How to compute similarity using the log-likelihood similarity metric with mathematics formula？？
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Item   101 102 103 104 105 106 107     Similarity to User1
user1   x   x   x                             0.9
user2   x   x   x   x                         0.84 

x means the item is selected    
I want to know how to compute the  log-likelihood similarity? I know Mahout can solve it, however, I do not know the code inside it and still feel puzzle about its mathematics process.
How can I get 0.9 and 0.84??  Thank you very much for your reply!!