[jira] [Resolved] (MATH-1165) Rare case for updateMembershipMatrix() in FuzzyKMeansClusterer

["Thomas Neidhart (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MATH-1165?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Thomas Neidhart resolved MATH-1165.
-----------------------------------
       Resolution: Fixed
    Fix Version/s: 3.4

Fixed in commit 596ccd59a11ad5e9fda19ccd0f4fc714d8d3394d

Thanks for the report!

> 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
>             Fix For: 3.4
>
>   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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