Fix multigrid agglomeration

[bigfooted]

Proposed Changes

Give a brief overview of your contribution here in a few sentences.

Implement multigrid agglomeration according to Nishikawa and Diskin.

• euler walls are working correctly.

• mpi seems to be working (can be improved)

• OMP seems to be working (can be improved)

• multigrid does not crash anymore

• I am submitting my contribution to the develop branch.

• My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).

• My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).

• I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.

• I have added a test case that demonstrates my contribution, if necessary.

• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.

[pcarruscag]

I can help you with the OMP stuff, just point me to a simple case with issues.
What you're doing here doesn't work because CFL_fine is a thread-local variable, so only the master thread will have a value here.

[bigfooted]

Thank, pedro, I am still (a bit) lost here.

[bigfooted]

Hmmm I reverted this again, but this specific fix seems to solve the 'regular' thread sanitizer tests'. The AD thread sanitizer tests are still failing though.

In general, to fix commented‑out code, either fully reinstate it as active code (if it represents the intended behavior) or remove it altogether, possibly replacing it with a concise explanatory comment if some of its intent is important for understanding.

Here, the multigrid CFL is currently set to a fixed value 1.0, and the previously more complex logic to read CFL values in a SU2_OMP_MASTER block is commented out. Since the active code clearly uses the fixed value and there is no guarantee that the old code is still correct, the lowest‑risk fix is to remove the commented‑out code completely, while retaining the surrounding synchronization comments which explain the barriers. Concretely, in SU2_CFD/src/integration/CMultiGridIntegration.cpp, around lines 495–505, delete the lines starting with // passivedouble CFL_fine_passive = 0.0; through // END_SU2_OMP_MASTER. No new methods, imports, or definitions are needed; we are only cleaning up dead commented‑out code.

In general, to fix commented-out code issues you either (a) remove the dead code permanently if it is no longer needed, or (b) reinstate it as active code (possibly refactored into a function), or (c) convert it into clearly non-executable documentation (e.g., in a Doxygen block or as pseudo-code with markers). Here, the simplest way to fix the issue without changing existing functionality is to remove the block of commented-out code that was implementing a more complex CFL computation, because the current implementation intentionally uses a fixed CFL_coarse_new = 1.0.

Concretely, in SU2_CFD/src/integration/CMultiGridIntegration.cpp, in the multigrid loop around lines 495–507, delete the commented-out declarations of CFL_fine_passive and CFL_coarse_current_passive, the commented SU2_OMP_MASTER block, and the associated explanatory comment about the implicit barrier that specifically references these commented variables. Keep the surrounding comments about synchronization that still apply to the remaining code. No new methods, imports, or definitions are required; we are just removing unused, commented-out code.

[bigfooted]

@pcarruscag ok, it is definitely this CFL_coarse_new that is giving issues, I put it to constant and the thread sanitizer tests are passing now - no more race conditions.