[jira] [Created] (MATH-1315) MultiKMeansPlusPlusClusterer buggy for alternative evaluators

["Thorsten Schäfer (JIRA)" <ji...@apache.org>]

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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