CollisionOperators

Implementations of various collision operators such as Landau or Lenard–Bernstein.

2D Lenard–Bernstein operator

Structure-preserving particle discretisation of the conservative 2D Lenard–Bernstein operator: the density is reconstructed in a tensor-product B-spline finite-element space (via Mantis), particles are advected by implicit midpoint, and a 3×3 Lagrange-multiplier system enforces exact discrete conservation of momentum and energy. Follows Jeyakumar et al. (2024). See the documentation for the scheme and the conservation algebra.

Source layout

File	Role
main_LB.jl	Driver: time loop, implicit solve (Picard / Anderson), checkpointing, CSV + PNG output
functions.jl	LB physics: L² projection, log-gradient, drift multipliers, velocity update, diagnostics
MantisWrappers.jl	FEM scaffolding around Mantis (mesh, mass matrix, particle location/evaluation, Workspace)
Parameters.jl	SimParameters struct + CLI override parsing + Gaussian IC sampling
parameters_LB*.jl	Presets, each building a PARAMS::SimParameters
plot_dashboard_LB*.jl, plot_scatter_LB*.jl	Post-processing plots of the CSV output

Run

julia --project=. main_LB.jl parameters_LB2D_v3.jl
# scalar overrides:
julia --project=. main_LB.jl parameters_LB2D_v3.jl --N_STEPS=200 --suffix=foo
# resume from last checkpoint:
julia --project=. main_LB.jl parameters_LB2D_v3.jl --resume=auto

ARGS[1] is the preset file; ARGS[2:] are --key=value scalar overrides. Vector fields (bp1, bp2) are not CLI-overridable — edit the preset.

Output (per suffix)

• conservation_history_<suffix>.csv — one row per step: step,time,entropy,energy,p1,p2,iter,residual,fp_minus_fs,neg_part
• fs_snapshot_<suffix>_step#####.csv — B-spline coefficients of f_s (mesh breakpoints in the header) every snap_every steps + final
• diagnostic PNG + particle dump at each snapshot step