    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: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $
    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.setData(source.getDataRef());
    150            dest.n = source.n;
    151            dest.value = source.value;
    152        }
    153
    154    }