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https://issues.apache.org/jira/browse/NUMBERS-179?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved NUMBERS-179.
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Fix Version/s: 1.1
Resolution: Implemented
Updated in commit:
842c4b80ccac4ca218a260194f4f955f344fd243
> Optimise the choice of function for the gamma P derivative
> ----------------------------------------------------------
>
> Key: NUMBERS-179
> URL: https://issues.apache.org/jira/browse/NUMBERS-179
> Project: Commons Numbers
> Issue Type: Improvement
> Components: gamma
> Affects Versions: 1.1
> Reporter: Alex Herbert
> Priority: Minor
> Fix For: 1.1
>
>
> The incomplete gamma function is evaluated using the Lanczos approximation.
> This is evaluated using two alternate expressions when the terms a and z are
> large:
> See [Incomplete Gamma Eq. 15 and Eq.
> 16|https://www.boost.org/doc/libs/1_78_0/libs/math/doc/html/math_toolkit/sf_gamma/igamma.html]
> The defaults used in the Boost C++ implementation required updating to
> increase the precision of the function when a=142 for [STATISTICS-39]. The
> threshold for large a was lowered from 150 to 100. The switch between the two
> functions requires optimisation to ensure the threshold is applicable to
> other parameterisations, e.g. a from 50 to 150.
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