6 research outputs found
Dynamic Inference in Probabilistic Graphical Models
Probabilistic graphical models, such as Markov random fields (MRFs), are
useful for describing high-dimensional distributions in terms of local
dependence structures. The probabilistic inference is a fundamental problem
related to graphical models, and sampling is a main approach for the problem.
In this paper, we study probabilistic inference problems when the graphical
model itself is changing dynamically with time. Such dynamic inference problems
arise naturally in today's application, e.g.~multivariate time-series data
analysis and practical learning procedures.
We give a dynamic algorithm for sampling-based probabilistic inferences in
MRFs, where each dynamic update can change the underlying graph and all
parameters of the MRF simultaneously, as long as the total amount of changes is
bounded. More precisely, suppose that the MRF has variables and
polylogarithmic-bounded maximum degree, and independent samples are
sufficient for the inference for a polynomial function . Our
algorithm dynamically maintains an answer to the inference problem using
space cost, and incremental
time cost upon each update to the MRF, as long as the well-known
Dobrushin-Shlosman condition is satisfied by the MRFs. Compared to the static
case, which requires time cost for redrawing all
samples whenever the MRF changes, our dynamic algorithm gives a
-factor speedup. Our approach relies on a
novel dynamic sampling technique, which transforms local Markov chains (a.k.a.
single-site dynamics) to dynamic sampling algorithms, and an "algorithmic
Lipschitz" condition that we establish for sampling from graphical models,
namely, when the MRF changes by a small difference, samples can be modified to
reflect the new distribution, with cost proportional to the difference on MRF
Fundamentals of Partial Rejection Sampling
Partial Rejection Sampling is an algorithmic approach to obtaining a perfect
sample from a specified distribution. The objects to be sampled are assumed to
be represented by a number of random variables. In contrast to classical
rejection sampling, in which all variables are resampled until a feasible
solution is found, partial rejection sampling aims at greater efficiency by
resampling only a subset of variables that `go wrong'. Partial rejection
sampling is closely related to Moser and Tardos' algorithmic version of the
Lov\'asz Local Lemma, but with the additional requirement that a specified
output distribution should be met. This article provides a largely
self-contained account of the basic form of the algorithm and its analysis
Perfect sampling from spatial mixing
We introduce a new perfect sampling technique that can be applied to general Gibbs distributions and runs in linear time if the correlation decays faster than the neighborhood growth. In particular, in graphs with subexponential neighborhood growth like [Formula: see text] , our algorithm achieves linear running time as long as Gibbs sampling is rapidly mixing. As concrete applications, we obtain the currently best perfect samplers for colorings and for monomerâdimer models in such graphs