[petsc-users] Problem with solving Poisson eqn for some cases

[TAY wee-beng]

On 17/3/2018 1:15 AM, Matthew Knepley wrote:
> On Fri, Mar 16, 2018 at 12:54 PM, TAY wee-beng <zonexo at gmail.com 
> <mailto:zonexo at gmail.com>> wrote:
>
>
>     On 15/3/2018 6:21 PM, Matthew Knepley wrote:
>>     On Thu, Mar 15, 2018 at 3:51 PM, TAY wee-beng <zonexo at gmail.com
>>     <mailto:zonexo at gmail.com>> wrote:
>>
>>         Hi,
>>
>>         I'm running a CFD code which solves the momentum and Poisson
>>         eqns.
>>
>>         Due to poor scaling with HYPRE at higher cpu no., I decided
>>         to try using PETSc with boomeramg and gamg.
>>
>>         I tested for some small cases and it work well. However, for
>>         the large problem which has poor scaling, it gives an error
>>         when I change my Poisson solver from pure HYPRE to PETSc with
>>         boomeramg and gamg.
>>
>>         The error is :
>>
>>         Caught signal number 11 SEGV: Segmentation Violation,
>>         probably memory access out of range
>>
>>         I tried using:
>>
>>         -poisson_ksp_type richardson -poisson_pc_type hypre
>>         -poisson_pc_type_hypre boomeramg
>>
>>         -poisson_ksp_type gmres -poisson_pc_type hypre
>>         -poisson_pc_type_hypre boomeramg
>>
>>         -poisson_pc_type gamg -poisson_pc_gamg_agg_nsmooths 1
>>
>>         but they all gave similar error.
>>
>>         So why is this so? How should I troubleshoot? I am now
>>         running a debug ver of PETSc to check the error msg.
>>
>>
>>     1) For anything like this, we would like to see a stack trace
>>     from the debugger or valgrind output.
>>
>>     2) We do have several Poisson examples. Does it fail for you on
>>     those?
>     Hi,
>
>     Can you recommend me some suitable egs? Esp in Fortran?
>
>
> Here is 2D Poisson
>
> https://bitbucket.org/petsc/petsc/src/4b6141395f14f0c7d1415a2ff0158eec75a27d63/src/snes/examples/tutorials/ex5f.F90?at=master&fileviewer=file-view-default
>
>>
>>     3) You can also try ML, which is the same type of MG as GAMG.
>>     (--download-ml).
>>
I have recompiled PETSc with ML. Is there an example command line 
options which I can use for ML?

Another question is generally speaking, is geometric multigrid (GMG) 
faster than algebraic?

I tested on a small problem and the time taken varies from 1.15min 
(HYPRE, geometric) to 3.25 (GAMG). BoomerAMG is 1.45min.

Besides HYPRE, is there any other GMG I can use?
>
>     My cluster can't connect to the internet. Where can I 1st download it?
>
>     Similarly, how can I find out the location of the ext software by
>     myself?
>
>
> The locations are all in the configure Python modules:
>
> https://bitbucket.org/petsc/petsc/src/4b6141395f14f0c7d1415a2ff0158eec75a27d63/config/BuildSystem/config/packages/ml.py?at=master&fileviewer=file-view-default
>
>   Thanks,
>
>     Matt
>
>>       Thanks,
>>
>>          Matt
>>
>>
>>         -- 
>>         Thank you very much.
>>
>>         Yours sincerely,
>>
>>         ================================================
>>         TAY Wee-Beng (Zheng Weiming) 郑伟明
>>         Personal research webpage:
>>         http://tayweebeng.wixsite.com/website
>>         <http://tayweebeng.wixsite.com/website>
>>         Youtube research showcase:
>>         https://www.youtube.com/channel/UC72ZHtvQNMpNs2uRTSToiLA
>>         <https://www.youtube.com/channel/UC72ZHtvQNMpNs2uRTSToiLA>
>>         linkedin: www.linkedin.com/in/tay-weebeng
>>         <http://www.linkedin.com/in/tay-weebeng>
>>         ================================================
>>
>>
>>
>>
>>     -- 
>>     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
>>
>>     https://www.cse.buffalo.edu/~knepley/
>>     <http://www.caam.rice.edu/%7Emk51/>
>
>
>
>
> -- 
> 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
>
> https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/%7Emk51/>

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