On Thu, Jun 24, 2021 at 10:34 AM Abisheik Panneerselvam < [email protected]> wrote:

Hello,

Good Morning. My name is Abisheik Panneerselvam and I am presently working in Max-Planck Düsseldorf.

I am working on a FE software development project. The FE computation code is already written in Fortran (using Petsc for solving) few years ago. I am currently working on post-processing the results of the computation (nodal displacements, integration point displacements etc.). I am facing problems in getting the coordinates of vertices. I tried the following

call SNESGetDM(mechanical_snes,dm_local,ierr); CHKERRQ(ierr) !Gets the local DM from the SNES solve

call DMGetLocalVector(dm_local,x_local,ierr); CHKERRQ(ierr) !Gets the local vector from the DM

This functions successfully gets the coordinates of all the nodes. This works fine for linear elements as there are only nodes on cell vertices. But for higher order elements, the local vector (x_local) contains additional nodal points (I think its called ghost points in Petsc) on the edges. In this case how do I get the coordinates of only the cell vertices?

I tried the below code for getting the vertex coordinates but its giving random values.

call DMPlexGetDepthStratum(dm_local, 0, vStart, vEnd,ierr); CHKERRQ(ierr) !Get the vertices

call VecGetArrayF90(x_local, node_coords_local,ierr)

v_count=1

do v=vStart, vEnd-1

call DMPlexGetPointLocal(dm_local, v, x, y, ierr); CHKERRQ(ierr) !Get the position of the vertice in the local DM

d_count=1

do d=x,y-1

node_coords(d_count,v_count)=node_coords_local(d)

d_count=d_count+1

end do

v_count = v_count+1

end do

It will be really helpful if you could advise me on this.

Hi Abisheik, One question to start off. Are you using DMPlex to describe the grid? It sounded like your FEM code was in Fortran. If you are only using PETSc for solving the equations, it will not know the difference between unknowns on vertices and edges. Thanks, Matt

Best regards

Abisheik

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