Expectation Maximization

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Presentation transcript:

Expectation Maximization Lecture 10 Expectation Maximization

A simple clustering problem Naive Bayes has labels observed. What if they are hidden? Mixture model with labels from Bernoulli and data from Gaussian (2 classes). Observation: the summation appears inside the log: trouble for optimization (not so for naive Bayes!). Rewrite the derivative of log-L such that summation moves outside log  fixed point equations. Simple updates, but do they converge and do the improve L (note similarity with IS).

EM as Bound Optimization Use Jensen inequality to compute a bound on log-L. E-step: compute bound Q M-step: optimize bound Example: the color-blind man drawing colored balls. demo_EM(p,N).