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

Mark Adams mfadams at lbl.gov
Sun Jun 14 20:47:53 CDT 2015

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.

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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