Lecture 6 : Random Walks versus Independent Sampling
نویسنده
چکیده
For many problems it is necessary to draw samples from some distribution D on a typically large set V . In order to do so, one often considers a Markov chain on V whose limiting distribution is D. The efficiency of the sampling algorithm requires the Markov chain to converge quickly. Two famous examples where this approach have been applied successfully are approximation algorithms for the permanent of nonnegative matrices [SJ89] and for the volume of convex bodies [DFK91]. In this lecture notes, we first see how the convergence of random walks can be related to the second largest eigenvalue of the transition matrix. In the second part, we reveal a more sophisticated property of random walks on expander graphs. Roughly speaking, it turns out that the samples returned by a random walk on an expander of length t are very similar to t independent samples of the vertices of the expander. This property can then be used to reduce the number of required random bits for a broad class of randomized algorithms.
منابع مشابه
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تاریخ انتشار 2011