FA-87003 / Physics integrator stability / Member archive

RK4 second stage samples the forcing at the start of the step · case 03

Driven oscillators lag the drive phase and resonance peaks shift.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

solve(x0, v0, k, c, F, wf, dt, steps): unit mass x''=-k*x-c*v+F*cos(wf*t) with wf in rad/s, t starting at 0, integrated with classical RK4. Return [x, v, t] 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	`[0.471037, 0.195307, 0.2]`	`[0.470821, 0.193297, 0.2]`	Failed

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

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