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

[Jed Brown]

On Mon, Aug 8, 2011 at 17:31, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 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 spoke too soon. If you apply the transformation while evaluating residuals
and during assembly, there is no need to have this after-the-fact
modification.

Is there a reason this information should not be held by the DM? In Dohp, I
use explicit projections into homogeneous and inhomogeneous spaces. Both are
needed, so it's not clear to me that this can cleanly be placed in SNES or
KSP without the weird semantics (modification of force vector or matrix, or
having MatMult tell us that we didn't solve the equations.

The concept of Dirichlet values (with homogeneous and inhomogeneous spaces)
could be pushed all the way down into Mat and Vec (some of which I did for
Dohp, in order to use VecGhost).
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