[petsc-users] Advice Being Sought

[Barry Smith]

   Mark,

   Are you going to try this out?

    Thanks 

    Barry

On May 3, 2013, at 9:16 AM, David Scott <d.scott at ed.ac.uk> wrote:

> Barry,
> 
> On 23/04/2013 02:36, Barry Smith wrote:
>> 
>> On Apr 22, 2013, at 11:26 AM, David Scott <d.scott at ed.ac.uk> wrote:
>> 
>>> Thanks for the suggestion.
>>> 
>>> I had tried '-pc_type gamg -pc_gamg_agg_nsmooths 1' with an earlier version of the code without success. I have tried it again but I get NaN's after only 90 time steps whereas with block Jacobi it runs quite happily for 36,000 time steps and produces physically sensible results.
>> 
>>   David,
>> 
>>     We would be very interested in determining what is "going wrong" with the solver here since we hope to make it robust.  Would it be possible for you to use a MatView() and VecView() on the matrix and the right hand side with a binary viewer when it "goes bad" and send us the resulting file?
>> 
>>    Barry
>> 
>> We'd run the gamg solver on your matrix and track down what is happening.
>> 
>> 
> 
> I have inserted
>    call PetscViewerBinaryOpen(PETSC_COMM_WORLD, 'DifficultSystem', &
>      FILE_MODE_WRITE, viewer, ierr)
>    call KSPGetOperators(ksp, A, PETSC_NULL_OBJECT, &
>      PETSC_NULL_INTEGER, ierr)
>    call MatView(A, viewer, ierr)
>    call KSPGetRhs(ksp, b, ierr)
>    call VecView(b, viewer, ierr)
>    call PetscViewerDestroy(viewer, ierr)
> in my code after KSPSolve.
> 
> You may download the result for the 29th time step from
>  http://www2.epcc.ed.ac.uk/~dscott6/
> 
> I can generate data for other time steps if necessary.
> 
> David
> -- 
> Dr. D. M. Scott
> Applications Consultant
> Edinburgh Parallel Computing Centre
> Tel. 0131 650 5921
> 
> The University of Edinburgh is a charitable body, registered in
> Scotland, with registration number SC005336.