markovgenerator.java

java实现的隐马尔科夫模型

/* jahmm package - v0.3.1 */

/*
 *  Copyright (c) 2004, Jean-Marc Francois.
 *
 *  This file is part of Jahmm.
 *  Jahmm is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  Jahmm is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with Jahmm; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package be.ac.ulg.montefiore.run.jahmm.toolbox;

import java.util.*;
import be.ac.ulg.montefiore.run.jahmm.*;


/**
 * Generates Markovian observations given a HMM.
 */
public class MarkovGenerator {
    
    private final Hmm hmm;
    private int stateNb;
    

    /**
     * Initializes a Markovian generator.  The generator is ready to generate
     * a new {@link #observation() observation}.
     *
     * @param hmm An Hidden Markov Model that perfectly models the sequences
     *            generated by this object.
     */
    public MarkovGenerator(Hmm hmm) {
	if (hmm == null)
	    throw new IllegalArgumentException();
	
	this.hmm = hmm;
	newSequence();
    }
 
    /**
     * Generates a new (pseudo) random observation.
     *
     * @return The generated observation.
     */
    public Observation observation() {
	Observation o = hmm.getOpdf(stateNb).generate();
	
	double rand = Math.random();

	for (int j = 0; j < hmm.nbStates() - 1; j++)
	    if ((rand -= hmm.getAij(stateNb, j)) < 0) {
		stateNb = j;
		return o;
	    }

	stateNb = hmm.nbStates() - 1;

	return o;
    }
    
    /**
     * Generates a new (pseudo) random observation sequence and start
     * a new one.
     * 
     * @param length The length of the sequence.
     * @return An observation sequence.
     */
    public Vector observationSequence(int length) {
	if (length <= 0)
	    throw new IllegalArgumentException();
	Vector sequence = new Vector();
	
	while (length-- > 0)
	    sequence.add(observation());
	    
	newSequence();
	
	return sequence;
    }

    /**
     * Finds a new state according to the initial (pi) probabilities of each
     * state.
     */
    public void newSequence() {
	double rand = Math.random(), current = 0.;

	for (int i = 0; i < hmm.nbStates() - 1; i++) {
	    current += hmm.getPi(i);

	    if (current > rand) {
		stateNb = i;
		return;
	    }
	}

	stateNb = hmm.nbStates() - 1;
    }

    /**
     * Get the state number of the current state.
     *
     * @return A state number.
     */
    public int stateNb() {
	return stateNb;
    }
}