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Posted to issues@commons.apache.org by "Aleksei Dievskii (JIRA)" <ji...@apache.org> on 2015/11/19 11:19:10 UTC

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

    [ https://issues.apache.org/jira/browse/MATH-1293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15013226#comment-15013226 ] 

Aleksei Dievskii edited comment on MATH-1293 at 11/19/15 10:18 AM:
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At that moment, no. I was operating under assumption that I can send messages to the list without being subscribed. Presently, I have successfully subscribed and re-sent my message. However, it has yet to appear in the archive or be otherwise acknowledged.


was (Author: dievsky):
At that moment, no. I was operating under assumption that I can send messages to the list without being subscribed. Presently, I have successfully subscribed and re-sent my message.

> 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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