1 /* 2 * Copyright 2003-2004 The Apache Software Foundation. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 package org.apache.commons.math.stat.descriptive.summary; 17 18 import java.io.Serializable; 19 20 import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; 21 22 /** 23 * Returns the sum of the squares of the available values. 24 * <p> 25 * If there are no values in the dataset, or any of the values are 26 * <code>NaN</code>, then <code>NaN</code> is returned. 27 * <p> 28 * <strong>Note that this implementation is not synchronized.</strong> If 29 * multiple threads access an instance of this class concurrently, and at least 30 * one of the threads invokes the <code>increment()</code> or 31 * <code>clear()</code> method, it must be synchronized externally. 32 * 33 * @version $Revision: 348519 $ $Date: 2005-11-23 12:12:18 -0700 (Wed, 23 Nov 2005) $ 34 */ 35 public class SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable { 36 37 /** Serializable version identifier */ 38 private static final long serialVersionUID = 1460986908574398008L; 39 40 /** */ 41 private long n; 42 43 /** 44 * The currently running sumSq 45 */ 46 private double value; 47 48 /** 49 * Create a SumOfSquares instance 50 */ 51 public SumOfSquares() { 52 n = 0; 53 value = Double.NaN; 54 } 55 56 /** 57 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#increment(double) 58 */ 59 public void increment(final double d) { 60 if (n == 0) { 61 value = d * d; 62 } else { 63 value += d * d; 64 } 65 n++; 66 } 67 68 /** 69 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getResult() 70 */ 71 public double getResult() { 72 return value; 73 } 74 75 /** 76 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getN() 77 */ 78 public long getN() { 79 return n; 80 } 81 82 /** 83 * @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#clear() 84 */ 85 public void clear() { 86 value = Double.NaN; 87 n = 0; 88 } 89 90 /** 91 * Returns the sum of the squares of the entries in the specified portion of 92 * the input array, or <code>Double.NaN</code> if the designated subarray 93 * is empty. 94 * <p> 95 * Throws <code>IllegalArgumentException</code> if the array is null. 96 * 97 * @param values the input array 98 * @param begin index of the first array element to include 99 * @param length the number of elements to include 100 * @return the sum of the squares of the values or Double.NaN if length = 0 101 * @throws IllegalArgumentException if the array is null or the array index 102 * parameters are not valid 103 */ 104 public double evaluate(final double[] values,final int begin, final int length) { 105 double sumSq = Double.NaN; 106 if (test(values, begin, length)) { 107 sumSq = 0.0; 108 for (int i = begin; i < begin + length; i++) { 109 sumSq += values[i] * values[i]; 110 } 111 } 112 return sumSq; 113 } 114 115 }