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.summary; 018 019 import java.io.Serializable; 020 021 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; 022 023 /** 024 * Returns the sum of the squares of the available values. 025 * <p> 026 * If there are no values in the dataset, or any of the values are 027 * <code>NaN</code>, then <code>NaN</code> is returned.</p> 028 * <p> 029 * <strong>Note that this implementation is not synchronized.</strong> If 030 * multiple threads access an instance of this class concurrently, and at least 031 * one of the threads invokes the <code>increment()</code> or 032 * <code>clear()</code> method, it must be synchronized externally.</p> 033 * 034 * @version $Revision: 762087 $ $Date: 2009-04-05 10:20:18 -0400 (Sun, 05 Apr 2009) $ 035 */ 036 public class SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable { 037 038 /** Serializable version identifier */ 039 private static final long serialVersionUID = 1460986908574398008L; 040 041 /** */ 042 private long n; 043 044 /** 045 * The currently running sumSq 046 */ 047 private double value; 048 049 /** 050 * Create a SumOfSquares instance 051 */ 052 public SumOfSquares() { 053 n = 0; 054 value = Double.NaN; 055 } 056 057 /** 058 * Copy constructor, creates a new {@code SumOfSquares} identical 059 * to the {@code original} 060 * 061 * @param original the {@code SumOfSquares} instance to copy 062 */ 063 public SumOfSquares(SumOfSquares original) { 064 copy(original, this); 065 } 066 067 /** 068 * {@inheritDoc} 069 */ 070 @Override 071 public void increment(final double d) { 072 if (n == 0) { 073 value = d * d; 074 } else { 075 value += d * d; 076 } 077 n++; 078 } 079 080 /** 081 * {@inheritDoc} 082 */ 083 @Override 084 public double getResult() { 085 return value; 086 } 087 088 /** 089 * {@inheritDoc} 090 */ 091 public long getN() { 092 return n; 093 } 094 095 /** 096 * {@inheritDoc} 097 */ 098 @Override 099 public void clear() { 100 value = Double.NaN; 101 n = 0; 102 } 103 104 /** 105 * Returns the sum of the squares of the entries in the specified portion of 106 * the input array, or <code>Double.NaN</code> if the designated subarray 107 * is empty. 108 * <p> 109 * Throws <code>IllegalArgumentException</code> if the array is null.</p> 110 * 111 * @param values the input array 112 * @param begin index of the first array element to include 113 * @param length the number of elements to include 114 * @return the sum of the squares of the values or Double.NaN if length = 0 115 * @throws IllegalArgumentException if the array is null or the array index 116 * parameters are not valid 117 */ 118 @Override 119 public double evaluate(final double[] values,final int begin, final int length) { 120 double sumSq = Double.NaN; 121 if (test(values, begin, length)) { 122 sumSq = 0.0; 123 for (int i = begin; i < begin + length; i++) { 124 sumSq += values[i] * values[i]; 125 } 126 } 127 return sumSq; 128 } 129 130 /** 131 * {@inheritDoc} 132 */ 133 @Override 134 public SumOfSquares copy() { 135 SumOfSquares result = new SumOfSquares(); 136 copy(this, result); 137 return result; 138 } 139 140 /** 141 * Copies source to dest. 142 * <p>Neither source nor dest can be null.</p> 143 * 144 * @param source SumOfSquares to copy 145 * @param dest SumOfSquares to copy to 146 * @throws NullPointerException if either source or dest is null 147 */ 148 public static void copy(SumOfSquares source, SumOfSquares dest) { 149 dest.n = source.n; 150 dest.value = source.value; 151 } 152 153 }