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.math3.stat.descriptive.summary;
018    
019    import java.io.Serializable;
020    
021    import org.apache.commons.math3.exception.MathIllegalArgumentException;
022    import org.apache.commons.math3.exception.NullArgumentException;
023    import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
024    import org.apache.commons.math3.util.MathUtils;
025    
026    /**
027     * Returns the sum of the squares of the available values.
028     * <p>
029     * If there are no values in the dataset, then 0 is returned.
030     * If any of the values are
031     * <code>NaN</code>, then <code>NaN</code> is returned.</p>
032     * <p>
033     * <strong>Note that this implementation is not synchronized.</strong> If
034     * multiple threads access an instance of this class concurrently, and at least
035     * one of the threads invokes the <code>increment()</code> or
036     * <code>clear()</code> method, it must be synchronized externally.</p>
037     *
038     * @version $Id: SumOfSquares.java 1416643 2012-12-03 19:37:14Z tn $
039     */
040    public class SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable {
041    
042        /** Serializable version identifier */
043        private static final long serialVersionUID = 1460986908574398008L;
044    
045        /** */
046        private long n;
047    
048        /**
049         * The currently running sumSq
050         */
051        private double value;
052    
053        /**
054         * Create a SumOfSquares instance
055         */
056        public SumOfSquares() {
057            n = 0;
058            value = 0;
059        }
060    
061        /**
062         * Copy constructor, creates a new {@code SumOfSquares} identical
063         * to the {@code original}
064         *
065         * @param original the {@code SumOfSquares} instance to copy
066         * @throws NullArgumentException if original is null
067         */
068        public SumOfSquares(SumOfSquares original) throws NullArgumentException {
069            copy(original, this);
070        }
071    
072        /**
073         * {@inheritDoc}
074         */
075        @Override
076        public void increment(final double d) {
077            value += d * d;
078            n++;
079        }
080    
081        /**
082         * {@inheritDoc}
083         */
084        @Override
085        public double getResult() {
086            return value;
087        }
088    
089        /**
090         * {@inheritDoc}
091         */
092        public long getN() {
093            return n;
094        }
095    
096        /**
097         * {@inheritDoc}
098         */
099        @Override
100        public void clear() {
101            value = 0;
102            n = 0;
103        }
104    
105        /**
106         * Returns the sum of the squares of the entries in the specified portion of
107         * the input array, or <code>Double.NaN</code> if the designated subarray
108         * is empty.
109         * <p>
110         * Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
111         *
112         * @param values the input array
113         * @param begin index of the first array element to include
114         * @param length the number of elements to include
115         * @return the sum of the squares of the values or 0 if length = 0
116         * @throws MathIllegalArgumentException if the array is null or the array index
117         *  parameters are not valid
118         */
119        @Override
120        public double evaluate(final double[] values,final int begin, final int length)
121        throws MathIllegalArgumentException {
122            double sumSq = Double.NaN;
123            if (test(values, begin, length, true)) {
124                sumSq = 0.0;
125                for (int i = begin; i < begin + length; i++) {
126                    sumSq += values[i] * values[i];
127                }
128            }
129            return sumSq;
130        }
131    
132        /**
133         * {@inheritDoc}
134         */
135        @Override
136        public SumOfSquares copy() {
137            SumOfSquares result = new SumOfSquares();
138            // no try-catch or advertised exception here because args are valid
139            copy(this, result);
140            return result;
141        }
142    
143        /**
144         * Copies source to dest.
145         * <p>Neither source nor dest can be null.</p>
146         *
147         * @param source SumOfSquares to copy
148         * @param dest SumOfSquares to copy to
149         * @throws NullArgumentException if either source or dest is null
150         */
151        public static void copy(SumOfSquares source, SumOfSquares dest)
152            throws NullArgumentException {
153            MathUtils.checkNotNull(source);
154            MathUtils.checkNotNull(dest);
155            dest.setData(source.getDataRef());
156            dest.n = source.n;
157            dest.value = source.value;
158        }
159    
160    }