[petsc-users] Possible to recover ILU(k) from hypre/pilut?

Matthew Knepley knepley at gmail.com
Thu Nov 16 06:53:02 CST 2017


On Wed, Nov 15, 2017 at 10:57 PM, Mark Lohry <mlohry at gmail.com> wrote:

> What are the limitations of ILU in parallel you're referring to? Does
> Schwarz+local ILU typically fare better?
>


Anecdotally, the sweet spot for ILU(k) k > 0 is extremely small. For
smaller problems, sparse direct is so good its
hard to win with ILU(k) since you do at least a few iterates. For larger
problems, ILU(k) runs out of gas or memory
fairly fast, and its better to find a method tailored to the problem.

   Matt


> On Nov 15, 2017 10:50 PM, "Smith, Barry F." <bsmith at mcs.anl.gov> wrote:
>
>>
>>
>> > On Nov 15, 2017, at 9:40 PM, Jed Brown <jed at jedbrown.org> wrote:
>> >
>> > "Smith, Barry F." <bsmith at mcs.anl.gov> writes:
>> >
>> >>> On Nov 15, 2017, at 6:38 AM, Mark Lohry <mlohry at gmail.com> wrote:
>> >>>
>> >>> I've found ILU(0) or (1) to be working well for my problem, but the
>> petsc implementation is serial only. Running with -pc_type hypre
>> -pc_hypre_type pilut with default settings has considerably worse
>> convergence. I've tried using -pc_hypre_pilut_factorrowsize (number of
>> actual elements in row) to trick it into doing ILU(0), to no effect.
>> >>>
>> >>> Is there any way to recover classical ILU(k) from pilut?
>> >>>
>> >>> Hypre's docs state pilut is no longer supported, and Euclid should be
>> used for anything moving forward. pc_hypre_boomeramg has options for Euclid
>> smoothers. Any hope of a pc_hypre_type euclid?
>> >>
>> >>  Not unless someone outside the PETSc team decides to put it back in.
>> >
>> > PETSc used to have a Euclid interface.  My recollection is that Barry
>> > removed it because users were finding too many bugs in Euclid and
>> > upstream wasn't fixing them.  A contributed revival of the interface
>> > won't fix the upstream problem.
>>
>>    The hypre team now claims they care about Euclid. But given the
>> limitations of ILU in parallel I can't imagine anyone cares all that much.
>>
>>
>>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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