[petsc-dev] Lies in PCFieldSplit

[Barry Smith]

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.
>