Issue No. 09 - September (2005 vol. 27)
Brendan J. Frey , IEEE
Research into methods for reasoning under uncertainty is currently one of the most exciting areas of artificial intelligence, largely because it has recently become possible to record, store, and process large amounts of data. While impressive achievements have been made in pattern classification problems such as handwritten character recognition, face detection, speaker identification, and prediction of gene function, it is even more exciting that researchers are on the verge of introducing systems that can perform large-scale combinatorial analyses of data, decomposing the data into interacting components. For example, computational methods for automatic scene analysis are now emerging in the computer vision community. These methods decompose an input image into its constituent objects, lighting conditions, motion patterns, etc. Two of the main challenges are finding effective representations and models in specific applications and finding efficient algorithms for inference and learning in these models. In this paper, we advocate the use of graph-based probability models and their associated inference and learning algorithms. We review exact techniques and various approximate, computationally efficient techniques, including iterated conditional modes, the expectation maximization (EM) algorithm, Gibbs sampling, the mean field method, variational techniques, structured variational techniques and the sum-product algorithm ("loopy” belief propagation). We describe how each technique can be applied in a vision model of multiple, occluding objects and contrast the behaviors and performances of the techniques using a unifying cost function, free energy.
Index Terms- Graphical models, Bayesian networks, probability models, probabilistic inference, reasoning, learning, Bayesian methods, variational techniques, sum-product algorithm, loopy belief propagation, EM algorithm, mean field, Gibbs sampling, free energy, Gibbs free energy, Bethe free energy.
B. J. Frey and N. Jojic, "A Comparison of Algorithms for Inference and Learning in Probabilistic Graphical Models," in IEEE Transactions on Pattern Analysis & Machine Intelligence, vol. 27, no. , pp. 1392-1416, 2005.