[petsc-users] Insufficient memory when using GMRES + Boomeramg

[Matthew Knepley]

On Wed, Mar 26, 2014 at 7:54 PM, TAY wee-beng <zonexo at gmail.com> wrote:

>  On 27/3/2014 12:14 AM, Matthew Knepley wrote:
>
>  On Wed, Mar 26, 2014 at 10:42 AM, TAY wee-beng <zonexo at gmail.com> wrote:
>
>>  On 26/3/2014 11:22 PM, Matthew Knepley wrote:
>>
>>  On Wed, Mar 26, 2014 at 9:59 AM, TAY wee-beng <zonexo at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I am running a CFD solver. The Poisson eqn was originally solved using
>>> HYPRE's geometric multigrid.
>>>
>>
>>  Is this on a structured grid?
>>
>>
>> Yes.
>>
>
>  Then you can replicate the Hypre structured MG with the PCMG, and it can
> be lighter memory than GAMG. You
> will need to code the problem in the style of SNES ex5, which is a Poisson
> for which geometric MG works from
> the command line.
>
>    Thanks,
>
>       Matt
>
> Hi Matt,
>
> First of all, is there an easier way out? Is it Boomeramg or GMRES which
> has a large memory requirement? Will changing e.g. GMRES to FGMRES or other
> ksp solvers solve the problem?
>

You could perhaps use a low-memory Krylov method, like BiCGStab. How big is
your Krylov space?


> Also, I switched from geometric multigrid (GMG) to Boomeramg because the
> latter is faster. If I use PCMG, am I going back to the GMG path, which was
> slower?
>

If multigrid is working correctly, it should take 10 iterates or so. I am
guessing something was wrong with the GMG, like coarse
BC.

  Thanks,

     Matt


> Thanks!
>
>
>
>>      Matt
>>
>>
>>> Recently, I tested it with Boomeramg as the preconditioner and GMRES as
>>> the ksp solver. There's a 20% increase in speed.
>>>
>>> However, when I increased the grid resolution, I got the out of memory
>>> error. Changing the solver back to HYPRE solved the problem.
>>>
>>> So does GMRES  + Boomeramg used more memory than other solvers? Are
>>> there alternatives?
>>>
>>> Thank you.
>>>
>>> --
>>> Yours sincerely,
>>>
>>> TAY wee-beng
>>>
>>>
>>
>>
>>  --
>> 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
>>
>>
>>
>
>
>  --
> 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
>
>
>


-- 
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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