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From "Thomas Neidhart (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-1165) Rare case for updateMembershipMatrix() in FuzzyKMeansClusterer
Date Thu, 06 Nov 2014 14:59:34 GMT

    [ https://issues.apache.org/jira/browse/MATH-1165?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14200256#comment-14200256
] 

Thomas Neidhart commented on MATH-1165:
---------------------------------------

This can only happen if the clusterer is initialized to form exactly 1 cluster and is then
fed with only 1 data point.

It is quite unlikely that somebody will use the clusterer in that way, but we will fix this
rare case.

> Rare case for updateMembershipMatrix() in FuzzyKMeansClusterer
> --------------------------------------------------------------
>
>                 Key: MATH-1165
>                 URL: https://issues.apache.org/jira/browse/MATH-1165
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.3
>            Reporter: Pashutan Modaresi
>            Priority: Minor
>              Labels: easyfix
>   Original Estimate: 1h
>  Remaining Estimate: 1h
>
> The function updateMembershipMatrix() in FuzzyKMeansClusterer assigns the points to the
cluster with the highest membership. Consider the following case:
> If the distance between a point and the cluster center is zero, then we will have a cluster
membership of one, and all other membership values will be zero.
> So the if condition:
> if (membershipMatrix[i][j] > maxMembership) {
>                     maxMembership = membershipMatrix[i][j];
>                     newCluster = j;
> }
> will never be true during the for loop and newCluster will remain -1. This will throw
an exception because of the line:
> clusters.get(newCluster)
>                     .addPoint(point);
> Adding the following condition can solve the problem:
> double d;
> if (sum == 0)
> d = 1;
> else
> d = 1.0/sum;



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