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

["Aleksei Dievskii (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Aleksei Dievskii updated MATH-1293:
-----------------------------------
    Attachment: factlog.patch

The logarithmic factorial patch.

> 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
>
>
> 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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