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 }