FA-64927 / Epidemic compartment models / Member archive

Reed-Frost expected chain-binomial generations: escape probability · case 02

Expected cases exceed the susceptible pool when several infectives are present.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Expected Reed-Frost: C[t+1] = S[t]*(1-(1-p)**C[t]), S[t+1]=S[t]-C[t+1]; cases are infectious for one generation only; stop early once expected cases fall below 1e-9; return [cases per generation including the index generation rounded to 4, final size including index cases rounded to 4]; None for invalid p or negative counts.

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: fading chain	`[[1.0, 0.6, 0.3528, 0.205, 0.1182, 0.0679, 0.0389, 0.0223, 0.0127, 0.0073, 0.0042], 2.4293]`	`[[1.0, 0.6, 0.3542, 0.2071, 0.1204, 0.0698, 0.0404, 0.0233, 0.0135, 0.0078, 0.0045], 2.4409]`	Failed

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