[petsc-users] 2 level schur

[Matthew Knepley]

On Fri, Mar 21, 2014 at 9:37 AM, Luc Berger-Vergiat <lb2653 at columbia.edu>wrote:

>  Is there a way to now what the new numbering is?
> I am assuming that in y example since there are two fields only the
> numbers associated with them are 0 and 1 hence I tried:
>
> -fieldsplit_0_fieldsplit_Field_2_fields 1
> -fieldsplit_0_fieldsplit_Field_3_fields 0
>
>
If its an inner fieldsplit, the numbering for options starts over again

  -fieldsplit_0_fieldsplit_Field_0_fields 1
  -fieldsplit_0_fieldsplit_Field_1_fields 0

  Thanks,

     Matt

>  which did not work. As mentioned earlier, the following does not work
> either:
>
> -fieldsplit_0_fieldsplit_Field_2_fields 3
> -fieldsplit_0_fieldsplit_Field_3_fields 2
>
> and without too much expectation I also passed the following
>
> -fieldsplit_0_fieldsplit_Field_2_fields Field_3
> -fieldsplit_0_fieldsplit_Field_3_fields Field_2
>
> to no avail.
>
> By the way I attached the output from -ksp_view in case I might be doing
> something wrong?
>
> Best,
> Luc
>
> On 03/20/2014 09:01 PM, Matthew Knepley wrote:
>
>  On Thu, Mar 20, 2014 at 6:20 PM, Luc Berger-Vergiat <lb2653 at columbia.edu>wrote:
>
>>  Hi all,
>> I am solving a four field problem using two Schur complements. Here are
>> the arguments that I usually pass to PETSc to do it:
>>
>> -ksp_type gmres -pc_type fieldsplit -pc_fieldsplit_type schur
>> -pc_fieldsplit_schur_factorization_type full
>> -pc_fieldsplit_schur_precondition selfp -pc_fieldsplit_0_fields 2,3
>> -pc_fieldsplit_1_fields 0,1 -fieldsplit_0_ksp_type preonly
>> -fieldsplit_0_pc_type fieldsplit -fieldsplit_0_pc_fieldsplit_type schur
>> -fieldsplit_0_pc_fieldsplit_schur_factorization_type full
>> -fieldsplit_0_pc_fieldsplit_schur_precondition selfp
>> -fieldsplit_0_fieldsplit_Field_2_fields 2
>> -fieldsplit_0_fieldsplit_Field_3_fields 3
>> -fieldsplit_0_fieldsplit_Field_2_ksp_type preonly
>> -fieldsplit_0_fieldsplit_Field_2_pc_type ilu
>> -fieldsplit_0_fieldsplit_Field_3_ksp_type preonly
>> -fieldsplit_0_fieldsplit_Field_3_pc_type jacobi -fieldsplit_1_ksp_type
>> preonly -fieldsplit_1_pc_type lu -malloc_log mlog -log_summary time.log
>>
>> One issue with this is that when I change
>> -fieldsplit_0_fieldsplit_Field_2_fields 2 to
>> -fieldsplit_0_fieldsplit_Field_2_fields 3 it is ineffective, as if PETSc
>> automatically assign IS 2 to Field 2 even though it is not what I want.
>> Is there a way to pass the arguments correctly so that PETSc goes about
>> switching the IS set of -fieldsplit_0_fieldsplit_Field_2 and
>> -fieldsplit_0_fieldsplit_Field_3?
>> This is crucial to me since I am using the selfp option and the matrix
>> associated to IS 3 is diagonal. By assigning the fields correctly I can get
>> an exact Schur preconditioner and hence very fast convergence. Right now my
>> convergence is not optimal because of this.
>>
>
>  I believe the inner Schur field statements should not be using the
> original numbering, but the inner numbering, after they have been reordered.
>
>     Matt
>
>
>> Thanks!
>>
>> Best,
>> Luc
>>
>
>
>
>  --
> 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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