FA-87212 / Physics integrator stability / Member archive

Normal impulse clamps the increment instead of the accumulated total · case 02

Warm-started contacts can never reduce their impulse and stacks pop apart.

Member previewVariant 2 · 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 1	`[[0.575, 1.81], [-0.311075, -0.97921], 1.607035, 0.769299]`	`[[0.0, 0.912007], [-0.0, -0.493396], 0.0, 1.638705]`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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