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SIS endemic equilibrium convergence: subthreshold equilibrium · case 02

Subcritical infections report a negative endemic level and never converge.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

SIS with susceptibles pop-I; endemic target pop*(1-1/R0) if R0=beta/gamma>1 else 0; iterate daily Euler I += beta*I*(pop-I)/pop - gamma*I until |I-target| <= tol*pop or max_days steps; return [target rounded 4, days taken, I rounded 4] or None for non-positive beta, gamma or pop.

Why this case matters

Compartmental epidemic calculations drive outbreak forecasts, vaccine targets and hospital planning; a single wrong flow, rate conversion or boundary silently changes every downstream number.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: subcritical dies out	`[-500.0, 200, 0.0]`	`[0.0, 21, 4.9755]`	Failed

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