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

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.3
• Fix Version/s: 3.4
• Labels: easyfix
• Assignee: Unassigned
• Reporter: Pashutan Modaresi
• Created: 06/Nov/14 11:57
• Updated: 26/Dec/14 19:50
• Resolved: 07/Nov/14 22:10

Description

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;