[petsc-dev] asm / gasm

[Mark Adams]

On Wed, Jun 22, 2016 at 5:13 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Jun 22, 2016 at 5:51 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?
>>
>
> ASM is very simple Additive Schwarz which can have multiple blocks per
> process, but cannot have blocks spanning
> processes. GASM was meant to generalize this, but Dmitry wrote it and (to
> my knowledge) the support situation is
> uncertain. Maybe Barry know better.
>
>
>> 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?
>>
>
> Did we ever have it?
>

I thought so but it's been a long time. The code did work at one point but
now I (Garth) gets this error.

Does anyone know about this error? I don't find it with 'git grep Max-trans'

Thanks,
Mark


>
>
>> gamg only aggregates across processor subdomains within one layer, so
>> maybe I could use one layer of overlap in some way?
>>
>
> ASM can do arbitrary overlap.
>
>   Matt
>
>
>> Thanks,
>> Mark
>>
>>
>
>
> --
> 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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