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/* * wiigee - accelerometerbased gesture recognition * Copyright (C) 2007, 2008, 2009 Benjamin Poppinga * //w w w. ja v a 2s . c o m * Developed at University of Oldenburg * Contact: wiigee@benjaminpoppinga.de * * This file is part of wiigee. * * wiigee is free software; you can redistribute it and/or modify * it under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program 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 Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public License along * with this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. */ package org.wiigee.logic; import java.text.DecimalFormat; import java.util.Vector; import org.wiigee.util.Log; /** * This is a Hidden Markov Model implementation which internally provides * the basic algorithms for training and recognition (forward and backward * algorithm). Since a regular Hidden Markov Model doesn't provide a possibility * to train multiple sequences, this implementation has been optimized for this * purposes using some state-of-the-art technologies described in several papers. * * @author Benjamin 'BePo' Poppinga * */ public class HMM { /** The number of states */ protected int numStates; /** The number of observations */ protected int numObservations; /** The initial probabilities for each state: p[state] */ protected double pi[]; /** The state change probability to switch from state A to * state B: a[stateA][stateB] */ protected double a[][]; /** The probability to emit symbol S in state A: b[stateA][symbolS] */ protected double b[][]; /** * Initialize the Hidden Markov Model in a left-to-right version. * * @param numStates Number of states * @param numObservations Number of observations */ public HMM(int numStates, int numObservations) { this.numStates = numStates; this.numObservations = numObservations; pi = new double[numStates]; a = new double[numStates][numStates]; b = new double[numStates][numObservations]; this.reset(); } /** * Reset the Hidden Markov Model to the initial left-to-right values. * */ private void reset() { int jumplimit = 2; // set startup probability pi[0] = 1; for(int i=1; i<numStates; i++) { pi[i] = 0; } // set state change probabilities in the left-to-right version // NOTE: i now that this is dirty and very static. :) for(int i=0; i<numStates; i++) { for(int j=0; j<numStates; j++) { if(i==numStates-1 && j==numStates-1) { // last row a[i][j] = 1.0; } else if(i==numStates-2 && j==numStates-2) { // next to last row a[i][j] = 0.5; } else if(i==numStates-2 && j==numStates-1) { // next to last row a[i][j] = 0.5; } else if(i<=j && i>j-jumplimit-1) { a[i][j] = 1.0/(jumplimit+1); } else { a[i][j] = 0.0; } } } // emission probability for(int i=0; i<numStates; i++) { for(int j=0; j<numObservations; j++) { b[i][j] = 1.0/(double)numObservations; } } } /** * Trains the Hidden Markov Model with multiple sequences. * This method is normally not known to basic hidden markov * models, because they usually use the Baum-Welch-Algorithm. * This method is NOT the traditional Baum-Welch-Algorithm. * * If you want to know in detail how it works please consider * my Individuelles Projekt paper on the wiigee Homepage. Also * there exist some english literature on the world wide web. * Try to search for some papers by Rabiner or have a look at * Vesa-Matti Mntyl - "Discrete Hidden Markov Models with * application to isolated user-dependent hand gesture recognition". * */ public void train(Vector<int[]> trainsequence) { double[][] a_new = new double[a.length][a.length]; double[][] b_new = new double[b.length][b[0].length]; // re calculate state change probability a for(int i=0; i<a.length; i++) { for(int j=0; j<a[i].length; j++) { double zaehler=0; double