Default BC functions for P4est , Tree and Structured meshes

[vincmarks]

Changes

• New boundary-condition functions added

  • boundary_condition_default_p4est_2D
  • boundary_condition_default_p4est_3D
  • boundary_condition_default_structured_1D
  • boundary_condition_default_structured_2D
  • boundary_condition_default_structured_3D
  • boundary_condition_default_tree_1D
  • boundary_condition_default_tree_2D
  • boundary_condition_default_tree_3D
    These functions apply the same boundary condition on every face of the mesh for P4est, structured, and tree meshes.

• Documentation updated

  • Added a Boundary Condition section to the following pages:
    • Trixi.jl/docs/src/meshes/p4est_mesh.md
    • Trixi.jl/docs/src/meshes/structured_mesh.md
    • Trixi.jl/docs/src/meshes/tree_mesh.md

[github-actions]

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Created with ❤️ by the Trixi.jl community.

[JoshuaLampert]

Thanks for the contribution! Would it maybe be a cleaner interface to have only one function boundary_condition_default(mesh, boundary_condition) , which dispatches on the mesh type? Then you can use another mesh, but still get the correct default boundary condition. This goes into the direction of #1510.
Could you also use the new functions in at least one of the elixirs each, such that they are tested?

[DanielDoehring]

Thanks for your contribution!

I like the convenience, but maybe we start with the non-tree mesh types since for the latter (as you mentioned) this functionality actually already exists

Trixi.jl/examples/tree_2d_dgsem/elixir_advection_amr_nonperiodic.jl

Lines 12 to 26 in 3ce2033

	# you can either use a single function to impose the BCs weakly in all
	# 2*ndims == 4 directions or you can pass a tuple containing BCs for each direction
	boundary_conditions = BoundaryConditionDirichlet(initial_condition)
	solver = DGSEM(polydeg = 3, surface_flux = flux_lax_friedrichs)
	coordinates_min = (-5.0, -5.0)
	coordinates_max = (5.0, 5.0)
	mesh = TreeMesh(coordinates_min, coordinates_max,
	initial_refinement_level = 4,
	n_cells_max = 30_000,
	periodicity = false)
	semi = SemidiscretizationHyperbolic(mesh, equations, initial_condition, solver,
	boundary_conditions = boundary_conditions)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.81%. Comparing base (1d75f8f) to head (f5538da).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2515   +/-   ##
=======================================
  Coverage   96.81%   96.81%           
=======================================
  Files         535      536    +1     
  Lines       42813    42829   +16     
=======================================
+ Hits        41446    41462   +16     
  Misses       1367     1367           

Flag	Coverage Δ
unittests	96.81% <100.00%> (+<0.01%)	⬆️

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[JoshuaLampert]

Some more formatting comments below (you can also go to the "Files changed" tab and add suggestions to a batch, such that multiple suggestions can be bundled in one commit to keep the commit history clean).

[vincmarks]

Some more formatting comments below (you can also go to the "Files changed" tab and add suggestions to a batch, such that multiple suggestions can be bundled in one commit to keep the commit history clean).

Thanks for the comments and the idea with the batch 👍

[ranocha]

Could you please switch to a dispatch-based approach instead of having if statements based on the type? This makes it easier to extend the functionality in the future. For example, you would write

function boundary_condition_default(mesh::TreeMesh1D, boundary_condition)
    return (x_neg = boundary_condition,
            x_pos = boundary_condition)
end

and remove the functions boundary_condition_default_tree_1D etc.

[ranocha]

Suggested change

	end#@muladd
	end # @muladd

Please revert the whitespace change.

[ranocha]

Thanks! We are close to merging this PR.