[
https://issues.apache.org/jira/browse/MAHOUT-846?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Jeff Eastman updated MAHOUT-846:
--------------------------------
Description:
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:
{noformat}
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;
{noformat}
}
was:
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;
}
> Improve Scalability of Gaussian Cluster For Wide Vectors
> --------------------------------------------------------
>
> 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:
> {noformat}
> 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;
> {noformat}
> }
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