[petsc-users] Question about DMLocalToLocal for DM_BOUNDARY_GHOSTED conditions

[Matthew Knepley]

On Fri, May 22, 2020 at 4:34 PM Lucas Banting <bantingl at myumanitoba.ca>
wrote:

> Hello,
>
> I am converting a serial code to parallel in fortran with petsc. I am
> using the DMDA to manage communication of the information that used to be
> in old two-dimensional fortran arrays.
>
> I noticed when using DMLocalToLocalBegin/End, not all the ghost values in
> the array at the DM_BOUNDARY_GHOSTED area is updated. Is this expected
> behaviour?
>

I believe so. GHOSTED is user managed space. We do not touch it.


> I read through this thread:
> https://lists.mcs.anl.gov/mailman/htdig/petsc-users/2016-May/029252.html
> and saw someone had a similar question, but the answer was not clear to me.
>
> If this is expected behaviour, how should I instead update these values in
> my arrays? I was using DM_BOUNDARY_GHOSTED as I needed the extra ghost
> cells for some subroutines, but I do not need them in my matrix from
> DMCreateMatrix.
>

You fill them in the local vector.

  Thanks,

      Matt


> I am using Petsc 3.12.4 and open MPI 3.1.4.
>
> Thanks,
>
> Lucas Banting
>


-- 
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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