Hi all, I have a code in dolfinx that solves a system of PDEs in a rather complex geometry that I mesh using gmsh. The result is a vector field \mathbf m. I would now need to calculate some quantities for each cell of the mesh, for which I need to identify all the vertices that belong to them. Grap…

import dolfinx from mpi4py import MPI mesh = dolfinx.mesh.create_unit_square(MPI.COMM_WORLD, 2, 2, cell_type=dolfinx.mesh.CellType.quadrilateral) c2v = mesh.topology.connectivity(mesh.topology.dim, 0) print(c2v) 0: [0 1 2 3 ] 1: [1 4 3 5 ] 2: [2 3 6 7 ] 3: [3 5 7 8 ] [image]

Thanks a lot, @nate ! Could you please give me some more details on how to access these values and how to evaluate a fem.Function at them? Let’s say we have the mesh domain that I wrote in my previos post, and there I define element = ufl.VectorElement("CG", domain.ufl_cell(), 1, 3) V = fem.Functi…

Hi @dokken , thanks for your reply. I have looked into the post you linked and I think I know now how to access the vertices of a cell and operate with them. However, I don’t really understand the difference between vertices and dofs. I find that vertices = c_to_v.links(cell) and dofs = V0.dofmap.cel…

No, that is not always the case. A vertex is part of the mesh. Every cell has N number of vertices. A degree of freedom does not necessarily belong to a vertex (this is only the case for first order Lagrange elements). See for instance: DefElement

Hi again, @nate and @dokken . I realise now that I forgot to say that I actually need to access the nodes of a given cell in order, forming a closed loop (clockwise or anticlockwise is the same as long as I know which one it is). So in my first example, 0 -------- 1 -------- 4 | | …

I don’t understand why the way you are traversing the cell matters. You could always compute the orientation by computing the normal vector based on the geometry. See: FEniCS/dolfinx/blob/0ddbc45d4958a8350f5ef92e548037ec8b63d7d1/cpp/dolfinx/mesh/utils.h#L148-L149 ///…

Identifying cells and their vertices

mesh

dokken November 3, 2022, 2:12pm 4

See: Application of point forces, mapping vertex indices to corresponding DOFs - #2 by dokken

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Identifying cells and their vertices

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