FA-87235 / Physics integrator stability / Member archive

Friction impulse increment has the sliding direction sign reversed · case 05

Friction accelerates sliding instead of opposing it.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

solve(vn0, vt0, w, mu, iterations, cached, warm): several contact points share one relative normal and tangent velocity with inverse mass w. Warm start each point with warm*cached [jn, jt] and apply it to the velocities. Each iteration visits points in order: friction first (accumulated jt clamped to |jt|<=mu*jn), then normal (accumulated jn clamped >=0). Return [jn list, jt list, vn, vt] rounded to 6.

Why this case matters

Game and robotics physics loops depend on integrator update order, step control and stabilization terms; a wrong decision point turns a stable simulation into drifting or exploding motion.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
case 0	`[[1.093661], [-0.007413], -0.0, -0.68598]`	`[[1.093661], [0.007413], -0.0, -0.66002]`	Failed

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