[petsc-dev] asm / gasm

[Boyce Griffith]

> On Jun 22, 2016, at 7:34 PM, Boyce Griffith <griffith at cims.nyu.edu> wrote:
> 
> 
> 
> On Jun 22, 2016, at 6:23 PM, Mark Adams <mfadams at lbl.gov <mailto:mfadams at lbl.gov>> wrote:
> 
>> 
>> 
>> On Wed, Jun 22, 2016 at 8:14 PM, Boyce Griffith <griffith at cims.nyu.edu <mailto:griffith at cims.nyu.edu>> wrote:
>> 
>>> On Jun 22, 2016, at 2:06 PM, Barry Smith <bsmith at mcs.anl.gov <mailto: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.

(And, of course, Barry fixed it by adding this configure flag --- thanks Barry!)

Note that it does not matter whether you use view or not.

-- Boyce

> 
> -- 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 <mailto: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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