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SIR Euler integrator with daily sampling: day indexing · case 04

Peak days are reported one day early and the run stops one day short in its own numbering.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Frequency-dependent SIR integrated with forward Euler at dt=1/substeps; new infections per substep are beta*S*I/pop*dt capped at S; peak prevalence and its day are sampled at day ends (day 0 is the seed); return [S, peak I, peak day, R] rounded to 3 decimals, or None for invalid input.

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: slow recovery long run	`[19.331, 965.817, 42, 1829.639]`	`[19.331, 965.817, 43, 1829.639]`	Failed

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