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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (MATH-547) KMeansPlusPlusClusterer should not call equals()
Date Mon, 04 Apr 2011 18:39:05 GMT

     [ https://issues.apache.org/jira/browse/MATH-547?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Luc Maisonobe resolved MATH-547.
--------------------------------

       Resolution: Fixed
    Fix Version/s: 3.0
         Assignee: Luc Maisonobe

Fixed in subversion repository as of r1088702.

Thanks to Nate for identifying the problem and thanks to Thomas for providing the patch

> KMeansPlusPlusClusterer should not call equals()
> ------------------------------------------------
>
>                 Key: MATH-547
>                 URL: https://issues.apache.org/jira/browse/MATH-547
>             Project: Commons Math
>          Issue Type: Improvement
>    Affects Versions: 3.0
>            Reporter: Nate Paymer
>            Assignee: Luc Maisonobe
>            Priority: Minor
>             Fix For: 3.0
>
>         Attachments: MATH-547.patch
>
>
> In determining whether the clusters have changed between iterations, the KMeansPlusPlusClusterer
currently calls equals to determine whether the cluster centers have changed.  It would be
better to avoid relying on equals by instead checking whether any points have moved between
clusters.
> equals can be problematic because floating point operations are not strictly commutative
or associative, so getCentroid may return slightly different values even when called with
the same set of inputs.  Additionally, the client may choose not to override equals at all,
since it's not clear that it's required.

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