please keep this on the list. On Thu, Feb 19, 2026 at 9:36 AM Matteo Leone <[email protected]> wrote:

Hello, I now have tested quite a bit the code, and I have some doubts. Note I am quite new to PETSc.

I have modified a bit your code to test it and I tried to print from the functions to check if they were actually called with negative results. The Riemann solver is never called and also the solution is just static in time.

This was a work in progress, but it does run: ./ex9 -dm_plex_box_faces 8,8 -dm_plex_dim 2 -dm_plex_simplex 0 -order 1 -ts_max_steps 10 -ts_monitor -velocity 1.0,0.5 I see that the Riemann solver is set: PetscCall(PetscDSSetRiemannSolver(ds, 0, RiemannSolver_Advection)); I would not recommend using DG because there are no tests for it. There are tests for PetscDSSetRiemannSolver that you could clone and replace the FE/FV construction in those with DG: src/ts/tutorials/ex11.c: PetscCall(PetscDSSetRiemannSolver(prob, 0, user->model->physics->riemann)); src/ts/tutorials/ex18.c: if (user->velocityDist == VEL_ZERO) PetscCall(PetscDSSetRiemannSolver(prob, 1, riemann_advection)); src/ts/tutorials/ex18.c: else PetscCall(PetscDSSetRiemannSolver(prob, 1, riemann_coupled_advection)); If you get this far, you might want to look at internal examples (not tests) and clone these DG constructors: src/dm/dt/fe/interface/fe.c: PetscFECreateBrokenElement - Create a discontinuous version of the input `PetscFE` src/dm/dt/fe/interface/fe.c:PetscErrorCode PetscFECreateBrokenElement(PetscFE cgfe, PetscFE *dgfe) src/dm/impls/plex/plexcreate.c: PetscCall(PetscFECreateBrokenElement(fe, &dgfe)); src/dm/interface/dmcoordinates.c: PetscCall(PetscFECreateBrokenElement(feLinear, &dgfe)); Sorry we do not have DG fully deployed yet. Good luck, Mark

I share the code. It's a bit modified and no more c but c++ (I do not know to write the csv file fom c, in case is a dealbreaker I'll try to give a look on how to do it). (For reference I use PETSc 3.24.4 by means of nix, the nix flake is in the shared docs if you are used to it lmk).

There is also a small .py to handle the visualization (It was made by Claude code, but it just plots the results) Hopefully we can go deep into this PETSc DG stuff.

Thanks in advace. Matteo

------------------------------ *Da:* Mark Adams <[email protected]> *Inviato:* mercoledì 11 febbraio 2026 17:25 *A:* Matteo Leone <[email protected]>; PETSc users list < [email protected]> *Oggetto:* Re: [petsc-users] DG methods in PETSc

Great, and keep it on the list. Lots of people here to help!

On Wed, Feb 11, 2026 at 9:46 AM Matteo Leone <[email protected]> wrote:

Wow thank you so much! I was almost hopeless, I'll deep dive into it and I'll give you a feedback.

Matteo

------------------------------ *From:* Mark Adams <[email protected]> *Sent:* Wednesday, February 11, 2026 3:38:30 PM *To:* Matteo Leone <[email protected]> *Cc:* [email protected] <[email protected]> *Subject:* Re: [petsc-users] DG methods in PETSc

DG (discontinuous Galerkin) is done with a "Broken" FE. Yikes I do not see a test. Here is a test but it is not well verified. Mark

On Tue, Feb 10, 2026 at 10:25 AM Matteo Leone via petsc-users < [email protected]> wrote:

Hello, I already posted on Reddit but just to be sure I write even here.

First thanks for the job you do for PETSc, I have used it for several projects and is always nice.

I am writing cause I am getting mad trying to implement DG solver in PETSc, the target is the Euler equations, however I am failing even with just the simplest transport equation (u/t + u/x = 0). I was wondering if I am missing somenthing. I tried with the DSSetReimannSolver and DualSpaces, and more, but I keep failing, I tried also with LLMs, but seems like there is no DG code with PETSc on the web, however I see many papers that do it.

I was wondering if I am maybe missing something out or what.

For reference I use PETSc 3.24.3 by means of nix.

Thanks in advance, cheers.

Matteo