[petsc-dev] Problematic Merge of FieldSplit

Dmitry Karpeev karpeev at mcs.anl.gov
Tue Jul 10 03:43:54 CDT 2012

I have a couple of questions about the usage DMGetSubDM() to define the
1) Should this be DMGetFieldSubDM(), since I can imagine other types of
subDMs (e.g., for a DD subdomain)?
In fact, I would advocate something like DMGetFieldSplitSubDM(), because
term "field" is getting abused and means
both an elementary building block with a split defined by DMGetSubDM()
composed of several such fields and the split itself.
2) Why not refer to the fields by string names?  A DM could advertise its
available fields via DMGetFieldNames() or similar,
with default field names such as "0", "1", etc.  DMGetFieldSplitSubDM()
would take a list of string constants from the list returned
by DMGetFieldNames().

This can be implemented independently of DMGetSubDM() to allow both designs
to evolve to the point where they can be merged.


On Tue, Jun 26, 2012 at 6:13 AM, Matthew Knepley <knepley at gmail.com> wrote:

> It turns out that 'hg rollback' during an 'hg rebase' does not do what I
> thought it did. I think
> everything is cleaned up with this push, but if you made FS changes in the
> past month, please
> check that it is doing what you want with prefixes, etc.
> Now, nested fieldsplits from the command line work, ala
> -ksp_type fgmres
> -pc_type fieldsplit -pc_fieldsplit_type additive
>   -pc_fieldsplit_0_fields 0,1
>     -fieldsplit_0_pc_type fieldsplit
>     -fieldsplit_0_pc_fieldsplit_type schur
> -fieldsplit_0_pc_fieldsplitschur_factorization_type full
>       -fieldsplit_0_fieldsplit_velocity_ksp_type preonly
>       -fieldsplit_0_fieldsplit_velocity_pc_type lu
>       -fieldsplit_0_fieldsplit_pressure_ksp_rtol 1e-10
>       -fieldsplit_0_fieldsplit_pressure_pc_type jacobi
>   -pc_fieldsplit_1_fields 2
>     -fieldsplit_temperature_ksp_type preonly
>     -fieldsplit_temperature_pc_type lu
> A split with only one field gets the field name, and otherwise a split
> number.
>     Matt
> --
> 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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