[petsc-users] Questions about the PetscDSSetResidual and Nedelec element.

[Matthew Knepley]

On Tue, Apr 4, 2023 at 10:45 AM neil liu <liufield at gmail.com> wrote:

> Hello,
>
> I am learning this case,
> https://petsc.org/release/src/snes/tutorials/ex62.c.html
> . And try to make myself familiar with the FEM (PetscFE) there.
> Then I have several questions.
> 1)  PetscDSSetResidual
> <https://petsc.org/release/manualpages/DT/PetscDSSetResidual/>,
> For example, line 291,  PetscCall
> <https://petsc.org/release/manualpages/Sys/PetscCall/>(PetscDSSetResidual
> <https://petsc.org/release/manualpages/DT/PetscDSSetResidual/>(ds, 0,
> f0_quadratic_u, f1_u)), here, f0_quadratic_u and f1_u is function
> pointers. Where have the input parameter for these functions been
> calculated, e.g., u_x.
>

Line 291 sets callback functions. These functions are actually called in
the loop over the mesh which calculates the residual.
PETSc calculates u_x, given the PetscFE and the coefficients (and the
geometry).


> If I want to check the values of these parameters before line 291, how to
> print that ?
>

I output many thing with -dm_plex_print_fem 5, but I am not sure if I print
out the field jet. It would be easy to add.


> 2) Does PetscFE support Nedelec element? Will it be painful to add these
> modules myself ?
>

What kind? I think we support them, but have no tests. Take a look at our
support for Raviart-Thomas


https://gitlab.com/petsc/petsc/-/blob/main/src/dm/dt/dualspace/impls/lagrange/tutorials/ex1.c#L78

and see a use case here

  https://gitlab.com/petsc/petsc/-/blob/main/src/snes/tutorials/ex24.c

  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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