[petsc-dev] PCFieldSplitSetFields() API change

Jed Brown jedbrown at mcs.anl.gov
Wed Jun 6 16:58:10 CDT 2012

On Fri, Mar 23, 2012 at 10:15 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> On Mar 23, 2012, at 6:22 PM, Jed Brown wrote:
> > But what does using B as 00 block actually mean? It seems to me that you
> pivot, producing P' P J where P J has B in the 00 location.
>    I am not arguing if it is pivoting or not. I'm arguing what the user
> interface should be.  Say I want D to be the 00 block then I just set that
> with PCFieldSplitSetFields() as the zeroth field. My point is that I am
> proposing a SINGLE interface for setting the blocks locations in all
> circumstances, while you are proposing having an additional interface for
> certain 00 configurations (pivoting) thus with your model you first call
> the PCFieldSplitSetFields() and then something else.

I just talked about this more with Dmitry.

It seems that we need to name both the row and column spaces of the
operator. Which begs the question: what is DM? Is it a distribution of the
state space (column space for a linear operator), a distribution of the
residual space (row space), or both? If both, we should make it possible to
select arbitrary pairs.
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