Improve Scalability of Gaussian Cluster For Wide Vectors
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Key: MAHOUT-846
URL: https://issues.apache.org/jira/browse/MAHOUT-846
Project: Mahout
Issue Type: Improvement
Affects Versions: 0.5
Reporter: Jeff Eastman
Assignee: Jeff Eastman
Fix For: 0.6
The pdf() implementation in GaussianCluster is pretty lame. It is computing a
running product of the element pdfs which, for wide input vectors (Reuters is
41,807), always underflows and returns 0. Here's the code:
public double pdf(VectorWritable vw) {
Vector x = vw.get();
// return the product of the component pdfs
// TODO: is this reasonable? correct? It seems to work in some cases.
double pdf = 1;
for (int i = 0; i < x.size(); i++) {
// small prior on stdDev to avoid numeric instability when stdDev==0
pdf *= UncommonDistributions.dNorm(x.getQuick(i),
getCenter().getQuick(i), getRadius().getQuick(i) + 0.000001);
}
return pdf;
}
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