Sean Owen created MATH-1058:
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Summary: Beta, LogNormalDistribution, WeibullDistribution give
slightly wrong answer for extremely small args due to log/exp inaccuracy
Key: MATH-1058
URL: https://issues.apache.org/jira/browse/MATH-1058
Project: Commons Math
Issue Type: Bug
Affects Versions: 3.2
Reporter: Sean Owen
Priority: Minor
Background for those who aren't familiar: math libs like Math and FastMath have
two mysterious methods, log1p and expm1. log1p(x) = log(1+x) and expm1(x) =
exp(x)-1 mathetmatically, but can return a correct answer even when x was
small, where floating-point error due to the addition/subtraction introduces a
relatively large error.
There are three instances in the code that can employ these specialized methods
and gain a measurable improvement in accuracy. See patch and tests for an
example -- try the tests without the code change to see the error.
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