FA-16207 / Floating-point arithmetic / Member archive

Inverse tangent loses tiny input in a logarithmic ratio · case 02

Inverse tangent loses tiny input in a logarithmic ratio.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Evaluate inverse hyperbolic tangent on [-1,1], with signed infinite endpoints and a domain marker outside. Finite results are rendered to eleven significant decimal digits; modeled domain violations and arithmetic errors are explicit strings.

Why this case matters

An offline floating representation model isolates a reproducible arithmetic fault.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
tiny positive	`"0"`	`"1.734723476e-18"`	Failed

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