[petsc-dev] Lies in PCFieldSplit

[Jed Brown]

On Sun, Dec 2, 2012 at 9:09 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> >> block diagonal part of A11 actually means A11, correct?  Otherwise what
> blocks????
>

Yeah, DIAG just meens to use the diagonal block (A11) directly, rather than
to build some approximation to the Schur complement.


> >
> > Processor diagonal. This is not ASM where what we select is
> > automatically process diagonal.
>
>    I don't see this at all. It seems to me we actually use A11 to form the
> preconditioner, of course if we use bjacobi as the preconditioner then it
> becomes the diagonal blocks of A11, but if we use, for example LU then we
> are using all of A11 in forming the preconditioner of S.
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