FA-65428 / Ecological population dynamics / Member archive

Lotka-Volterra predator-prey Euler integration: non-negativity floor · case 03

Large steps drive prey negative, which then feeds predators negatively.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

dx = alpha*x - beta*x*y, dy = delta*x*y - gamma*y evaluated from the same start-of-step state; Euler update with each population floored at 0; return [path of [x,y] rounded 4 including start, coexistence equilibrium [gamma/delta, alpha/beta] rounded 4 or None when beta or delta is not positive].

Why this case matters

Population projections set harvest quotas, conservation status and pest-control timing; a wrong update order, boundary or rate conversion silently changes management advice.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: large step overshoot	`[[[10.0, 50.0], [-35.0, 40.0], [87.5, 0.0], [131.25, 0.0], [196.875, 0.0]], [20.0, 5.0]]`	`[[[10.0, 50.0], [0.0, 40.0], [0.0, 24.0], [0.0, 14.4], [0.0, 8.64]], [20.0, 5.0]]`	Failed

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