[petsc-users] Index set with zero size

[Jed Brown]

On Thu, Nov 11, 2010 at 17:03, Tim Kroeger
<tim.kroeger at cevis.uni-bremen.de>wrote:

> One more question: Does this bux and fix also apply to a submatrix of an
> MPIAIJ matrix? That is, can I safely use MatMultAdd() having v2==v3 for such
> a matrix in 3.1.0-p4 or not?  (I'm having trouble with such a matrix now,
> but the error might be on my side.)


MPIAIJ implements MatGetSubMatrix, so it returns a new, efficient MatMPIAIJ
matrix.  This patch only affects matrix types that do not implement
MatGetSubMatrix, and thus fall back on creating a MatSubMatrix (which just
holds a reference to the original matrix and implements multiplication
through scatters).

So calling MatMultAdd using a matrix of any type other than MatSubMatrix is
unrelated to my patch.

Jed
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