E-step

Compute posterior q(z) = P(z|x, θ) over hidden variables given current parameters.

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M-step

Update θ maximizing E_q[log P(x, z | θ)]. Often closed form.

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Convergence

Monotonic increase in likelihood. Converges to local maximum. Random restart or careful init needed.

Applications

Gaussian Mixture Model. Hidden Markov Model. Latent Dirichlet Allocation. Missing data imputation.