Add warning about polynomial degree 0

[benegee]

I was misled by a comment in basis_lobatto_legendre.jl, thinking polydeg = 0 would be an exceptional but valid setting. It however only works with TreeMesh. See #1489

So I extended the comment.

Would there be an easy way to catch such a setting early and warn users?

[github-actions]

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[ranocha]

Thanks!

Would there be an easy way to catch such a setting early and warn users?

That would be a bit difficult since it depends on the solver and the mesh. The only safe way would be to add a check to inner constructors of our semidiscretizations (hyperbolic and parabolic) - some kind of check_consistency(mesh, equations, solver) or so. Then, this check could print a warning for polydeg = 0 on the other mesh types.

[benegee]

Would we want to have such checks? What is our policy in regard to user assistance?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.30%. Comparing base (4bf61a0) to head (607c70a).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1863      +/-   ##
==========================================
- Coverage   96.30%   96.30%   -0.00%     
==========================================
  Files         438      438              
  Lines       35577    35603      +26     
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+ Hits        34259    34284      +25     
- Misses       1318     1319       +1     

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[ranocha]

Would we want to have such checks? What is our policy in regard to user assistance?

I would be fine having such a check. Right now, we just check that the dimensions fit

Trixi.jl/src/semidiscretization/semidiscretization_hyperbolic.jl

Line 44 in b11bc10

@assert ndims(mesh) == ndims(equations)

What about the other core devs, e.g., @trixi-framework/principal-developers?

[sloede]

Intuitively, I am not a big fan. One would have to add mesh-specific checks to the semidiscretization, which I don't think is good practice regarding modularity and extensibility.

[ranocha]

Good point.