2018

Singularity, Misspecification, and the Convergence Rate of EM

Dwivedi, Raaz, Ho, Nhat, Khamaru, Koulik et al.

Understand

A line of recent work has analyzed the behavior of the Expectation-Maximization (EM) algorithm in the well-specified setting, in which the population likelihood is locally strongly concave around its maximizing argument.

  • Examples include suitably separated Gaussian mixture models and mixtures of linear regressions.
  • We consider over-specified settings in which the number of fitted components is larger than the number of components in the true distribution.
  • Such misspecified settings can lead to singularity in the Fisher information matrix, and moreover, the maximum likelihood estimator based on $n$ i.i.d.

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