[petsc-users] (Fast?) assembly of upper triangle and MatZeroRows

[Jed Brown]

On Mon, Aug 8, 2011 at 17:16, Barry Smith <bsmith at mcs.anl.gov> wrote:

> Add a KSP/SNES./TSSetDirichlet(ksp,snes,ts,IS listofnodes,Vec
> valuesfornodes)?
>

This might be worthwhile. It needs a new Mat primitive which zeros the rows
and columns while also "remembering" the column values that it zeroed (as
another assembled matrix). I think it's best to apply the transformation
immediately after residuals are calculated so that norms are correct (not in
KSP at all). Matrix values are not available at this time so the Dirichlet
equations may not be scaled correctly for GMG. We have to be careful that
the residual evaluation passed to MatMFFD has the Dirichlet projection
inside it.
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