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From "Nate Paymer (JIRA)" <j...@apache.org>
Subject [jira] Created: (MATH-547) KMeansPlusPlusClusterer should not call equals()
Date Sat, 12 Mar 2011 05:05:59 GMT
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
            Priority: Minor


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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