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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.math3.stat.descriptive.summary;
18  
19  import java.io.Serializable;
20  
21  import org.apache.commons.math3.exception.MathIllegalArgumentException;
22  import org.apache.commons.math3.exception.NullArgumentException;
23  import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
24  import org.apache.commons.math3.util.MathUtils;
25  
26  /**
27   * Returns the sum of the squares of the available values.
28   * <p>
29   * If there are no values in the dataset, then 0 is returned.
30   * If any of the values are
31   * <code>NaN</code>, then <code>NaN</code> is returned.</p>
32   * <p>
33   * <strong>Note that this implementation is not synchronized.</strong> If
34   * multiple threads access an instance of this class concurrently, and at least
35   * one of the threads invokes the <code>increment()</code> or
36   * <code>clear()</code> method, it must be synchronized externally.</p>
37   *
38   */
39  public class SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable {
40  
41      /** Serializable version identifier */
42      private static final long serialVersionUID = 1460986908574398008L;
43  
44      /** */
45      private long n;
46  
47      /**
48       * The currently running sumSq
49       */
50      private double value;
51  
52      /**
53       * Create a SumOfSquares instance
54       */
55      public SumOfSquares() {
56          n = 0;
57          value = 0;
58      }
59  
60      /**
61       * Copy constructor, creates a new {@code SumOfSquares} identical
62       * to the {@code original}
63       *
64       * @param original the {@code SumOfSquares} instance to copy
65       * @throws NullArgumentException if original is null
66       */
67      public SumOfSquares(SumOfSquares original) throws NullArgumentException {
68          copy(original, this);
69      }
70  
71      /**
72       * {@inheritDoc}
73       */
74      @Override
75      public void increment(final double d) {
76          value += d * d;
77          n++;
78      }
79  
80      /**
81       * {@inheritDoc}
82       */
83      @Override
84      public double getResult() {
85          return value;
86      }
87  
88      /**
89       * {@inheritDoc}
90       */
91      public long getN() {
92          return n;
93      }
94  
95      /**
96       * {@inheritDoc}
97       */
98      @Override
99      public void clear() {
100         value = 0;
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>MathIllegalArgumentException</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 0 if length = 0
115      * @throws MathIllegalArgumentException 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     throws MathIllegalArgumentException {
121         double sumSq = Double.NaN;
122         if (test(values, begin, length, true)) {
123             sumSq = 0.0;
124             for (int i = begin; i < begin + length; i++) {
125                 sumSq += values[i] * values[i];
126             }
127         }
128         return sumSq;
129     }
130 
131     /**
132      * {@inheritDoc}
133      */
134     @Override
135     public SumOfSquares copy() {
136         SumOfSquares result = new SumOfSquares();
137         // no try-catch or advertised exception here because args are valid
138         copy(this, result);
139         return result;
140     }
141 
142     /**
143      * Copies source to dest.
144      * <p>Neither source nor dest can be null.</p>
145      *
146      * @param source SumOfSquares to copy
147      * @param dest SumOfSquares to copy to
148      * @throws NullArgumentException if either source or dest is null
149      */
150     public static void copy(SumOfSquares source, SumOfSquares dest)
151         throws NullArgumentException {
152         MathUtils.checkNotNull(source);
153         MathUtils.checkNotNull(dest);
154         dest.setData(source.getDataRef());
155         dest.n = source.n;
156         dest.value = source.value;
157     }
158 
159 }