Corbin,

Do you know if this problem is only present in 1d?



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On Mon, Apr 3, 2023, 18:36 Corbin Foucart <corbin.fouc...@gmail.com> wrote:

> Hello everyone,  I'm solving a 1D explicit DG-FEM problem and I've
> encountered behavior that I don't understand using MeshWorker: : mesh_loop.
> I'm using the MeshWorker: : assemble_own_interior_faces_both flag since I
> want to do work on each face
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> Hello everyone,
>
> I'm solving a 1D explicit DG-FEM problem and I've encountered behavior
> that I don't understand using MeshWorker::mesh_loop.
>
>    - I'm using the MeshWorker::assemble_own_interior_faces_both flag
>    since I want to do work on each face corresponding to the same cell 
> interior
>    - If the grid is created using typical GridGenerator calls, the order
>    is exactly as I'd expect: first, work is done on the cell, then the faces
>    (boundary or interior), followed by the next cell (further, all mass
>    matrices are the same)
>    - However, if I manually adapt the mesh by refining some cells, the
>    order seems to change; the face work is done without respect to the cell
>    interior last worked on
>
> I've attached a stripped-down program that illustrates this behavior on a
> toy mesh in 1D, as well as the output.
>
>    - Ultimately, my goal is to assemble an inverse mass matrix on each
>    cell, and apply it to a residual vector containing interior and face
>    contributions (which can be done element-wise since the elements are
>    FE_DGQ)
>    - I was attempting to store the inverse via CopyData and then apply it
>    in the copy worker.
>    - However, I'm finding that due to the order of execution, I can't
>    rely on the face work being done immediately after the cell work, and the
>    inverse mass matrix stored to CopyData is often from another cell than the
>    faces being worked on.
>    - I could do the assembly and application of the inverse mass matrices
>    separately, or store the inverse mass matrices in a map to the cell
>    iterators, but I'm curious why this ordering occurs.
>
> Am I misunderstanding how mesh_loop is supposed to work? Any guidance
> would be appreciated!
>
> Corbin
>
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