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

Tobin Isaac tisaac at ices.utexas.edu
Wed Feb 25 11:19:25 CST 2015

On Wed, Feb 25, 2015 at 12:13:15PM -0500, Mark Adams wrote:
> >
> >
> >
> > 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
> it.

I see your point.  Any users with local coordinate rotations for
Dirichlet conditions can probably provide their own near nullspace.
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