Sean Owen created MAHOUT-1239:
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Summary: Standardize form of log-likelihood computation
Key: MAHOUT-1239
URL: https://issues.apache.org/jira/browse/MAHOUT-1239
Project: Mahout
Issue Type: Improvement
Affects Versions: 0.7
Reporter: Sean Owen
Priority: Minor
Fix For: 0.8
Attachments: MAHOUT-1239.patch
[email protected] reported that LogLikelihood.logLikelihoodRatio() looked like
its formula was incorrect, at least with respect to
http://tdunning.blogspot.mx/2008/03/surprise-and-coincidence.html
It appears that the calculation is correct but in a different form, that is not
immediately recognizable as correct. The proposal here is to change the code to
match the blog post and avoid confusion (and ends up avoiding 2 method calls).
(Along the way, I think this fixes a tiny other problem in a related test. We
have a test case that detects when round-off would produce a negative LLR and
should be clamped to 0, but the test asserts that the result is >0 not >=0.)
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