[petsc-users] FIELDSPLIT fields

[Fande Kong]

On Wed, Sep 5, 2018 at 9:54 AM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>   2 should belong to one of the subdomains, either one is fine.
>
>    Barry
>
>
> > On Sep 5, 2018, at 10:46 AM, Rossi, Simone <srossi at email.unc.edu> wrote:
> >
> > I’m trying to setup GASM, but I’m probably misunderstanding something.
> >
> > If I have this mesh
> >
> > 0 —— 1 —— 2 —— 3 —— 4
> > subdomain 1  |   subdomain 2
> >
>

You may need to make a decision which subdomain ``2" belongs to. Most
people just let the shared node go to the lower MPI rank. If so, in this
example, ``2" belongs to the subdomain one.

iis1 = {0, 1, 2}
ois  = {0, 1, 2, 3}

iis2 = {3, 4}
ois2 = {2, 3, 4}

You consider seriously to use GASM, I would suggest to partition  your
problem (using ``hierach") in such a way that multi-rank subdomain is
actually connected, otherwise you may end up having a deficient
performance.


Thanks,

Fande,




> > I create an interior (no overlap) and an outer (with overlap) IS for
> both subdomains.
> >
> > In my naive understanding
> >
> > iis1  = {0, 1}
> > ois1 = {0, 1, 2}
> >
> > and
> >
> > iis2  = {3, 4}
> > ois2 = {2, 3, 4}
> >
> > but then the node at the interface (node 2) does not belong to any
> interior IS. Should node 2 belong to both interior IS? Or should it belong
> only to one of the domains?
> >
> > Thanks,
> > Simone
> >
> >
> > On Aug 15, 2018, at 22:11, Griffith, Boyce Eugene <boyceg at email.unc.edu>
> wrote:
> >
> >>
> >>
> >>> On Aug 15, 2018, at 10:07 PM, Smith, Barry F. <bsmith at mcs.anl.gov>
> wrote:
> >>>
> >>>
> >>> Yes you can have "overlapping fields" with FIELDSPLIT but I don't
> think you can use FIELDSPLIT for your case. You seem to have a geometric
> decomposition into regions. ASM and GASM are intended for such
> decompositions. Fieldsplit is for multiple fields that each live across the
> entire domain.
> >>
> >> Basically there is one field the lives on the entire domain, and
> another field that lives only on a subdomain.
> >>
> >> Perhaps we could do GASM for the geometric split and FIELDSPLIT within
> the subdomain with the two fields.
> >>
> >>> Barry
> >>>
> >>>
> >>>> On Aug 15, 2018, at 7:42 PM, Griffith, Boyce Eugene <
> boyceg at email.unc.edu> wrote:
> >>>>
> >>>> Is it permissible to have overlapping fields in FIELDSPLIT? We are
> specifically thinking about how to handle DOFs living on the interface
> between two regions.
> >>>>
> >>>> Thanks!
> >>>>
> >>>> — Boyce
> >>>
> >>
> >
>
>
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