Uncertainty in Artificial Intelligence
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Computational Complexity Reduction for BN2O Networks Using Similarity of States
Alexander Kozlov, Jaswinder Singh
Although probabilistic inference in a general Bayesian belief network is an NP-hard problem, computation time for inference can be reduced in most practical cases by exploiting domain knowledge and by making approximations in the knowledge representation. In this paper we introduce the property of similarity of states and a new method for approximate knowledge representation and inference which is based on this property. We define two or more states of a node to be similar when the ratio of their probabilities, the likelihood ratio, does not depend on the instantiations of the other nodes in the network. We show that the similarity of states exposes redundancies in the joint probability distribution which can be exploited to reduce the computation time of probabilistic inference in networks with multiple similar states, and that the computational complexity in the networks with exponentially many similar states might be polynomial. We demonstrate our ideas on the example of a BN2O networkóa two layer network often used in diagnostic problemsóby reducing it to a very close network with multiple similar states. We show that the answers to practical queries converge very fast to the answers obtained with the original network. The maximum error is as low as 5% for models that require only 10% of the computation time needed by the original BN2O model.
Keywords: Probabilistic inference, approximate probabilistic inference, similarity networks, B
Pages: 357-364
PS Link: http://www.stanford.edu/~alexvk/PAPERS/similarity-uai-96.ps
PDF Link: /papers/96/p357-kozlov.pdf
AUTHOR = "Alexander Kozlov and Jaswinder Singh",
TITLE = "Computational Complexity Reduction for BN2O Networks Using Similarity of States",
BOOKTITLE = "Proceedings of the Twelfth Conference Annual Conference on Uncertainty in Artificial Intelligence (UAI-96)",
PUBLISHER = "Morgan Kaufmann",
ADDRESS = "San Francisco, CA",
YEAR = "1996",
PAGES = "357--364"

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