| /* |
| * 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.math.stat.descriptive.summary; |
| |
| import java.io.Serializable; |
| |
| import org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic; |
| import org.apache.commons.math.util.FastMath; |
| |
| /** |
| * Returns the sum of the natural logs for this collection of values. |
| * <p> |
| * Uses {@link java.lang.Math#log(double)} to compute the logs. Therefore, |
| * <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>Double.NEGATIVE_INFINITY.</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 $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $ |
| */ |
| public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements Serializable { |
| |
| /** Serializable version identifier */ |
| private static final long serialVersionUID = -370076995648386763L; |
| |
| /**Number of values that have been added */ |
| private int n; |
| |
| /** |
| * The currently running value |
| */ |
| private double value; |
| |
| /** |
| * Create a SumOfLogs instance |
| */ |
| public SumOfLogs() { |
| value = 0d; |
| n = 0; |
| } |
| |
| /** |
| * Copy constructor, creates a new {@code SumOfLogs} identical |
| * to the {@code original} |
| * |
| * @param original the {@code SumOfLogs} instance to copy |
| */ |
| public SumOfLogs(SumOfLogs original) { |
| copy(original, this); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public void increment(final double d) { |
| value += FastMath.log(d); |
| n++; |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public double getResult() { |
| if (n > 0) { |
| return value; |
| } else { |
| return Double.NaN; |
| } |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| public long getN() { |
| return n; |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public void clear() { |
| value = 0d; |
| n = 0; |
| } |
| |
| /** |
| * Returns the sum of the natural logs of the entries in the specified portion of |
| * the input array, or <code>Double.NaN</code> if the designated subarray |
| * is empty. |
| * <p> |
| * Throws <code>IllegalArgumentException</code> if the array is null.</p> |
| * <p> |
| * See {@link SumOfLogs}.</p> |
| * |
| * @param values the input array |
| * @param begin index of the first array element to include |
| * @param length the number of elements to include |
| * @return the sum of the natural logs of the values or Double.NaN if |
| * length = 0 |
| * @throws IllegalArgumentException if the array is null or the array index |
| * parameters are not valid |
| */ |
| @Override |
| public double evaluate(final double[] values, final int begin, final int length) { |
| double sumLog = Double.NaN; |
| if (test(values, begin, length)) { |
| sumLog = 0.0; |
| for (int i = begin; i < begin + length; i++) { |
| sumLog += FastMath.log(values[i]); |
| } |
| } |
| return sumLog; |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public SumOfLogs copy() { |
| SumOfLogs result = new SumOfLogs(); |
| copy(this, result); |
| return result; |
| } |
| |
| /** |
| * Copies source to dest. |
| * <p>Neither source nor dest can be null.</p> |
| * |
| * @param source SumOfLogs to copy |
| * @param dest SumOfLogs to copy to |
| * @throws NullPointerException if either source or dest is null |
| */ |
| public static void copy(SumOfLogs source, SumOfLogs dest) { |
| dest.setData(source.getDataRef()); |
| dest.n = source.n; |
| dest.value = source.value; |
| } |
| } |