[jira] [Closed] (MATH-1140) Incorrect result from MannWhitneyUTest#mannWhitneyUTest with large datasets

["Anders Conbere (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-1140?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Anders Conbere closed MATH-1140.
--------------------------------

    Resolution: Fixed

Ouch, somewhat embarrassed to say that our experimental data was just often large enough that we often hit 0 :-/

> Incorrect result from MannWhitneyUTest#mannWhitneyUTest with large datasets
> ---------------------------------------------------------------------------
>
>                 Key: MATH-1140
>                 URL: https://issues.apache.org/jira/browse/MATH-1140
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.3
>            Reporter: Anders Conbere
>            Priority: Minor
>
> On large datasets MannWhitneyUTest#mannWhitneyUTest returns the double value 0.0 instead of the correct p-value. I suspect this is an overflow but haven't been able to trace it down yet.
> I'm afraid I'm not very good at java, but I'm including a link to a public repository where you can reproduce the issue, unfortunately my implementation is written in clojure.
> https://github.com/aconbere/apache-commons-mann-whitney-bug
> The summary is that by calling MannWhitneyUTest#mannWhitneyUTest with two randomly generated arrays (50k elements with a max value of 300) I can reliably reproduce the result 0.0. By reducing that to something more modest  like 2k I get correct p-value calculations.



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