Local Maxima in the Likelihood of Gaussian Mixture Models: Structural Results and Algorithmic Consequences
نویسندگان
چکیده
We provide two fundamental results on the population (infinite-sample) likelihood function of Gaussian mixture models with M ≥ 3 components. Our first main result shows that the population likelihood function has bad local maxima even in the special case of equally-weighted mixtures of well-separated and spherical Gaussians. We prove that the log-likelihood value of these bad local maxima can be arbitrarily worse than that of any global optimum, thereby resolving an open question of Srebro [2007]. Our second main result shows that the EM algorithm (or a first-order variant of it) with random initialization will converge to bad critical points with probability at least 1− e−Ω(M). We further establish that a first-order variant of EM will not converge to strict saddle points almost surely, indicating that the poor performance of the first-order method can be attributed to the existence of bad local maxima rather than bad saddle points. Overall, our results highlight the necessity of careful initialization when using the EM algorithm in practice, even when applied in highly favorable settings.
منابع مشابه
Spoken Language Identification for Indian Languages Using Split and Merge EM Algorithm
Performance of Language Identification (LID) System using Gaussian Mixture Models (GMM) is limited by the convergence of Expectation Maximization (EM) algorithm to local maxima. In this paper an LID system is described using Gaussian Mixture Models for the extracted features which are then trained using Split and Merge Expectation Maximization Algorithm that improves the global convergence of E...
متن کاملA Note on the Article ’ Inference for multivariate normal mixtures ’
Gaussian mixture models provide a flexible tool for data modeling, clustering and classification. We consider the problem of estimating the parameters of a multivariate Gaussian mixture with K components by maximizing the likelihood function. This approach has a theoretical drawback: the likelihood function is unbounded, and the interesting maxima are local maxima in the interior of the paramet...
متن کاملSplit and Merge EM Algorithm for Improving Gaussian Mixture Density Estimates
The EM algorithm for Gaussian mixture models often gets caught in local maxima of the likelihood which involve having too many Gaussians in one part of the space and too few in another, widely separated part of the space. We present a new EM algorithm which performs split and merge operations on the Gaussians to escape from these configurations. This algorithm uses two novel criteria for effici...
متن کاملCritical Lines in Symmetry of Mixture Models and its Application to Component Splitting
We show the existence of critical points as lines for the likelihood function of mixture-type models. They are given by embedding of a critical point for models with less components. A sufficient condition that the critical line gives local maxima or saddle points is also derived. Based on this fact, a component-split method is proposed for a mixture of Gaussian components, and its effectivenes...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2016