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Commons Math example source code file (SumOfLogs.java)
This example Commons Math source code file (SumOfLogs.java) is included in the DevDaily.com
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The Commons Math SumOfLogs.java source code
/*
* 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;
/**
* 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 NaN.
* <li>If all values are non-negative and less than
* <code>Double.POSITIVE_INFINITY, but at least one value is 0, the
* result is <code>Double.NEGATIVE_INFINITY.
* <li>If both Double.POSITIVE_INFINITY and
* <code>Double.NEGATIVE_INFINITY are among the values, the result is
* <code>NaN.
* </ul>
* <p>
* <strong>Note that this implementation is not synchronized. If
* multiple threads access an instance of this class concurrently, and at least
* one of the threads invokes the <code>increment() or
* <code>clear() method, it must be synchronized externally.
*
* @version $Revision: 811685 $ $Date: 2009-09-05 13:36:48 -0400 (Sat, 05 Sep 2009) $
*/
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 += Math.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 if the designated subarray
* is empty.
* <p>
* Throws <code>IllegalArgumentException if the array is null.
* <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 += Math.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.
*
* @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.n = source.n;
dest.value = source.value;
}
}
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