Skip to content

Physics numerical policy (language surface)

Status: Planned phase PHY-n — library types ship in li-std-physics-core; compiler elaboration not wired.

User-facing goals

  1. Declare fidelity tier, timestep budget, and error targets once per simulation or def.
  2. Compiler selects integrator, stencil, and solver at compile time from a closed table.
  3. Reject unstable combinations (dt vs CFL, non-symplectic + long energy bound).

Surface (draft)

@physics(tier = simulation, fps = 60)
def advance(world: PhysicsWorld, dt: float) -> unit
  targets energy_drift < 1e-3
  targets momentum_drift < 1e-4
  requires dt > 0

Elaboration

Input Pass Output MIR
tier = arcade dt, targets Semi-implicit Euler, loose drift
tier = simulation CFL for hyperbolic if grid Verlet / WCSPH
tier = scientific dt halving proof optional RK4 / CN / FDTD

Depends on

  • 2i / 7e — math lowering
  • 7d — @physics decorator slot (or reserved name alongside @cpu)
  • 2e / 2f — targets as proof obligations where provable

Tests

  • li-tests/physics_policy/ — reject illegal tier+target pairs
  • Extend benchmarks/harness/stability.py per method class

Agent workflow

Use skill research-li-numerics before extending the selection table.