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Linear regression slope rational · case 02

The ratio of means incorrectly forces the fitted line through zero.

Member previewVariant 2 · 3 implementations · 4 checks per implementation

Case contract

Integer finite observations and equal lengths for paired samples. Counts and weights are nonnegative. Rational results use reduced Fraction strings. Empty or undefined statistics return None where shown. Fit y=intercept+slope*x by least squares; return None when x variance is zero, including empty input. Exact operational definition: str(Fraction(len(x)*sum(a*b for a,b in zip(x,y))-sum(x)*sum(y),len(x)*sum(a*a for a in x)-sum(x)**2)) if len(x)*sum(a*a for a in x)!=sum(x)**2 else None

Why this case matters

Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Statistical estimators results depend on the stated convention.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
fixture 1: ([1, 2, 3], [3, 5, 7])	`"5/2"`	`"2"`	Failed

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