[petsc-dev] LU for MPIAIJ

[Barry Smith]

On Jan 7, 2013, at 8:15 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> 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.

   I can teach you how to use etags or you can teach me how to use PERL :-)

>  
> 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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>