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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MATH-546) Truncation issue in KMeansPlusPlusClusterer
Date Tue, 15 Mar 2011 12:33:29 GMT

    [ https://issues.apache.org/jira/browse/MATH-546?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13006894#comment-13006894
] 

Luc Maisonobe commented on MATH-546:
------------------------------------

The empty cluster strategy is needed regardless of this bug. It may appear with different
conditions and is a feature commonly found in clustering implementations.
This issue can be marked as resolved if the patch has been applied and works.

Thanks to Nate for reporting and fixing the issue, thanks to Gilles for reviewing and applying
the patch.

> Truncation issue in KMeansPlusPlusClusterer
> -------------------------------------------
>
>                 Key: MATH-546
>                 URL: https://issues.apache.org/jira/browse/MATH-546
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Nate Paymer
>            Priority: Minor
>              Labels: cluster
>         Attachments: MATH-546.txt
>
>
> The for loop inside KMeansPlusPlusClusterer.chooseInitialClusters defines a variable
>   int sum = 0;
> This variable should have type double, rather than int.  Using an int causes the method
to truncate the distances between points to (square roots of) integers.  It's especially bad
when the distances between points are typically less than 1.
> As an aside, in version 2.2, this bug manifested itself by making the clusterer return
empty clusters.  I wonder if the EmptyClusterStrategy would still be necessary if this bug
were fixed.

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