[petsc-dev] ML via --download-ml

[Mark Adams]

FYI, ML has some different defaults (eg, its "threshold" is 0 and GAMG is
finite as I recall).  I have "verified" GAMG against ML a year or so ago,
but I had to set: -pc_gamg_threshold 0.
Mark

On Fri, Jun 12, 2015 at 7:38 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Fri, Jun 12, 2015 at 6:24 AM, Garth N. Wells <gnw20 at cam.ac.uk> wrote:
>
>> I've noticed very different performance with ML when I (a) link PETSc
>> to a Trilinos installation; or (b) use --download-ml. I observe
>>
>> - Case (a): solver behaves exactly as I would expect. Iteration counts
>> very close to GAMG iteration counts, minimal dependency on problem
>> size.
>>
>> - Case (b): iteration counts higher and substantial increase in
>> iteration count with problem size.
>>
>> I haven't debugged since I usually link to Trilinos, in which case
>> performance is as I expect.
>
>
> ML stopped being distributed independent of Trilinos a while ago, so we
> might not
> have upstream changes. This sounds like a difference of settings. The
> first step I think
> is to look at -ksp_view for both runs.
>
>   Thanks,
>
>      Matt
>
>
>> Garth
>>
>
>
>
> --
> 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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