[petsc-dev] automatic preconditioners for Stokes type problems?

[Matthew Knepley]

On Thu, Aug 5, 2010 at 9:45 AM, Mark F. Adams <mark.adams at columbia.edu>wrote:

> Jed brings up good points about false negatives, there are also false
> positives to worry about.  This is a bad idea, at least as a default solver.
>
>

I was not thinking about that at all. There would be no false positives
because the user would be required to
say "I have exactly this Stokes system, I am just too lazy to make my ISes,
please do it for me Magic PETSc".

   Matt


> That said, there is work on "adaptive" solvers like bootstrap AMG and using
> machine learning to formalize what it sounds like Barry is driving at.
>  Perhaps make a '-ksp_type black_box' solver type where you put any
> heuristics methods like this.  (this would require the KSP method to change
> the PC method which is ugly...)
>
> Mark
>
> On Aug 5, 2010, at 5:36 AM, Matthew Knepley wrote:
>
> On Thu, Aug 5, 2010 at 2:10 AM, Jed Brown <jed at 59a2.org> wrote:
>
>> On Thu, 5 Aug 2010 00:21:13 -0500, Matthew Knepley <knepley at gmail.com>
>> wrote:
>> > If someone tells us, "I have a Stokes problem", we could search for 0
>> > diagonals and create the partition for FS.
>>
>> I suppose this would work for some common cases, but there are lot of
>> discretizations and pressure-dependent constitutive relations/boundary
>> conditions that have nonzeros in the pressure block.  I think some slip
>> conditions can also produce zero or negative values in the momentum
>> block.
>>
>
> Do not disagree.
>
>
>> I'm not convinced that it's so much to ask people to provide an index
>> set, considering that FieldSplit is a somewhat advanced thing anyway
>> (based on sheer number of choices available, and (typical) sensitivity
>> to those choices).
>
>
> I guess the point here is somewhat like the point of DAs. It is a very
> limited
> thing, but something many people do. So we provide a way to most easily
> do the very limited thing.
>
> Not sure if this is useful enough, but it might be.
>
>    Matt
>
>
>>
>> Jed
>>
>
>
>
> --
> 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
>
>
>


-- 
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
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