Mitchell 
> <> 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

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