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Convergence of the EM algorithm in KL distance for overspecified Gaussian mixtures

Legg, Alan
Pak, Artur
Melnykov, Igor
Bolatov, Arman
Assylbekov, Zhenisbek
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Abstract
We present a study of the convergence properties of the Expectation-Maximization (EM) algorithm when applied to an overspecified model. In particular, we consider fitting a balanced mixture of two Gaussians to data originating from a single Gaussian. We provide theoretical bounds on the Kullback-Leibler (KL) divergence between the fitted and true distributions. An important feature is concavity and radiality of the expected log-likelihood function on a hypersurface induced by the EM algorithm, which greatly simplifies the analysis. We also show how our result on KL divergence can be used to upperbound the error rate of a mixture discriminant analysis classifier trained by the EM algorithm.
Citation
A. Legg, A. Pak, I. Melnykov, A. Bolatov, and Z. Assylbekov, “Convergence of the EM algorithm in KL distance for overspecified Gaussian mixtures,” Statistical Papers, vol. 66, no. 6, pp. 1–33, Oct. 2025, doi: 10.1007/S00362-025-01749-z
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Statistical Papers
Conference
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Springer Nature
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