[petsc-users] Guidance on GAMG preconditioning

[Mark Adams]

On Thu, Jun 4, 2015 at 12:29 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Thu, Jun 4, 2015 at 10:31 AM, Justin Chang <jychang48 at gmail.com> wrote:
>
>> Yeah I saw his recommendation and am trying it out. But I am not sure
>> what most of those parameters mean. For instance:
>>
>> 1) What does -pc_gamg_agg_nsmooths refer to?
>>
>
> This is always 1 (its the definition of smoothed aggregation). Mark allows
> 0 to support unsmoothed aggregation, which may be
> better for easy problems on extremely large machines.
>
>
>> 2) Does increase in the threshold of -pc_gamg_threshold translate to
>> making the coarsening faster?
>>
>
> Yes, I believe so (easy to check).
>

Other way around.
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