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From "Mike Drob (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-2494) Stat calculation of STDEV may be inaccurate
Date Wed, 19 Mar 2014 20:11:48 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-2494?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13940922#comment-13940922
] 

Mike Drob commented on ACCUMULO-2494:
-------------------------------------

re: fix version

The latest version of the patch delegates all calculations in Stat to commons-math. However,
1.4 does not yet have a dependency on commons-math so I am hesitant to introduce one. [~busbey]
suggested on RB that we apply a known issue note to 1.4 (presumably javadoc?) and then apply
the code change in 1.5 and newer.

[~kturner] - You expressed some concern previously, can you articulate it further?

> 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
>
> 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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