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Yes it works,</div>
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but does not provide a correct solution and is stationary in time, I was just pointing this out. </div>
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I'll try to get as much as I can from the PetscFE object, PETSc provides already a lot of stuff, it cannot do everything.</div>
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Thanks for the support and time dedicated,</div>
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Matteo</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Da:</b> Mark Adams <mfadams@lbl.gov><br>
<b>Inviato:</b> giovedì 19 febbraio 2026 18:15<br>
<b>A:</b> Matteo Leone <matteo4.leone@mail.polimi.it><br>
<b>Cc:</b> PETSc users list <petsc-users@mcs.anl.gov><br>
<b>Oggetto:</b> Re: [petsc-users] Fw: DG methods in PETSc</font>
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<div dir="ltr">Just to avoid confusion with a convoluted thread, here is my response reposed:
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<div>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</div>
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<div>I see that the Riemann solver is set:</div>
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<div> PetscCall(PetscDSSetRiemannSolver(ds, 0, RiemannSolver_Advection));</div>
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<div>I would not recommend using DG because there are no tests for it. </div>
<div>There are tests for PetscDSSetRiemannSolver that you could clone and replace the FE/FV construction in those with DG:</div>
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<div>src/ts/tutorials/ex11.c: PetscCall(PetscDSSetRiemannSolver(prob, 0, user->model->physics->riemann));<br>
src/ts/tutorials/ex18.c: if (user->velocityDist == VEL_ZERO) PetscCall(PetscDSSetRiemannSolver(prob, 1, riemann_advection));<br>
src/ts/tutorials/ex18.c: else PetscCall(PetscDSSetRiemannSolver(prob, 1, riemann_coupled_advection));</div>
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<div>If you get this far, you might want to look at internal examples (not tests) and clone these DG constructors:</div>
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<div>src/dm/dt/fe/interface/fe.c: PetscFECreateBrokenElement - Create a discontinuous version of the input `PetscFE`<br>
src/dm/dt/fe/interface/fe.c:PetscErrorCode PetscFECreateBrokenElement(PetscFE cgfe, PetscFE *dgfe)<br>
src/dm/impls/plex/plexcreate.c: PetscCall(PetscFECreateBrokenElement(fe, &dgfe));<br>
src/dm/interface/dmcoordinates.c: PetscCall(PetscFECreateBrokenElement(feLinear, &dgfe));</div>
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<div>Sorry we do not have DG fully deployed yet.</div>
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<div>Good luck,</div>
<div>Mark</div>
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<div dir="ltr" class="x_gmail_attr">On Thu, Feb 19, 2026 at 12:14 PM Matteo Leone via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov">petsc-users@mcs.anl.gov</a>> wrote:<br>
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<div id="x_m_-7346522953463486077divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Matteo Leone <<a href="mailto:matteo4.leone@mail.polimi.it" target="_blank">matteo4.leone@mail.polimi.it</a>><br>
<b>Sent:</b> Thursday, February 19, 2026 3:36:44 PM<br>
<b>To:</b> Mark Adams <<a href="mailto:mfadams@lbl.gov" target="_blank">mfadams@lbl.gov</a>><br>
<b>Subject:</b> R: [petsc-users] DG methods in PETSc</font>
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Hello, I now have tested quite a bit the code, and I have some doubts.</div>
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Note I am quite new to PETSc.</div>
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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.</div>
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The Riemann solver is never called and also the solution is just static in time. </div>
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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). </div>
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(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).</div>
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There is also a small .py to handle the visualization (It was made by Claude code, but it just plots the results)</div>
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Hopefully we can go deep into this PETSc DG stuff.</div>
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Thanks in advace.</div>
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Matteo</div>
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<div id="x_m_-7346522953463486077x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>Da:</b> Mark Adams <<a href="mailto:mfadams@lbl.gov" target="_blank">mfadams@lbl.gov</a>><br>
<b>Inviato:</b> mercoledì 11 febbraio 2026 17:25<br>
<b>A:</b> Matteo Leone <<a href="mailto:matteo4.leone@mail.polimi.it" target="_blank">matteo4.leone@mail.polimi.it</a>>; PETSc users list <<a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a>><br>
<b>Oggetto:</b> Re: [petsc-users] DG methods in PETSc</font>
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<div dir="ltr">Great, and keep it on the list. Lots of people here to help!</div>
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<div dir="ltr">On Wed, Feb 11, 2026 at 9:46 AM Matteo Leone <<a href="mailto:matteo4.leone@mail.polimi.it" target="_blank">matteo4.leone@mail.polimi.it</a>> wrote:<br>
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Wow thank you so much! I was almost hopeless, I'll deep dive into it and I'll give you a feedback.</div>
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Matteo</div>
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<font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Mark Adams <<a href="mailto:mfadams@lbl.gov" target="_blank">mfadams@lbl.gov</a>><br>
<b>Sent:</b> Wednesday, February 11, 2026 3:38:30 PM<br>
<b>To:</b> Matteo Leone <<a href="mailto:matteo4.leone@mail.polimi.it" target="_blank">matteo4.leone@mail.polimi.it</a>><br>
<b>Cc:</b> <a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a> <<a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a>><br>
<b>Subject:</b> Re: [petsc-users] DG methods in PETSc</font>
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<div dir="ltr">DG (discontinuous Galerkin) is done with a "Broken" FE. Yikes I do not see a test.
<div>Here is a test but it is not well verified.</div>
<div>Mark</div>
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<div dir="ltr">On Tue, Feb 10, 2026 at 10:25 AM Matteo Leone via petsc-users <<a href="mailto:petsc-users@mcs.anl.gov" target="_blank">petsc-users@mcs.anl.gov</a>> wrote:<br>
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Hello, I already posted on Reddit but just to be sure I write even here.</div>
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First thanks for the job you do for PETSc, I have used it for several projects and is always nice.</div>
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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. </div>
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I was wondering if I am maybe missing something out or what.</div>
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For reference I use PETSc 3.24.3 by means of nix. </div>
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Thanks in advance, cheers.</div>
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Matteo</div>
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