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Factor-out constant calculation. (GH-29491)

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Raymond Hettinger 2021-11-09 10:30:06 -06:00 committed by GitHub
parent 5b7c7cb104
commit c3bc0fe5a6
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1 changed files with 4 additions and 2 deletions
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6
Lib/statistics.py
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@ -139,6 +139,8 @@
from operator import itemgetter, mul
from collections import Counter, namedtuple
_SQRT2 = sqrt(2.0)
# === Exceptions ===
class StatisticsError(ValueError):
@ -1102,7 +1104,7 @@ def cdf(self, x):
"Cumulative distribution function. P(X <= x)"
if not self._sigma:
raise StatisticsError('cdf() not defined when sigma is zero')
return 0.5 * (1.0 + erf((x - self._mu) / (self._sigma * sqrt(2.0))))
return 0.5 * (1.0 + erf((x - self._mu) / (self._sigma * _SQRT2)))
def inv_cdf(self, p):
"""Inverse cumulative distribution function. x : P(X <= x) = p
@ -1158,7 +1160,7 @@ def overlap(self, other):
dv = Y_var - X_var
dm = fabs(Y._mu - X._mu)
if not dv:
return 1.0 - erf(dm / (2.0 * X._sigma * sqrt(2.0)))
return 1.0 - erf(dm / (2.0 * X._sigma * _SQRT2))
a = X._mu * Y_var - Y._mu * X_var
b = X._sigma * Y._sigma * sqrt(dm * dm + dv * log(Y_var / X_var))
x1 = (a + b) / dv