[petsc-dev] Mark, what's the rational for keeping the Chebyshev tuning inside GAMG?

Mark Adams mfadams at lbl.gov
Wed Feb 25 11:13:15 CST 2015

> MatProjectDirichlet() would be useful here, too: it would allow the
> user to inject the right modifications to the near nullspace.

I'm not sure this is a good abstraction. These are coordinate
transformations.  Here you just want to know if the value should be zero
but in general you want a real transformation.

If the user rotates the local coordinate system to match the BC and zeros
out row(s) then there will be a dummy equation and you should, in theory,
rotate the null space, and the dumb MatProjectDirichlet do its job.  If the
user _then_ rotates the operator back (what you initially suggested I
think) then I don't think you need to do anything, now that I think about
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