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https://issues.apache.org/jira/browse/MATH-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15011295#comment-15011295
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Aleksei Dievskii commented on MATH-1293:
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Thank you for your advice! However, I'm not exactly sure how to do this. I've
sent an email to [email protected], but it hasn't shown up in the archive
at https://mail-archives.apache.org/mod_mbox/commons-dev/201511.mbox/browser .
Is it the wrong way to reach the mailing list?
> 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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