nenner=0; for(int k=0; k<trainsequence.size(); k++) { int[] sequence = trainsequence.elementAt(k); double[][] fwd = this.forwardProc(sequence); double[][] bwd = this.backwardProc(sequence); double prob = this.getProbability(sequence); double zaehler_innersum=0; double nenner_innersum=0; for(int t=0; t<sequence.length-1; t++) { zaehler_innersum+=fwd[i][t]*a[i][j]*b[j][sequence[t+1]]*bwd[j][t+1]; nenner_innersum+=fwd[i][t]*bwd[i][t]; } zaehler+=(1/prob)*zaehler_innersum; nenner+=(1/prob)*nenner_innersum; } // k a_new[i][j] = zaehler/nenner; } // j } // i // re calculate emission probability b for(int i=0; i<b.length; i++) { // zustaende for(int j=0; j<b[i].length; j++) { // symbole double zaehler=0; double nenner=0; for(int k=0; k<trainsequence.size(); k++) { int[] sequence = trainsequence.elementAt(k); double[][] fwd = this.forwardProc(sequence); double[][] bwd = this.backwardProc(sequence); double prob = this.getProbability(sequence); double zaehler_innersum=0; double nenner_innersum=0; for(int t=0; t<sequence.length-1; t++) { if(sequence[t]==j) { zaehler_innersum+=fwd[i][t]*bwd[i][t]; } nenner_innersum+=fwd[i][t]*bwd[i][t]; } zaehler+=(1/prob)*zaehler_innersum; nenner+=(1/prob)*nenner_innersum; } // k b_new[i][j] = zaehler/nenner; } // j } // i this.a=a_new; this.b=b_new; } /** * Traditional Forward Algorithm. * * @param o the observationsequence O * @return Array[State][Time] * */ protected double[][] forwardProc(int[] o) { double[][] f = new double[numStates][o.length]; for (int l = 0; l < f.length; l++) { f[l][0] = pi[l] * b[l][o[0]]; } for (int i = 1; i < o.length; i++) { for (int k = 0; k < f.length; k++) { double sum = 0; for (int l = 0; l < numStates; l++) { sum += f[l][i-1] * a[l][k]; } f[k][i] = sum * b[k][o[i]]; } } return f; } /** * Returns the probability that a observation sequence O belongs * to this Hidden Markov Model without using the bayes classifier. * Internally the well known forward algorithm is used. * * @param o observation sequence * @return probability that sequence o belongs to this hmm */ public double getProbability(int[] o) { double prob = 0.0; double[][] forward = this.forwardProc(o); // add probabilities for (int i = 0; i < forward.length; i++) { // for every state prob += forward[i][forward[i].length - 1]; } return prob; } /** * Backward algorithm. * * @param o observation sequence o * @return Array[State][Time] */ protected double[][] backwardProc(int[] o) { int T = o.length; double[][] bwd = new double[numStates][T]; /* Basisfall */ for (int i = 0; i < numStates; i++) bwd[i][T - 1] = 1; /* Induktion */ for (int t = T - 2; t >= 0; t--) { for (int i = 0; i < numStates; i++) { bwd[i][t] = 0; for (int j = 0; j < numStates; j++) bwd[i][t] += (bwd[j][t + 1] * a[i][j] * b[j][o[t + 1]]); } } return bwd; } /** * Prints everything about this model, including * all values. For debug purposes or if you want * to comprehend what happend to the model. * */ public void print() { DecimalFormat fmt = new DecimalFormat(); fmt.setMinimumFractionDigits(5); fmt.setMaximumFractionDigits(5); for (int i = 0; i < numStates; i++) Log.write("pi(" + i + ") = " + fmt.format(pi[i])); Log.write(""); for (int i = 0; i < numStates; i++) { for (int j = 0; j < numStates; j++) Log.write("a(" + i + "," + j + ") = " + fmt.format(a[i][j]) + " "); Log.write(""); } Log.write(""); for (int i = 0; i < numStates; i++) { for (int k = 0; k < numObservations; k++) Log.write("b(" + i + "," + k + ") = " + fmt.format(b[i][k]) + " "); Log.write(""); } } public double[] getPi() { return this.pi; } public void setPi(double[] pi) { this.pi = pi; } public double[][] getA() { return this.a; } public void setA(double[][] a) { this.a = a; } public double[][] getB() { return this.b; } public void setB(double[][] b) { this.b=b; } }