FA-84438 / Betting odds conversion / Member archive

Power-method bisection moves the wrong bracket end · case 03

The power exponent converges to 1 or 10 and the fair probabilities do not sum to one.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Remove the bookmaker margin from decimal prices (implied p = 1/d, book = sum p > 1 assumed). multiplicative: p / book. additive: p - (book - 1) / n; if any result is negative return "additive infeasible". power: p ** k with k found by 60 bisection steps on [1, 10] so that the powered probabilities sum to 1 (k = midpoint of the final bracket). Any other method returns "invalid method". Return the fair probabilities formatted "%.4f".

Why this case matters

Pricing models strip margins differently; favourite-longshot bias makes the method matter.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
control power	`["0.0028", "0.0010"]`	`["0.5285", "0.4715"]`	Failed

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