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From "Aleksei Dievskii (JIRA)" <>
Subject [jira] [Commented] (MATH-1293) Tabulating the logarithmic factorial
Date Fri, 20 Nov 2015 16:03:10 GMT


Aleksei Dievskii commented on MATH-1293:

While the jury is still out, I made another variant of the patch, conforming to Gilles' suggestion.
I attach it to the issue under the name "factlog_ondemand.patch".

> Tabulating the logarithmic factorial
> ------------------------------------
>                 Key: MATH-1293
>                 URL:
>             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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