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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.summary;
import java.io.Serializable;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathUtils;
/**
* Returns the sum of the natural logs for this collection of values.
* <p>
* Uses {@link org.apache.commons.math3.util.FastMath#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>
*
*/
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
* @throws NullArgumentException if original is null
*/
public SumOfLogs(SumOfLogs original) throws NullArgumentException {
copy(original, this);
}
/**
* {@inheritDoc}
*/
@Override
public void increment(final double d) {
value += FastMath.log(d);
n++;
}
/**
* {@inheritDoc}
*/
@Override
public double getResult() {
return value;
}
/**
* {@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>MathIllegalArgumentException</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 0 if
* length = 0
* @throws MathIllegalArgumentException 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)
throws MathIllegalArgumentException {
double sumLog = Double.NaN;
if (test(values, begin, length, true)) {
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();
// No try-catch or advertised exception here because args are valid
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 NullArgumentException if either source or dest is null
*/
public static void copy(SumOfLogs source, SumOfLogs dest)
throws NullArgumentException {
MathUtils.checkNotNull(source);
MathUtils.checkNotNull(dest);
dest.setData(source.getDataRef());
dest.n = source.n;
dest.value = source.value;
}
}
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