001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.math.matrix;
031
032
033/**
034 * holds an updatable mean vector
035 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
036 */
037public class MeanVector {
038        
039        private double[] mean;
040        private int n;
041
042        /**
043         * 
044         */
045        public MeanVector() {
046                reset();
047        }
048        
049        /**
050         * Update the mean. If no mean currently exists clone the
051         * data as the starting mean
052         * 
053         * @param data
054         * @return update 
055         */
056        public double[] update(double[] data){
057                return update(data,true);
058        }
059        
060        /**
061         * Update the mean. If no mean currently exists copy controls
062         * where the data should be copied or not to initialise mean
063         * 
064         * @param data
065         * @param copy
066         * @return the new mean
067         */
068        public double[] update(double[] data,boolean copy){
069                if(copy) data = data.clone();
070                if(mean == null){
071                        mean = data;
072                        this.n = 1;
073                        return mean;
074                }
075                
076                if(data.length != mean.length){
077                        throw new RuntimeException("Cannot update mean");
078                }
079                
080                for (int i = 0; i < data.length; i++) {
081                        mean[i] = mean[i] + ((data[i] - mean[i])/(n+1));
082                }
083                this.n++;
084                return mean;
085        }
086
087        /**
088         * @return current mean, may be null
089         */
090        public double[] vec() {
091                return this.mean;
092        }
093
094        /**
095         * 
096         */
097        public void reset() {
098                this.mean = null;
099                this.n = 0;
100        }
101
102}