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Automorphism Groups of Graphical Models and Lifted Variational Inference
Proceedings of the 29th Conference on Uncertainty in Artificial Intelligence, PMLR R11:55-64, 2013.
Abstract
Using the theory of group action, we first in- troduce the concept of the automorphism group of an exponential family or a graphical model, thus formalizing the general notion of symme- try of a probabilistic model. This automorphism group provides a precise mathematical frame- work for lifted inference in the general exponen- tial family. Its group action partitions the set of random variables and feature functions into equivalent classes (called orbits) having identical marginals and expectations. Then the inference problem is effectively reduced to that of com- puting marginals or expectations for each class, thus avoiding the need to deal with each individ- ual variable or feature. We demonstrate the use- fulness of this general framework in lifting two classes of variational approximation for maxi- mum a posteriori (MAP) inference: local linear programming (LP) relaxation and local LP re- laxation with cycle constraints; the latter yields the first lifted variational inference algorithm that operates on a bound tighter than the local con- straints.