FA-64949 / Epidemic compartment models / Member archive

Reed-Frost expected chain-binomial generations: final size accounting · case 04

The final size misses the index cases.

Member previewVariant 4 · 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: household of 10	`[[1.0, 0.9, 0.7328, 0.5474, 0.3822, 0.2541, 0.1633], 2.9798]`	`[[1.0, 0.9, 0.7328, 0.5474, 0.3822, 0.2541, 0.1633], 3.9798]`	Failed

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