[petsc-users] Distribution of DMPlex for FEM

[Morten Nobel-Jørgensen]

Hi Matthew

Thanks for your answer and your fix. It works :)))

Kind regards,
Morten


Fra: Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>>
Dato: Thursday 14 July 2016 at 00:03
Til: Morten Nobel-Joergensen <mono at dtu.dk<mailto:mono at dtu.dk>>
Cc: "petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>" <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>>
Emne: Re: [petsc-users] Distribution of DMPlex for FEM

On Wed, Jul 13, 2016 at 3:57 AM, Morten Nobel-Jørgensen <mono at dtu.dk<mailto:mono at dtu.dk>> wrote:
I’m having problems distributing a simple FEM model using DMPlex. For test case I use 1x1x2 hex box elements (/cells) with 12 vertices. Each vertex has one DOF.
When I distribute the system to two processors, each get a single element and the local vector has the size 8 (one DOF for each vertex of a hex box) as expected.

My problem is that when I manually assemble the global stiffness matrix (a 12x12 matrix) it seems like my ghost values are ignored. I’m sure that I’m missing something obvious but cannot see what it is.

In the attached example, I’m assembling the global stiffness matrix using a simple local stiffness matrix of ones. This makes it very easy to see if the matrix is assembled correctly. If I run it on one process, then global stiffness matrix consists of 0’s, 1’s and 2’s and its trace is 16.0. But if I run it distributed on on two, then it consists only of 0's and 1’s and its trace is 12.0.

I hope that somebody can spot my mistake and help me in the right direction :)

This is my fault, and Stefano Zampini had already tried to tell me this was broken. I normally use DMPlexMatSetClosure(), which handles global indices correctly.
I have fixed this in the branch

  knepley/fix-plex-l2g

which is also merged to 'next'. I am attaching a version of your sample where all objects are freed correctly. Let me know if that works for you.

  Thanks,

     Matt

Kind regards,
Morten



--
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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20160714/c3d49f51/attachment.html>