1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.math.stat.descriptive.summary; 18 19 import java.io.Serializable; 20 21 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; 22 23 /** 24 * Returns the sum of the natural logs for this collection of values. 25 * <p> 26 * Uses {@link java.lang.Math#log(double)} to compute the logs. Therefore, 27 * <ul> 28 * <li>If any of values are < 0, the result is <code>NaN.</code></li> 29 * <li>If all values are non-negative and less than 30 * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the 31 * result is <code>Double.NEGATIVE_INFINITY.</code></li> 32 * <li>If both <code>Double.POSITIVE_INFINITY</code> and 33 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is 34 * <code>NaN.</code></li> 35 * </ul></p> 36 * <p> 37 * <strong>Note that this implementation is not synchronized.</strong> If 38 * multiple threads access an instance of this class concurrently, and at least 39 * one of the threads invokes the <code>increment()</code> or 40 * <code>clear()</code> method, it must be synchronized externally.</p> 41 * 42 * @version $Revision: 762087 $ $Date: 2009-04-05 10:20:18 -0400 (Sun, 05 Apr 2009) $ 43 */ 44 public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements Serializable { 45 46 /** Serializable version identifier */ 47 private static final long serialVersionUID = -370076995648386763L; 48 49 /**Number of values that have been added */ 50 private int n; 51 52 /** 53 * The currently running value 54 */ 55 private double value; 56 57 /** 58 * Create a SumOfLogs instance 59 */ 60 public SumOfLogs() { 61 value = 0d; 62 n = 0; 63 } 64 65 /** 66 * Copy constructor, creates a new {@code SumOfLogs} identical 67 * to the {@code original} 68 * 69 * @param original the {@code SumOfLogs} instance to copy 70 */ 71 public SumOfLogs(SumOfLogs original) { 72 copy(original, this); 73 } 74 75 /** 76 * {@inheritDoc} 77 */ 78 @Override 79 public void increment(final double d) { 80 value += Math.log(d); 81 n++; 82 } 83 84 /** 85 * {@inheritDoc} 86 */ 87 @Override 88 public double getResult() { 89 if (n > 0) { 90 return value; 91 } else { 92 return Double.NaN; 93 } 94 } 95 96 /** 97 * {@inheritDoc} 98 */ 99 public long getN() { 100 return n; 101 } 102 103 /** 104 * {@inheritDoc} 105 */ 106 @Override 107 public void clear() { 108 value = 0d; 109 n = 0; 110 } 111 112 /** 113 * Returns the sum of the natural logs of the entries in the specified portion of 114 * the input array, or <code>Double.NaN</code> if the designated subarray 115 * is empty. 116 * <p> 117 * Throws <code>IllegalArgumentException</code> if the array is null.</p> 118 * <p> 119 * See {@link SumOfLogs}.</p> 120 * 121 * @param values the input array 122 * @param begin index of the first array element to include 123 * @param length the number of elements to include 124 * @return the sum of the natural logs of the values or Double.NaN if 125 * length = 0 126 * @throws IllegalArgumentException if the array is null or the array index 127 * parameters are not valid 128 */ 129 @Override 130 public double evaluate(final double[] values, final int begin, final int length) { 131 double sumLog = Double.NaN; 132 if (test(values, begin, length)) { 133 sumLog = 0.0; 134 for (int i = begin; i < begin + length; i++) { 135 sumLog += Math.log(values[i]); 136 } 137 } 138 return sumLog; 139 } 140 141 /** 142 * {@inheritDoc} 143 */ 144 @Override 145 public SumOfLogs copy() { 146 SumOfLogs result = new SumOfLogs(); 147 copy(this, result); 148 return result; 149 } 150 151 /** 152 * Copies source to dest. 153 * <p>Neither source nor dest can be null.</p> 154 * 155 * @param source SumOfLogs to copy 156 * @param dest SumOfLogs to copy to 157 * @throws NullPointerException if either source or dest is null 158 */ 159 public static void copy(SumOfLogs source, SumOfLogs dest) { 160 dest.n = source.n; 161 dest.value = source.value; 162 } 163 }