[petsc-users] GlobalToLocal between DM and SubDM

[Matthew Knepley]

On Tue, Apr 30, 2019 at 1:20 PM Josh L via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Hi,
>
> I have a DM that that has 2 sections:
>
> section_0 has 2 dofs: u, v
> section_1 has 1 dofs: p
>
> and a SubDM created by DMCreateSubDM. SubDM only has section_1.
>
> There are a global vector created with DM, and a local vector created with
> SubDM
>
> Can I do GlobalToLocal between this 2 vectors?
>

No, the global and local vector have to have the same DM.

If yes, which DM should I use when calling GlobalToLocal.
>
> Basically, I want
> a global vec: [u1, v1, p1 u2, v2, p2, u3, v3, p3......]
> to
> local vec: [all dof p that belongs to this processor]
>

You will have to do it in two steps, either,

  1) Extract p in a subDM, and then do G2L on that

or

  2) Do G2L on the full DM, and then extract p from the local vec

1) sounds better to me, but I do not know what your code is doing.

  Thanks,

    Matt


>
> Thanks,
> Yu-Sheng
>
>
>
>
>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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