[petsc-dev] LU for MPIAIJ

Jed Brown jedbrown at mcs.anl.gov
Mon Jan 7 20:15:26 CST 2013

On Mon, Jan 7, 2013 at 8:12 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

> On Jan 7, 2013, at 8:05 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:
> > It's sort of awkward to deal with PCREDUNDANT for coarse grids, and I
> have yet to see any evidence that it's better than gathering to rank 0,
> solving sequentially, and scattering the result. What about implementing LU
> for MPIAIJ to do the latter algorithm? Then we could trivially make it
> smart enough to skip the gather when Mark uses it on the coarse grid of
> GAMG (where the entire system is already on rank 0). In additon to being
> simpler for the user to interact with, this would fix a lot of fighting
> between the PCMG and its children.
>    I thought PCREDUNDANT had this ability? What about adding it?

That wouldn't be redundant at all, so if we put it there, we'd have to at
least rename it.

> Have an option that cause PCREDUNDANT to only collect a single copy of the
> matrix from rank 0 to r-1 and in your case r is 1.  I hate the idea of
> having another separate place with similar stuff to PCREDUNDANT.  You could
> then implement LU for MPIAIJ using this variant of PCREDUNDANT, that is a
> call to PCREDUNDANT stuff with the right options.
>    Barry
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