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From Thorsten Schäfer (JIRA) <j...@apache.org>
Subject [jira] [Created] (MATH-1315) MultiKMeansPlusPlusClusterer buggy for alternative evaluators
Date Sun, 10 Jan 2016 18:18:39 GMT
Thorsten Schäfer created MATH-1315:
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             Summary: 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


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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