For now, this is too much of a change for too little gains. Doing a final pass, otherwise I'll close this PR

Update (commit 5184a38): added opt-in fast modes and more CPU reductions.\n\n- New : .\n - : x64 off + shape_factor=1 + J filter none + forces all outputs off + compiles full-run when possible.\n - : same as aggressive + forces (explicitly a physics approximation).\n- now uses the numerically-stable relativistic KE formula so fp32 fast modes don’t produce negative kinetic energies.\n- Fixed 2D stacked-field interpolation broadcasting (multi-component interpolation now expands weights).\n\nTwo-stream long bench (CPU, , , plotting disabled):\n- origin/main: (from CLI output)\n- fast_mode=aggressive: (~3.2×)\n- fast_mode=extreme: (~3.6×)\n\nI’m still not seeing a physics-preserving path to a true 5×+ on this workload without a much larger refactor (e.g., monolithic particle state like JAX-in-Cell) or additional physics approximations (electrostatic / frozen species / non-relativistic).

Update (commit 5184a38): added opt-in fast modes and more CPU reductions.

• New simulation_parameters.fast_mode: off|fp32|aggressive|extreme.
  • aggressive: x64 off + shape_factor=1 + J filter none + forces all outputs off + compiles full-run when possible.
  • extreme: same as aggressive + forces relativistic=false (explicitly a physics approximation).
• compute_energy now uses the numerically-stable relativistic KE formula m c^2 (gamma-1) so fp32 fast modes don’t produce negative kinetic energies.
• Fixed 2D stacked-field interpolation broadcasting (multi-component interpolation now expands weights).

Two-stream long bench (CPU, t_wind=5.413e-7, Nx=100,Ny=1,Nz=1, plotting disabled):

• origin/main: 7.787e-4 s/step (from CLI output)
• fast_mode=aggressive: 2.434e-4 s/step (~3.2×)
• fast_mode=extreme: 2.162e-4 s/step (~3.6×)

I’m still not seeing a physics-preserving path to a true 5×+ on this workload without a much larger refactor (e.g., monolithic particle state like JAX-in-Cell) or additional physics approximations (electrostatic / frozen species / non-relativistic).