[petsc-dev] API changes in MatIS

Jed Brown jedbrown at mcs.anl.gov
Mon Jun 11 08:47:11 CDT 2012

The problem is that you can't factor the subdomain problem directly because
it is singular. So you either copy it into a bigger matrix (with Lagrange
multipliers) or extract a submatrix (by dropping vertices).

If I assemble a matrix with selected vertices, I can factor it and solve
the constrained problems without needing to refactor.

The case with no selected vertices could be a special case, and worked with
exactly like MatIS is now.
On Jun 11, 2012 8:35 AM, "Stefano Zampini" <stefano.zampini at gmail.com>

> I missed your answer...my e-mail client hid your last email.
>>> Do you mean assembling the matrix on preselected vertices during
>>> MatAssemblyBegin/End? Note that this will imply that standard
>>> Neumann-Neumann methods will not work (they need the unassembled matrix to
>>> solve for the local Schur complements).
>> I'm not too concerned about that since I consider the classic N-N and
>> original FETI methods to be rather special-purpose compared to the newer
>> generation. I would like to limit the number of copies of a matrix to
>> control peak memory usage.
> Duplicate vertices don't concur so much to memory usage as faces and edge
> nodes do, so why limit your matrix class? In principle the new class should
> handle _every_ nonoverlapping method, either belonging to the old or the
> new generation.
> --
> Stefano
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