On Fri, May 5, 2023 at 10:55 AM Vilmer Dahlberg via petsc-users <petsc-users@mcs.anl.gov> wrote:

Hi.


I'm trying to read a mesh of higher element order, in this example a mesh consisting of 10-node tetrahedral elements, from gmsh, into PETSC. But It looks like the mesh is not properly being loaded and converted into a DMPlex. gmsh tells me it has generated a mesh with 7087 nodes, but when I view my dm object it tells me it has 1081 0-cells. This is the printout I get


Hi Vilmer,

Plex makes a distinction between topological entities, like vertices, edges and cells, and the function spaces used to represent fields, like velocity or coordinates. When formats use "nodes", they mix the two concepts together.

You see that if you add the number of vertices and edges, you get 7087, since for P2 there is a "node" on every edge. Is anything else wrong?

  Thanks,

     Matt
 

...


Info    : Done meshing order 2 (Wall 0.0169823s, CPU 0.016662s)

Info    : 7087 nodes 5838 elements

...

DM Object: DM_0x84000000_0 1 MPI process
  type: plex
DM_0x84000000_0 in 3 dimensions:
  Number of 0-cells per rank: 1081
  Number of 1-cells per rank: 6006
  Number of 2-cells per rank: 9104
  Number of 3-cells per rank: 4178
Labels:
  celltype: 4 strata with value/size (0 (1081), 6 (4178), 3 (9104), 1 (6006))
  depth: 4 strata with value/size (0 (1081), 1 (6006), 2 (9104), 3 (4178))
  Cell Sets: 1 strata with value/size (2 (4178))
  Face Sets: 6 strata with value/size (12 (190), 21 (242), 20 (242), 11 (192), 22 (242), 10 (188))
Field P2:
  adjacency FEM
...


To replicate the error try generating a mesh according to


https://gmsh.info/doc/texinfo/gmsh.html#t5


setting the element order to 2, and then loading the mesh using


DMPlexCreateGmshFromFile


I don't have any issues when i set the element order to 1.


Thanks in advance,

Vilmer



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What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
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