Re: [petsc-dev] Bad scaling of GAMG in FieldSplit

[Mark Adams]

>
>
>>
>>> -pc_gamg_threshold[] <thresh,default=0> - Before aggregating the graph
>>> GAMG will remove small values from the graph on each level
>>> -pc_gamg_threshold_scale <scale,default=1> - Scaling of threshold on
>>> each coarser grid if not specified
>>>
>>
>> Nope.  Totally different things.
>>
>
> Well, you could use _threshold to do more aggressive coarsening, but not
> for thinning out
> the interpolation. There are some simple filters we might be able to use
> (Luke Olson talked
> about it today), but Mark is the expert.
>
>
I think they (and Luke?) are talking about methods that explicitly truncate
the support of the coarse grid functions. So they truncate the functions
and not the coarsening graph. GAMG does only the latter.