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From "Gilles (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-1315) MultiKMeansPlusPlusClusterer buggy for alternative evaluators
Date Tue, 17 May 2016 16:46:13 GMT

    [ https://issues.apache.org/jira/browse/MATH-1315?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15286982#comment-15286982
] 

Gilles commented on MATH-1315:
------------------------------

Hi Thorsten.

Can you contribute a unit test to ensure that the fix is working?  Thanks.

> MultiKMeansPlusPlusClusterer buggy for alternative evaluators
> -------------------------------------------------------------
>
>                 Key: MATH-1315
>                 URL: https://issues.apache.org/jira/browse/MATH-1315
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.5
>            Reporter: Thorsten Schäfer
>         Attachments: MATH-1315.patch
>
>
> I just looked into the source code for the MultiKMeansPlusPlusClusterer and realized
that it would return null in case of an alternative evaluator that favors bigger values instead
of smaller ones:
> The basic idea of the clustering method is that we perform n clusterings and choose the
best result. The decision what's the best result is performed by the evaluator, which by default
assumes smaller values are better. 
> According to the documentation, we can also provide a different evaluator, which for
instance would decide that bigger values are better, but given we initialize the best value
with Double.POSITIVE_INFINITY in method MultiKMeansPlusPlusClusterer.cluster(Collection<T>),
we would never find a "better" result and thus always return null. 



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