[ https://issues.apache.org/jira/browse/MATH-849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13504031#comment-13504031 ]
Sébastien Brisard commented on MATH-849:
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As of {{r1413802}}, {{Gamma.gamma(x)}} returns {{Double.NaN}} if {{x}} is a negative integer.
> Precision improvement in class Gamma
> ------------------------------------
>
> Key: MATH-849
> URL: https://issues.apache.org/jira/browse/MATH-849
> Project: Commons Math
> Issue Type: Improvement
> Reporter: Sébastien Brisard
> Assignee: Sébastien Brisard
> Priority: Minor
> Labels: accuracy, special-functions
> Fix For: 3.1
>
> Attachments: MATH-849-Lanczos_vs_NSWC.zip, MATH-849.patch, MATH-849.zip
>
>
> New unit tests (see below) show that (on the set of values tested) the current accuracy of {{Gamma.logGamma(double)}} is about 130 ulps.
> The [NSWC Library of Mathematical Functions|http://www.dtic.mil/docs/citations/ADA476840] proposes an implementation of this function with much higher accuracy: on the same set of values, the error goes down to about 3 ulps.
> This library is available [here|http://www.ualberta.ca/CNS/RESEARCH/Software/NumericalNSWC/site.html], and is license-free [see this thread|http://markmail.org/thread/fg4y4dfdnfty5hov]. It is proposed to port this implementation in Commons-Math. This in turn could lead to a resolution of MATH-738.
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