Store capacity serial tree mesh

[DanielDoehring]

This change saves the capacity of a (serial) tree mesh in the restart file and is retrieved later on.

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5c08cf4) 89.92% compared to head (5d142bc) 72.89%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1748       +/-   ##
===========================================
- Coverage   89.92%   72.89%   -17.03%     
===========================================
  Files         431      431               
  Lines       34854    34863        +9     
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- Hits        31339    25411     -5928     
- Misses       3515     9452     +5937     

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[sloede]

Sorry, but I don't fully get it: What's the purpose of this change? One still needs to provide n_cells_max to load_mesh_serial, so what do I save here?

[DanielDoehring]

No, not at all: If you do not provide n_cells_max in the load_mesh call, it will now set the original value for capacity and not the current number of cells.

Concrete example:

The mesh loaded here

Trixi.jl/examples/tree_2d_dgsem/elixir_advection_restart.jl

Line 19 in a3f3884

mesh = load_mesh(restart_filename)

is of the form

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ TreeMesh{2, Trixi.SerialTree{2}}                                                                 │
│ ════════════════════════════════                                                                 │
│ center: …………………………………………………………… [0.0, 0.0]                                                       │
│ length: …………………………………………………………… 2.0                                                              │
│ periodicity: ……………………………………………… (true, true)                                                     │
│ current #cells: ……………………………………… 341                                                              │
│ #leaf-cells: ……………………………………………… 256                                                              │
│ maximum #cells: ……………………………………… 341                                                              │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

while the mesh loaded with the proposed change has fields

┌──────────────────────────────────────────────────────────────────────────────────────────────────┐
│ TreeMesh{2, Trixi.SerialTree{2}}                                                                 │
│ ════════════════════════════════                                                                 │
│ center: …………………………………………………………… [0.0, 0.0]                                                       │
│ length: …………………………………………………………… 2.0                                                              │
│ periodicity: ……………………………………………… (true, true)                                                     │
│ current #cells: ……………………………………… 341                                                              │
│ #leaf-cells: ……………………………………………… 256                                                              │
│ maximum #cells: ……………………………………… 30000                                                            │
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

since we store

Trixi.jl/examples/tree_2d_dgsem/elixir_advection_extended.jl

Line 29 in a3f3884

n_cells_max = 30_000, # set maximum capacity of tree data structure

I prefer the proposed change very much since the current version will cause your AMR simulation to crash.

[sloede]

Thanks for the explanation!

[sloede]

The proper solution to the described issue would of course be to implement/fix #486. In the meantime, this sounds like a good idea for a quick fix of the capacity/n_cells_max issue when doing restarts.

With the two comments resolved, this LGTM!