[petsc-users] Implementing periodicity using DMPlex

[Shashwat Tiwari]

Hi,
I am writing a first order 2D solver for unstructured grids with periodic
boundaries using DMPlex. After generating the mesh, I use
"DMSetPeriodicity" function to set periodicity in both directions. After
which I partition the mesh (DMPlexDistribute), construct ghost cells
(DMPlexConstructGhostCells), create a section, and set some initial values
in the global vector. Then I use "VecGhostUpdateBegin" to start updating
the boundary ghost cell values, but, I get the following error in case I
use multiple processors:

[0]PETSC ERROR: Invalid argument
[0]PETSC ERROR: Vector is not ghosted
[0]PETSC ERROR: See https://www.mcs.anl.gov/petsc/documentation/faq.html
for trouble shooting.

if I run with a single process, there is no error but the values remain
empty (zero) and are not updated. Kindly let me know, if I am missing some
crucial step before I can update the ghost values in order to implement the
periodic bc, or if there is any other approach to achieve it. I am
attaching a small code to demonstrate the issue for your reference.

Regards,
Shashwat
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