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https://issues.apache.org/jira/browse/STATISTICS-38?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved STATISTICS-38.
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Resolution: Implemented
> Optimise use of the Gamma function in the PoissonDistribution
> -------------------------------------------------------------
>
> Key: STATISTICS-38
> URL: https://issues.apache.org/jira/browse/STATISTICS-38
> Project: Apache Commons Statistics
> Issue Type: Improvement
> Components: distribution
> Affects Versions: 1.0
> Reporter: Alex Herbert
> Priority: Minor
>
> The Poisson distribution currently allows user configured tolerances for
> computing the Gamma functions for the CDF. These may not be necessary and it
> should be investigated. The version of the Gamma function used by the Poisson
> distribution may not be the same as
> those that required these tolerances in Commons Math 2 (use of the
> tolerances go as far back as the commit history in the git repo).
> Repeated calling of the RegularizedGamma.P and Q functions from numbers would
> benefit from allowing pre-computation of the the log( x ) component in the
> RegularizedGamma function. In this case x is the Poisson mean. See also
> NUMBERS-167 which discusses pre-computation of the LogGamma(a) component of
> the input arguments a and x.
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