[petsc-dev] asm / gasm

[Boyce Griffith]

> On Jun 22, 2016, at 6:23 PM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> 
> 
>> On Wed, Jun 22, 2016 at 8:14 PM, Boyce Griffith <griffith at cims.nyu.edu> wrote:
>> 
>>> On Jun 22, 2016, at 2:06 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>> 
>>> 
>>>   I suggest focusing on asm. Having blocks that span multiple processes seems like over kill for a smoother ? (Major league overkill) in fact doesn't one want multiple blocks per process, ie. pretty small blocks.
>> 
>> And with lots of small blocks, remember to configure with --with-viewfromoptions=0. :-)
> 
> Yikes.  That is overkill right, unless you are worried about (users) accidentally using view and crashing the run with output.

No joke, Amneet found that PCASM with lots of small subdomains was spending a ton of time in view calls.

-- Boyce

> I guess we should have a flag or not iterate over the blocks in ASMView ...
>  
>> 
>> -- Boyce
>> 
>>> 
>>>   Barry
>>> 
>>>> On Jun 22, 2016, at 7:51 AM, Mark Adams <mfadams at lbl.gov> wrote:
>>>> 
>>>> I'm trying to get block smoothers to work for gamg.  We (Garth) tried this and got this error:
>>>> 
>>>> 
>>>> - Another option is use '-pc_gamg_use_agg_gasm true' and use '-mg_levels_pc_type gasm'.
>>>> 
>>>> 
>>>> Running in parallel, I get
>>>> 
>>>>     ** Max-trans not allowed because matrix is distributed
>>>> ----
>>>> 
>>>> First, what is the difference between asm and gasm?
>>>> 
>>>> Second, I need to fix this to get block smoothers. This used to work.  Did we lose the capability to have blocks that span processor subdomains?
>>>> 
>>>> gamg only aggregates across processor subdomains within one layer, so maybe I could use one layer of overlap in some way?
>>>> 
>>>> Thanks,
>>>> Mark
> 
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