[petsc-users] 2 level schur

[Luc Berger-Vergiat]

I hear you though that is not what petsc does.
When I name the fields as you suggest:

    -fieldsplit_0_fieldsplit_Field_0_fields 1
    -fieldsplit_0_fieldsplit_Field_1_fields 0

petsc ignores it and still call the fields

    -fieldsplit_0_fieldsplit_Field_2
    -fieldsplit_0_fieldsplit_Field_3

But the automatic naming scheme is not really the issue. It would just 
be nice to be able to switch the two fields.
I will try to change the order in which I pass the IS to the DM and see 
if I can go around the problem that way.

Best,
Luc

On 03/21/2014 12:13 PM, Matthew Knepley wrote:
> On Fri, Mar 21, 2014 at 9:37 AM, Luc Berger-Vergiat 
> <lb2653 at columbia.edu <mailto: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 <mailto: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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