[petsc-dev] API changes in MatIS

[Jed Brown]

Isn't PtAP still the right operation, you just have a particular
implementation that takes advantage of structure?

I know you can also assemble B A^{-1} B^T, which is the same thing, and
maybe we should provide a generic op for that.
On May 11, 2012 1:17 PM, "Stefano Zampini" <stefano.zampini at gmail.com>
wrote:

>
> 2012/5/11 Jed Brown <jedbrown at mcs.anl.gov>
>
>> I don't like this idea of the matrix type determining the algorithm, I'd
>> rather choose the algorithm.
>>
>
> This is note the case in my BDDC: it is the algorithm that drives the type
> of matrix to be built.
>
>
>> Can we decouple it by building the prolongation operator P whose columns
>> are harmonic extension of the coarse nodes? Then the coarse operator looks
>> like P^T A P just like multigrid (for which we have a matop) instead of
>> looking like a Schur complement.
>>
> I already have it. Each process has its local part, splitted in the
> matrices pcbddc->coarse_phi_B (local interface nodes) and  (optionally)
> pcbddc->coarse_phi_D (local dirichlet nodes). You can see that I used them
> to check the correctness of the coarse local part in the code (see line
> 1702 of bddc.c). I build the local part of coarse matrix , but I don't use
> the expensive PtAP operation. Instead, I evaluate it by exploiting
> properties of the saddle point problem they come from.
>
>
>
>
>>  On May 10, 2012 2:42 PM, "Stefano Zampini" <stefano.zampini at gmail.com>
>> wrote:
>>
>>>
>>> This is to do recursive BDDC or what?
>>>>
>>>>
>>> Yes. When creating the BDDC coarse matrix, now the code has three 3
>>> options
>>>
>>> A) coarse matrix is a MATIS -> multilevel BDDC
>>> B) coarse matrix is SEQAIJ -> one level BDDC with only one proc (or all)
>>> solving directly the coarse problem
>>> C) coarse matrix is MPIAIJ -> one level  BDDC with a parallel direct
>>> solve
>>>
>>> I think that PCREDUNDANT can do the job in both cases of options B if
>>> the matrix would be parallel.
>>>
>>
>
>
> --
> Stefano
>
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