CS228_PS2

CS228_PS2 - CS228 Problem Set #2 1 CS 228, Winter 2011-2012...

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CS228 Problem Set #2 1 CS 228, Winter 2011-2012 Problem Set #2 This assignment is due at 12 noon on Feburary 6. Submissions should be placed in the filing cabinet labeled CS228 Homework Submission Box located in the lobby outside Gates 187 . Suppose we wish to perform exact inference over a chain Markov Random Field given by X 1 - X 2 - ··· - X n . We construct a clique tree of the form C 1 - ··· - C n - 1 where Scope [ C i ] = { X i ,X i +1 } , and calibrate it, resulting in a calibrated clique tree T over unnormalized factors F . Assume that each variable X i has | V al ( X i ) | = d . a) [5 points] Describe how to compute the marginal of a single variable, P Φ ( X i ) for a given X i using the calibrated clique tree. What is the running time cost of this operation? Does the result depend on which clique we use to extract the marginal from? Why? Now, consider the problem of answering a query P ( X 1 ,X 3 ) in our calibrated clique tree. We cannot extract this marginal from any clique in
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This document was uploaded on 01/30/2012.

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CS228_PS2 - CS228 Problem Set #2 1 CS 228, Winter 2011-2012...

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