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 */ 017package org.apache.commons.math4.legacy.stat.descriptive.summary; 018 019import org.apache.commons.math4.legacy.exception.MathIllegalArgumentException; 020import org.apache.commons.math4.legacy.exception.NullArgumentException; 021import org.apache.commons.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic; 022import org.apache.commons.math4.core.jdkmath.JdkMath; 023import org.apache.commons.math4.legacy.core.MathArrays; 024 025/** 026 * Returns the sum of the natural logs for this collection of values. 027 * <p> 028 * Uses {@link org.apache.commons.math4.core.jdkmath.JdkMath#log(double)} to compute the logs. 029 * Therefore, 030 * <ul> 031 * <li>If any of values are < 0, the result is <code>NaN.</code></li> 032 * <li>If all values are non-negative and less than 033 * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the 034 * result is <code>Double.NEGATIVE_INFINITY.</code></li> 035 * <li>If both <code>Double.POSITIVE_INFINITY</code> and 036 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is 037 * <code>NaN.</code></li> 038 * </ul> 039 * <p> 040 * <strong>Note that this implementation is not synchronized.</strong> If 041 * multiple threads access an instance of this class concurrently, and at least 042 * one of the threads invokes the <code>increment()</code> or 043 * <code>clear()</code> method, it must be synchronized externally.</p> 044 */ 045public class SumOfLogs extends AbstractStorelessUnivariateStatistic { 046 /** Number of values that have been added. */ 047 private int n; 048 049 /** 050 * The currently running value. 051 */ 052 private double value; 053 054 /** 055 * Create a SumOfLogs instance. 056 */ 057 public SumOfLogs() { 058 value = 0d; 059 n = 0; 060 } 061 062 /** 063 * Copy constructor, creates a new {@code SumOfLogs} identical 064 * to the {@code original}. 065 * 066 * @param original the {@code SumOfLogs} instance to copy 067 * @throws NullArgumentException if original is null 068 */ 069 public SumOfLogs(SumOfLogs original) throws NullArgumentException { 070 copy(original, this); 071 } 072 073 /** 074 * {@inheritDoc} 075 */ 076 @Override 077 public void increment(final double d) { 078 value += JdkMath.log(d); 079 n++; 080 } 081 082 /** 083 * {@inheritDoc} 084 */ 085 @Override 086 public double getResult() { 087 return value; 088 } 089 090 /** 091 * {@inheritDoc} 092 */ 093 @Override 094 public long getN() { 095 return n; 096 } 097 098 /** 099 * {@inheritDoc} 100 */ 101 @Override 102 public void clear() { 103 value = 0d; 104 n = 0; 105 } 106 107 /** 108 * Returns the sum of the natural logs of the entries in the specified portion of 109 * the input array, or <code>Double.NaN</code> if the designated subarray 110 * is empty. 111 * <p> 112 * Throws <code>MathIllegalArgumentException</code> if the array is null.</p> 113 * <p> 114 * See {@link SumOfLogs}.</p> 115 * 116 * @param values the input array 117 * @param begin index of the first array element to include 118 * @param length the number of elements to include 119 * @return the sum of the natural logs of the values or 0 if 120 * length = 0 121 * @throws MathIllegalArgumentException if the array is null or the array index 122 * parameters are not valid 123 */ 124 @Override 125 public double evaluate(final double[] values, final int begin, final int length) 126 throws MathIllegalArgumentException { 127 128 double sumLog = Double.NaN; 129 if (MathArrays.verifyValues(values, begin, length, true)) { 130 sumLog = 0.0; 131 for (int i = begin; i < begin + length; i++) { 132 sumLog += JdkMath.log(values[i]); 133 } 134 } 135 return sumLog; 136 } 137 138 /** 139 * {@inheritDoc} 140 */ 141 @Override 142 public SumOfLogs copy() { 143 SumOfLogs result = new SumOfLogs(); 144 // No try-catch or advertised exception here because args are valid 145 copy(this, result); 146 return result; 147 } 148 149 /** 150 * Copies source to dest. 151 * <p>Neither source nor dest can be null.</p> 152 * 153 * @param source SumOfLogs to copy 154 * @param dest SumOfLogs to copy to 155 * @throws NullArgumentException if either source or dest is null 156 */ 157 public static void copy(SumOfLogs source, SumOfLogs dest) 158 throws NullArgumentException { 159 NullArgumentException.check(source); 160 NullArgumentException.check(dest); 161 dest.n = source.n; 162 dest.value = source.value; 163 } 164}