viterbitrp.java

这是一个matlab的java实现。里面有许多内容。请大家慢慢捉摸。

/* Copyright (C) 2003 Univ. of Massachusetts Amherst, Computer Science Dept.
   This file is part of "MALLET" (MAchine Learning for LanguagE Toolkit).
   http://www.cs.umass.edu/~mccallum/mallet
   This software is provided under the terms of the Common Public License,
   version 1.0, as published by http://www.opensource.org.  For further
   information, see the file `LICENSE' included with this distribution. */

package edu.umass.cs.mallet.grmm;

import java.util.logging.Logger;
import edu.umass.cs.mallet.base.util.MalletLogger;




/**
 *  *
 * Created: Tue Jan 13 18:57:01 2004
 *
 * @author <a href="mailto:[e-mail]">Charles Sutton</a>
 * @version $Id: ViterbiTRP.java,v 1.1 2004/07/15 17:53:31 casutton Exp $
 */
public class ViterbiTRP extends TRP {

	private static Logger logger = MalletLogger.getLogger (ViterbiTRP.class.getName());

	public ViterbiTRP () 
	{
		this (null, null);
	}

	public ViterbiTRP (TRP.TreeFactory f) 
	{
		this (f, null);
	}

	public ViterbiTRP (TRP.TreeFactory f, TRP.TerminationCondition cond) 
	{
		super (f, cond);
		normalizeBeliefs = false;
    inLogSpace = true;
	}

	public double lookupJoint (Assignment assn)
	{
		throw new UnsupportedOperationException
			("ViterbiTRP cannot compute factorized joints.");
	}

	public double lookupLogJoint (Assignment assn)
	{
		throw new UnsupportedOperationException
			("ViterbiTRP cannot compute factorized joints.");
	}

	// copy-paste from ViterbiPropagation

	protected void sendMessage (UndirectedModel mdl, Variable from, Variable to)
	{
//		logger.fine ("ViterbiTRP sending message "+from+" --> "+to);

		int fromIdx = mdl.getIndex (from);
		int toIdx = mdl.getIndex (to);

    DiscretePotential product = mdl.potentialOfEdge (from, to).duplicate();
    if (inLogSpace) product.logify();
    msgProduct (product, fromIdx, toIdx);

		DiscretePotential msg = product.extractMax (to);
		msg.normalize();

		assert msg.varSet().size() == 1 : 
  		"Error in message from "+from+" to "+to+": varSet too big: "+msg;
		assert msg.varSet().contains (to) :
			"Error in message from "+from+" to "+to+"\n  potential "+msg
				+ "does not contain "+to;

		messages[toIdx][fromIdx] = msg;	
//    System.out.println ("Message "+from+" --> "+to+" was: "+msg);
	}

	protected DiscretePotential msgProduct (DiscretePotential product, int idx, int excludeMsgFrom)
	{
    if (product == null) {
      product = new MultinomialPotential(mdlCurrent.get(idx));
    }
		if (inLogSpace) product.logify ();
		for (int j = 0; j < messages[idx].length; j++) {
			if ((messages[idx][j] != null) && (j != excludeMsgFrom)) {
				product.multiplyBy (messages [idx][j]);
			}
		}
//		logger.finest ("msgProduct returned "+sum);
		return product;
	}

	protected DiscretePotential lookupMarginal (UndirectedModel mdl, Variable var)
	{
		DiscretePotential ptl = super.lookupMarginal (mdl, var);
		return ptl;
	}

}