    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.moment;
    018
    019    import java.io.Serializable;
    020
    021    import org.apache.commons.math3.exception.MathIllegalArgumentException;
    022    import org.apache.commons.math3.exception.MathIllegalStateException;
    023    import org.apache.commons.math3.exception.NullArgumentException;
    024    import org.apache.commons.math3.exception.util.LocalizedFormats;
    025    import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
    026    import org.apache.commons.math3.stat.descriptive.StorelessUnivariateStatistic;
    027    import org.apache.commons.math3.stat.descriptive.summary.SumOfLogs;
    028    import org.apache.commons.math3.util.FastMath;
    029    import org.apache.commons.math3.util.MathUtils;
    030
    031    /**
    032     * Returns the <a href="http://www.xycoon.com/geometric_mean.htm">
    033     * geometric mean </a> of the available values.
    034     * <p>
    035     * Uses a {@link SumOfLogs} instance to compute sum of logs and returns
    036     * <code> exp( 1/n  (sum of logs) ).</code>  Therefore, </p>
    037     * <ul>
    038     * <li>If any of values are < 0, the result is <code>NaN.</code></li>
    039     * <li>If all values are non-negative and less than
    040     * <code>Double.POSITIVE_INFINITY</code>,  but at least one value is 0, the
    041     * result is <code>0.</code></li>
    042     * <li>If both <code>Double.POSITIVE_INFINITY</code> and
    043     * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
    044     * <code>NaN.</code></li>
    045     * </ul> </p>
    046     * <p>
    047     * <strong>Note that this implementation is not synchronized.</strong> If
    048     * multiple threads access an instance of this class concurrently, and at least
    049     * one of the threads invokes the <code>increment()</code> or
    050     * <code>clear()</code> method, it must be synchronized externally.</p>
    051     *
    052     *
    053     * @version $Id: GeometricMean.java 1416643 2012-12-03 19:37:14Z tn $
    054     */
    055    public class GeometricMean extends AbstractStorelessUnivariateStatistic implements Serializable {
    056
    057        /** Serializable version identifier */
    058        private static final long serialVersionUID = -8178734905303459453L;
    059
    060        /** Wrapped SumOfLogs instance */
    061        private StorelessUnivariateStatistic sumOfLogs;
    062
    063        /**
    064         * Create a GeometricMean instance
    065         */
    066        public GeometricMean() {
    067            sumOfLogs = new SumOfLogs();
    068        }
    069
    070        /**
    071         * Copy constructor, creates a new {@code GeometricMean} identical
    072         * to the {@code original}
    073         *
    074         * @param original the {@code GeometricMean} instance to copy
    075         * @throws NullArgumentException if original is null
    076         */
    077        public GeometricMean(GeometricMean original) throws NullArgumentException {
    078            super();
    079            copy(original, this);
    080        }
    081
    082        /**
    083         * Create a GeometricMean instance using the given SumOfLogs instance
    084         * @param sumOfLogs sum of logs instance to use for computation
    085         */
    086        public GeometricMean(SumOfLogs sumOfLogs) {
    087            this.sumOfLogs = sumOfLogs;
    088        }
    089
    090        /**
    091         * {@inheritDoc}
    092         */
    093        @Override
    094        public GeometricMean copy() {
    095            GeometricMean result = new GeometricMean();
    096            // no try-catch or advertised exception because args guaranteed non-null
    097            copy(this, result);
    098            return result;
    099        }
    100
    101        /**
    102         * {@inheritDoc}
    103         */
    104        @Override
    105        public void increment(final double d) {
    106            sumOfLogs.increment(d);
    107        }
    108
    109        /**
    110         * {@inheritDoc}
    111         */
    112        @Override
    113        public double getResult() {
    114            if (sumOfLogs.getN() > 0) {
    115                return FastMath.exp(sumOfLogs.getResult() / sumOfLogs.getN());
    116            } else {
    117                return Double.NaN;
    118            }
    119        }
    120
    121        /**
    122         * {@inheritDoc}
    123         */
    124        @Override
    125        public void clear() {
    126            sumOfLogs.clear();
    127        }
    128
    129        /**
    130         * Returns the geometric mean of the entries in the specified portion
    131         * of the input array.
    132         * <p>
    133         * See {@link GeometricMean} for details on the computing algorithm.</p>
    134         * <p>
    135         * Throws <code>IllegalArgumentException</code> if the array is null.</p>
    136         *
    137         * @param values input array containing the values
    138         * @param begin first array element to include
    139         * @param length the number of elements to include
    140         * @return the geometric mean or Double.NaN if length = 0 or
    141         * any of the values are &lt;= 0.
    142         * @throws MathIllegalArgumentException if the input array is null or the array
    143         * index parameters are not valid
    144         */
    145        @Override
    146        public double evaluate(
    147            final double[] values, final int begin, final int length)
    148        throws MathIllegalArgumentException {
    149            return FastMath.exp(
    150                sumOfLogs.evaluate(values, begin, length) / length);
    151        }
    152
    153        /**
    154         * {@inheritDoc}
    155         */
    156        public long getN() {
    157            return sumOfLogs.getN();
    158        }
    159
    160        /**
    161         * <p>Sets the implementation for the sum of logs.</p>
    162         * <p>This method must be activated before any data has been added - i.e.,
    163         * before {@link #increment(double) increment} has been used to add data;
    164         * otherwise an IllegalStateException will be thrown.</p>
    165         *
    166         * @param sumLogImpl the StorelessUnivariateStatistic instance to use
    167         * for computing the log sum
    168         * @throws MathIllegalStateException if data has already been added
    169         *  (i.e if n > 0)
    170         */
    171        public void setSumLogImpl(StorelessUnivariateStatistic sumLogImpl)
    172        throws MathIllegalStateException {
    173            checkEmpty();
    174            this.sumOfLogs = sumLogImpl;
    175        }
    176
    177        /**
    178         * Returns the currently configured sum of logs implementation
    179         *
    180         * @return the StorelessUnivariateStatistic implementing the log sum
    181         */
    182        public StorelessUnivariateStatistic getSumLogImpl() {
    183            return sumOfLogs;
    184        }
    185
    186        /**
    187         * Copies source to dest.
    188         * <p>Neither source nor dest can be null.</p>
    189         *
    190         * @param source GeometricMean to copy
    191         * @param dest GeometricMean to copy to
    192         * @throws NullArgumentException if either source or dest is null
    193         */
    194        public static void copy(GeometricMean source, GeometricMean dest)
    195            throws NullArgumentException {
    196            MathUtils.checkNotNull(source);
    197            MathUtils.checkNotNull(dest);
    198            dest.setData(source.getDataRef());
    199            dest.sumOfLogs = source.sumOfLogs.copy();
    200        }
    201
    202
    203        /**
    204         * Throws MathIllegalStateException if n > 0.
    205         * @throws MathIllegalStateException if data has been added to this statistic
    206         */
    207        private void checkEmpty() throws MathIllegalStateException {
    208            if (getN() > 0) {
    209                throw new MathIllegalStateException(
    210                        LocalizedFormats.VALUES_ADDED_BEFORE_CONFIGURING_STATISTIC,
    211                        getN());
    212            }
    213        }
    214
    215    }