001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.math.stat.descriptive.moment; 018 019 import java.io.Serializable; 020 021 import org.apache.commons.math.MathRuntimeException; 022 import org.apache.commons.math.exception.util.LocalizedFormats; 023 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; 024 import org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic; 025 import org.apache.commons.math.stat.descriptive.summary.SumOfLogs; 026 import org.apache.commons.math.util.FastMath; 027 028 /** 029 * Returns the <a href="http://www.xycoon.com/geometric_mean.htm"> 030 * geometric mean </a> of the available values. 031 * <p> 032 * Uses a {@link SumOfLogs} instance to compute sum of logs and returns 033 * <code> exp( 1/n (sum of logs) ).</code> Therefore, </p> 034 * <ul> 035 * <li>If any of values are < 0, the result is <code>NaN.</code></li> 036 * <li>If all values are non-negative and less than 037 * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the 038 * result is <code>0.</code></li> 039 * <li>If both <code>Double.POSITIVE_INFINITY</code> and 040 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is 041 * <code>NaN.</code></li> 042 * </ul> </p> 043 * <p> 044 * <strong>Note that this implementation is not synchronized.</strong> If 045 * multiple threads access an instance of this class concurrently, and at least 046 * one of the threads invokes the <code>increment()</code> or 047 * <code>clear()</code> method, it must be synchronized externally.</p> 048 * 049 * 050 * @version $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $ 051 */ 052 public class GeometricMean extends AbstractStorelessUnivariateStatistic implements Serializable { 053 054 /** Serializable version identifier */ 055 private static final long serialVersionUID = -8178734905303459453L; 056 057 /** Wrapped SumOfLogs instance */ 058 private StorelessUnivariateStatistic sumOfLogs; 059 060 /** 061 * Create a GeometricMean instance 062 */ 063 public GeometricMean() { 064 sumOfLogs = new SumOfLogs(); 065 } 066 067 /** 068 * Copy constructor, creates a new {@code GeometricMean} identical 069 * to the {@code original} 070 * 071 * @param original the {@code GeometricMean} instance to copy 072 */ 073 public GeometricMean(GeometricMean original) { 074 super(); 075 copy(original, this); 076 } 077 078 /** 079 * Create a GeometricMean instance using the given SumOfLogs instance 080 * @param sumOfLogs sum of logs instance to use for computation 081 */ 082 public GeometricMean(SumOfLogs sumOfLogs) { 083 this.sumOfLogs = sumOfLogs; 084 } 085 086 /** 087 * {@inheritDoc} 088 */ 089 @Override 090 public GeometricMean copy() { 091 GeometricMean result = new GeometricMean(); 092 copy(this, result); 093 return result; 094 } 095 096 /** 097 * {@inheritDoc} 098 */ 099 @Override 100 public void increment(final double d) { 101 sumOfLogs.increment(d); 102 } 103 104 /** 105 * {@inheritDoc} 106 */ 107 @Override 108 public double getResult() { 109 if (sumOfLogs.getN() > 0) { 110 return FastMath.exp(sumOfLogs.getResult() / sumOfLogs.getN()); 111 } else { 112 return Double.NaN; 113 } 114 } 115 116 /** 117 * {@inheritDoc} 118 */ 119 @Override 120 public void clear() { 121 sumOfLogs.clear(); 122 } 123 124 /** 125 * Returns the geometric mean of the entries in the specified portion 126 * of the input array. 127 * <p> 128 * See {@link GeometricMean} for details on the computing algorithm.</p> 129 * <p> 130 * Throws <code>IllegalArgumentException</code> if the array is null.</p> 131 * 132 * @param values input array containing the values 133 * @param begin first array element to include 134 * @param length the number of elements to include 135 * @return the geometric mean or Double.NaN if length = 0 or 136 * any of the values are <= 0. 137 * @throws IllegalArgumentException if the input array is null or the array 138 * index parameters are not valid 139 */ 140 @Override 141 public double evaluate( 142 final double[] values, final int begin, final int length) { 143 return FastMath.exp( 144 sumOfLogs.evaluate(values, begin, length) / length); 145 } 146 147 /** 148 * {@inheritDoc} 149 */ 150 public long getN() { 151 return sumOfLogs.getN(); 152 } 153 154 /** 155 * <p>Sets the implementation for the sum of logs.</p> 156 * <p>This method must be activated before any data has been added - i.e., 157 * before {@link #increment(double) increment} has been used to add data; 158 * otherwise an IllegalStateException will be thrown.</p> 159 * 160 * @param sumLogImpl the StorelessUnivariateStatistic instance to use 161 * for computing the log sum 162 * @throws IllegalStateException if data has already been added 163 * (i.e if n > 0) 164 */ 165 public void setSumLogImpl( 166 StorelessUnivariateStatistic sumLogImpl) { 167 checkEmpty(); 168 this.sumOfLogs = sumLogImpl; 169 } 170 171 /** 172 * Returns the currently configured sum of logs implementation 173 * 174 * @return the StorelessUnivariateStatistic implementing the log sum 175 */ 176 public StorelessUnivariateStatistic getSumLogImpl() { 177 return sumOfLogs; 178 } 179 180 /** 181 * Copies source to dest. 182 * <p>Neither source nor dest can be null.</p> 183 * 184 * @param source GeometricMean to copy 185 * @param dest GeometricMean to copy to 186 * @throws NullPointerException if either source or dest is null 187 */ 188 public static void copy(GeometricMean source, GeometricMean dest) { 189 dest.setData(source.getDataRef()); 190 dest.sumOfLogs = source.sumOfLogs.copy(); 191 } 192 193 194 /** 195 * Throws IllegalStateException if n > 0. 196 */ 197 private void checkEmpty() { 198 if (getN() > 0) { 199 throw MathRuntimeException.createIllegalStateException( 200 LocalizedFormats.VALUES_ADDED_BEFORE_CONFIGURING_STATISTIC, 201 getN()); 202 } 203 } 204 205 }