FA-65005 / Epidemic compartment models / Member archive

Two-group next-generation matrix R0: target-group size weighting · case 05

Small high-contact groups dominate R0 even when few susceptibles are in them.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

K[i][j] = contact[i][j]*sizes[i]/sum(sizes)/gamma[j] (infections in group i caused by one infective in j); R0 is the dominant eigenvalue of the 2x2 K; lead group is the larger component of its eigenvector (ties and decoupled ties to group 0); return [flattened K rounded 6, R0 rounded 6, lead] or None for empty population or non-positive gamma.

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: asymmetric core group	`[[1.333333, 0.9, 0.333333, 1.35], 1.889453, 0]`	`[[1.333333, 0.1, 3.0, 1.35], 1.889453, 1]`	Failed

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