在 2022年6月16日，23:22，Matthew Knepley <knepley@gmail.com> 写道：



On Thu, Jun 16, 2022 at 11:11 AM Zongze Yang <yangzongze@gmail.com> wrote:

Hi, if I load a `gmsh` file with second-order elements, the coordinates will be stored in a DG-P2 space. After obtaining the coordinates of a cell, how can I map the coordinates to vertex and edge? 

By default, they are stored as P2, not DG.

I checked the coordinates vector, and found the dogs only defined on cell other than vertex and edge, so I said they are stored as DG.

Then the function DMPlexVecGetClosure seems return the coordinates in lex order.

Some code in reading gmsh file reads that

1756:     if (isSimplex) continuity = PETSC_FALSE; /* XXX FIXME Requires DMPlexSetClosurePermutationLexicographic() */

1758:     GmshCreateFE(comm, NULL, isSimplex, continuity, nodeType, dim, coordDim, order, &fe)

The continuity is set to false for simplex.

Thanks,

Zongze

You can ask for the coordinates of a vertex or an edge directly using

  https://petsc.org/main/docs/manualpages/DMPLEX/DMPlexPointLocalRead/

by giving the vertex or edge point. You can get all the coordinates on a cell, in the closure order, using

  https://petsc.org/main/docs/manualpages/DMPLEX/DMPlexVecGetClosure/

  Thanks,

     Matt

 

Below is some code load the gmsh file, I want to know the relation between `cl` and `cell_coords`.

```

import firedrake as fd
import numpy as np

# Load gmsh file (2rd)
plex = fd.mesh._from_gmsh('test-fd-load-p2-rect.msh')

cs, ce = plex.getHeightStratum(0)

cdm = plex.getCoordinateDM()
csec = dm.getCoordinateSection()
coords_gvec = dm.getCoordinates()

for i in range(cs, ce):
    cell_coords = cdm.getVecClosure(csec, coords_gvec, i)
    print(f'coordinates for cell {i} :\n{cell_coords.reshape([-1, 3])}')
    cl = dm.getTransitiveClosure(i)
    print('closure:', cl)
    break

```

Best wishes,

Zongze

--

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

https://www.cse.buffalo.edu/~knepley/