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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.
*/
/*
* This is not the original file distributed by the Apache Software Foundation
* It has been modified by the Hipparchus project
*/
package org.hipparchus.stat.descriptive.summary;
import java.io.Serializable;
import org.hipparchus.exception.MathIllegalArgumentException;
import org.hipparchus.exception.NullArgumentException;
import org.hipparchus.stat.descriptive.AbstractStorelessUnivariateStatistic;
import org.hipparchus.stat.descriptive.AggregatableStatistic;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathArrays;
import org.hipparchus.util.MathUtils;
/**
* Returns the sum of the natural logs for this collection of values.
*
* Uses {@link org.hipparchus.util.FastMath#log(double)} to compute the logs.
* Therefore,
*
* - If any of values are < 0, the result is
NaN.
* - If all values are non-negative and less than
*
Double.POSITIVE_INFINITY, but at least one value is 0, the
* result is Double.NEGATIVE_INFINITY.
* - If both
Double.POSITIVE_INFINITY and
* Double.NEGATIVE_INFINITY are among the values, the result is
* NaN.
*
*
* 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 increment() or
* clear() method, it must be synchronized externally.
*/
public class SumOfLogs extends AbstractStorelessUnivariateStatistic
implements AggregatableStatistic, Serializable {
/** Serializable version identifier */
private static final long serialVersionUID = 20150412L;
/** 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 {
MathUtils.checkNotNull(original);
this.n = original.n;
this.value = original.value;
}
/** {@inheritDoc} */
@Override
public void increment(final double d) {
value += FastMath.log(d);
n++;
}
/** {@inheritDoc} */
@Override
public double getResult() {
return value;
}
/** {@inheritDoc} */
@Override
public long getN() {
return n;
}
/** {@inheritDoc} */
@Override
public void clear() {
value = 0d;
n = 0;
}
/** {@inheritDoc} */
@Override
public void aggregate(SumOfLogs other) {
MathUtils.checkNotNull(other);
if (other.n > 0) {
this.n += other.n;
this.value += other.value;
}
}
/**
* Returns the sum of the natural logs of the entries in the specified portion of
* the input array, or Double.NaN if the designated subarray
* is empty.
*
* @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 (MathArrays.verifyValues(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() {
return new SumOfLogs(this);
}
}