[petsc-users] Implementing periodicity using DMPlex

[Jed Brown]

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Shashwat Tiwari <shaswat121994 at gmail.com> writes:

> Yeah I have use that too. I am getting zero values even in the Local Vector.

Corresponding to the ghost cells you created for that purpose, or otherwise?

> On Sat, 13 Jun 2020, 12:57 am , <jed at jedbrown.org> wrote:
>
>> You need DMGlobalToLocal.
>>
>> VecGhost is a different thing.
>>
>> On Jun 12, 2020 13:17, Shashwat Tiwari <shaswat121994 at gmail.com> wrote:
>>
>> 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
>>
>>
>>