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Posted to issues@commons.apache.org by "Gilles (JIRA)" <ji...@apache.org> on 2015/12/19 18:44:46 UTC

[jira] [Commented] (MATH-1293) Tabulating the logarithmic factorial

    [ https://issues.apache.org/jira/browse/MATH-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15065449#comment-15065449 ] 

Gilles commented on MATH-1293:
------------------------------

Feature committed as 00439211981af7b5baed495f526ef8ad76ee7c5b on "master" branch (4.0).
Please review and let me know if my modifications suit you.  Thanks.

> Tabulating the logarithmic factorial
> ------------------------------------
>
>                 Key: MATH-1293
>                 URL: https://issues.apache.org/jira/browse/MATH-1293
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.5
>            Reporter: Aleksei Dievskii
>            Priority: Minor
>              Labels: feature, patch
>         Attachments: factlog.patch, factlog_ondemand.patch
>
>
> Presently, CombinatoricsUtils#factorialLog is calculated via a tabulated value for the first 21 entries, and for the rest it employs linear-complexity direct summing. For the factorial-heavy computations this can be rather painful. I propose a patch which allocates additional 16KB of tabulated log-factorial values, allowing very fast (constant complexity) computation for arguments up to 17000, and delegating to the log-gamma for the rest. Benchmarks show a speed-up of up to 200x.



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