[petsc-users] Fwd: Inquiry about the dual space (PetscFECreateTabulation_Basic)

[Matthew Knepley]

On Fri, Apr 21, 2023 at 10:02 AM neil liu <liufield at gmail.com> wrote:

> Hello, Petsc group,
>
> I am learning the FE structure in Petsc by running case
> https://petsc.org/main/src/snes/tutorials/ex12.c.html with -run_type test
> -bc_type dirichlet -dm_plex_interpolate 0 -petscspace_degree 1
> -show_initial -dm_plex_print_fem 1
>

-dm_plex_print_fem 5 will print much more


> When I check the subroutine PetscFECreateTabulation_Basic, I can not
> understand some parameters there.
>
> For the following lines in the file (
> https://petsc.org/release//src/dm/dt/fe/impls/basic/febasic.c.html#PETSCFEBASIC
> )
>
> 135:   PetscCall <https://petsc.org/release//manualpages/Sys/PetscCall/>(PetscDualSpaceGetDimension <https://petsc.org/release//manualpages/DUALSPACE/PetscDualSpaceGetDimension/>(fem->dualSpace, &pdim));136:   PetscCall <https://petsc.org/release//manualpages/Sys/PetscCall/>(PetscFEGetNumComponents <https://petsc.org/release//manualpages/FE/PetscFEGetNumComponents/>(fem, &Nc));
>
> Here, Nc = 2, pdim =6. I am running a scalar case with degree of 1,
>
> I expect Nc = 1 and pdim =3. Could you please explain this? In addition,
>
> Sure. I am guessing that you are looking at the tabulation for the
coordinate space. Here you are in 2 dimensions, so the
coordinate space has Nc = 2. For multicomponent spaces, we currently do not
represent it as a tensor product over the
scalar space, so we see 6 basis vectors.

  Thanks,

     Matt

> Thanks,
>
> Xiaodong
>
>
>
>

-- 
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/ <http://www.cse.buffalo.edu/~knepley/>
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