Comments NSF (Entropy-Var) Gradients

[DanielDoehring]

Extending parts of #2527 to 2D, 3D.

Supposed to be merged after #2517, until then labeled as draft

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.76%. Comparing base (45823ed) to head (8818065).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2528   +/-   ##
=======================================
  Coverage   96.76%   96.76%           
=======================================
  Files         512      512           
  Lines       42391    42391           
=======================================
  Hits        41016    41016           
  Misses       1375     1375           

Flag	Coverage Δ
unittests	96.76% <ø> (ø)

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[andrewwinters5000]

I think these changes are confusing and/or misleading. It makes it seem that we need the gradients of either rho or w1. But these are not needed in any of the flux computations. They do get computed and passed around, but they are never modified or used.

[andrewwinters5000]

I am still not a fan of this. I my eyes we should have a separate set of variables of size nvars_grad to avoid the computation of unnecessary gradients like d_rho or d_w1. This commented section of code was intended to reflect such a desire. So changing it to include the unnecessary gradient values goes against its spirit.

[DanielDoehring]

I agree, this would be nice - I gave it a quick look this morning but this is a major project, as a whole set of functions need to be rewritten.

For now, however, I would like to have a comment reflecting what is, and maybe add a comment for this TODO. We still have it here: #1147

[andrewwinters5000]

Same here. I would like to avoid unnecessary gradients as it wastes computation time and memory. Although, I understand that having a gradient vector of variables that is one less than the conservative variable vector could be an annoying restructuring of the existing code.

[andrewwinters5000]

Similar here. Changing this commented code goes against the original intent in its creation. We discussed several years ago to mimic the computation of the gradients to match FLUXO. Perhaps we are willing to eat the computational overhead of computing unused gradients, but this is something we should discuss as a group.

[andrewwinters5000]

Same in 3D.