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/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.math3.stat.descriptive.moment; import java.io.Serializable; import org.apache.commons.math3.exception.MathIllegalArgumentException; import org.apache.commons.math3.exception.MathIllegalStateException; import org.apache.commons.math3.exception.NullArgumentException; import org.apache.commons.math3.exception.util.LocalizedFormats; import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic; import org.apache.commons.math3.stat.descriptive.StorelessUnivariateStatistic; import org.apache.commons.math3.stat.descriptive.summary.SumOfLogs; import org.apache.commons.math3.util.FastMath; import org.apache.commons.math3.util.MathUtils; /** * Returns the <a href="http://www.xycoon.com/geometric_mean.htm"> * geometric mean </a> of the available values. * <p> * Uses a {@link SumOfLogs} instance to compute sum of logs and returns * <code> exp( 1/n (sum of logs) ).</code> Therefore, </p> * <ul> * <li>If any of values are < 0, the result is <code>NaN.</code></li> * <li>If all values are non-negative and less than * <code>Double.POSITIVE_INFINITY</code>, but at least one value is 0, the * result is <code>0.</code></li> * <li>If both <code>Double.POSITIVE_INFINITY</code> and * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is * <code>NaN.</code></li> * </ul> </p> * <p> * <strong>Note that this implementation is not synchronized.</strong> If * multiple threads access an instance of this class concurrently, and at least * one of the threads invokes the <code>increment()</code> or * <code>clear()</code> method, it must be synchronized externally.</p> * * * @version $Id: GeometricMean.java 1416643 2012-12-03 19:37:14Z tn $ */ public class GeometricMean extends AbstractStorelessUnivariateStatistic implements Serializable { /** Serializable version identifier */ private static final long serialVersionUID = -8178734905303459453L; /** Wrapped SumOfLogs instance */ private StorelessUnivariateStatistic sumOfLogs; /** * Create a GeometricMean instance */ public GeometricMean() { sumOfLogs = new SumOfLogs(); } /** * Copy constructor, creates a new {@code GeometricMean} identical * to the {@code original} * * @param original the {@code GeometricMean} instance to copy * @throws NullArgumentException if original is null */ public GeometricMean(GeometricMean original) throws NullArgumentException { super(); copy(original, this); } /** * Create a GeometricMean instance using the given SumOfLogs instance * @param sumOfLogs sum of logs instance to use for computation */ public GeometricMean(SumOfLogs sumOfLogs) { this.sumOfLogs = sumOfLogs; } /** * {@inheritDoc} */ @Override public GeometricMean copy() { GeometricMean result = new GeometricMean(); // no try-catch or advertised exception because args guaranteed non-null copy(this, result); return result; } /** * {@inheritDoc} */ @Override public void increment(final double d) { sumOfLogs.increment(d); } /** * {@inheritDoc} */ @Override public double getResult() { if (sumOfLogs.getN() > 0) { return FastMath.exp(sumOfLogs.getResult() / sumOfLogs.getN()); } else { return Double.NaN; } } /** * {@inheritDoc} */ @Override public void clear() { sumOfLogs.clear(); } /** * Returns the geometric mean of the entries in the specified portion * of the input array. * <p> * See {@link GeometricMean} for details on the computing algorithm.</p> * <p> * Throws <code>IllegalArgumentException</code> if the array is null.</p> * * @param values input array containing the values * @param begin first array element to include * @param length the number of elements to include * @return the geometric mean or Double.NaN if length = 0 or * any of the values are <= 0. * @throws MathIllegalArgumentException if the input array is null or the array * index parameters are not valid */ @Override public double evaluate(final double[] values, final int begin, final int length) throws MathIllegalArgumentException { return FastMath.exp(sumOfLogs.evaluate(values, begin, length) / length); } /** * {@inheritDoc} */ public long getN() { return sumOfLogs.getN(); } /** * <p>Sets the implementation for the sum of logs.</p> * <p>This method must be activated before any data has been added - i.e., * before {@link #increment(double) increment} has been used to add data; * otherwise an IllegalStateException will be thrown.</p> * * @param sumLogImpl the StorelessUnivariateStatistic instance to use * for computing the log sum * @throws MathIllegalStateException if data has already been added * (i.e if n > 0) */ public void setSumLogImpl(StorelessUnivariateStatistic sumLogImpl) throws MathIllegalStateException { checkEmpty(); this.sumOfLogs = sumLogImpl; } /** * Returns the currently configured sum of logs implementation * * @return the StorelessUnivariateStatistic implementing the log sum */ public StorelessUnivariateStatistic getSumLogImpl() { return sumOfLogs; } /** * Copies source to dest. * <p>Neither source nor dest can be null.</p> * * @param source GeometricMean to copy * @param dest GeometricMean to copy to * @throws NullArgumentException if either source or dest is null */ public static void copy(GeometricMean source, GeometricMean dest) throws NullArgumentException { MathUtils.checkNotNull(source); MathUtils.checkNotNull(dest); dest.setData(source.getDataRef()); dest.sumOfLogs = source.sumOfLogs.copy(); } /** * Throws MathIllegalStateException if n > 0. * @throws MathIllegalStateException if data has been added to this statistic */ private void checkEmpty() throws MathIllegalStateException { if (getN() > 0) { throw new MathIllegalStateException(LocalizedFormats.VALUES_ADDED_BEFORE_CONFIGURING_STATISTIC, getN()); } } }