[MAHOUT-1239] Standardize form of log-likelihood computation

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.7
• Fix Version/s: 0.8
• Assignee: Sean R. Owen
• Reporter: Sean R. Owen
• Due: 04/Jun/13
• Created: 03/Jun/13 20:40
• Updated: 02/Mar/14 20:17
• Resolved: 04/Jun/13 00:19

Description

[e-mail] 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.)

Issue Links

• supercedes: MAHOUT-1257 performance improvement to LogLikehood