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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2494) Stat calculation of STDEV may be inaccurate
Date Tue, 25 Mar 2014 01:59:45 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13946018#comment-13946018
] 

Josh Elser commented on ACCUMULO-2494:
--------------------------------------

bq. Which version of Hadoop did you use?

Apache Hadoop 2.3.0. Looks like they bundle a commons-math3 (which contains a {{org/apache/commons/math3/stat/descriptive/rank/Min}}
but not {{org/apache/commons/math/stat/descriptive/rank/Min}}). Taking a step to assume that
you're asking because you expected it to be provided by Hadoop.. haven't we moved away from
this due to the lessons learned from 1.5.0 (the original emphasis that since we're using it
directly, we should provide it directly)?

> Stat calculation of STDEV may be inaccurate
> -------------------------------------------
>
>                 Key: ACCUMULO-2494
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2494
>             Project: Accumulo
>          Issue Type: Bug
>          Components: client
>            Reporter: Mike Drob
>            Assignee: Mike Drob
>             Fix For: 1.5.2, 1.6.0
>
>
> The math is sound, but it is susceptible to rounding errors. We should address that.
> See http://www.strchr.com/standard_deviation_in_one_pass and http://www.cs.berkeley.edu/~mhoemmen/cs194/Tutorials/variance.pdf



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