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From "Pashutan Modaresi (JIRA)" <>
Subject [jira] [Created] (MATH-1164) Rare case for updateMembershipMatrix() in FuzzyKMeansClusterer
Date Thu, 06 Nov 2014 11:58:33 GMT
Pashutan Modaresi created MATH-1164:

             Summary: Rare case for updateMembershipMatrix() in FuzzyKMeansClusterer
                 Key: MATH-1164
             Project: Commons Math
          Issue Type: Bug
    Affects Versions: 3.3
            Reporter: Pashutan Modaresi
            Priority: Minor

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:

Adding the following condition can solve the problem:
double d;
if (sum == 0)
d = 1;
d = 1.0/sum;

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