On Dec 2, 2012, at 11:13 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> 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.
Sarcasm on: yupp, hence diag (which most people would interpret as short for
diagonal) is a great name: sarcasm off.
What about just using A11?
Barry
>
> >
> > 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.
>
