Pashutan Modaresi created MATH-1165:
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Summary: 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
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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