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The Apache Commons Math project is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language or commons-lang.
/*
* 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.MathUtils;
/**
* Returns the sum of the squares of the available values.
*
* If there are no values in the dataset, then 0 is returned.
* If any of the values are
* NaN, then NaN is returned.
*
* 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 SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable {
/** Serializable version identifier */
private static final long serialVersionUID = 1460986908574398008L;
/** */
private long n;
/**
* The currently running sumSq
*/
private double value;
/**
* Create a SumOfSquares instance
*/
public SumOfSquares() {
n = 0;
value = 0;
}
/**
* Copy constructor, creates a new {@code SumOfSquares} identical
* to the {@code original}
*
* @param original the {@code SumOfSquares} instance to copy
* @throws NullArgumentException if original is null
*/
public SumOfSquares(SumOfSquares original) throws NullArgumentException {
copy(original, this);
}
/**
* {@inheritDoc}
*/
@Override
public void increment(final double d) {
value += d * d;
n++;
}
/**
* {@inheritDoc}
*/
@Override
public double getResult() {
return value;
}
/**
* {@inheritDoc}
*/
public long getN() {
return n;
}
/**
* {@inheritDoc}
*/
@Override
public void clear() {
value = 0;
n = 0;
}
/**
* Returns the sum of the squares of the entries in the specified portion of
* the input array, or Double.NaN if the designated subarray
* is empty.
*
* Throws MathIllegalArgumentException if the array is null.
*
* @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 squares 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 sumSq = Double.NaN;
if (test(values, begin, length, true)) {
sumSq = 0.0;
for (int i = begin; i < begin + length; i++) {
sumSq += values[i] * values[i];
}
}
return sumSq;
}
/**
* {@inheritDoc}
*/
@Override
public SumOfSquares copy() {
SumOfSquares result = new SumOfSquares();
// no try-catch or advertised exception here because args are valid
copy(this, result);
return result;
}
/**
* Copies source to dest.
* Neither source nor dest can be null.
*
* @param source SumOfSquares to copy
* @param dest SumOfSquares to copy to
* @throws NullArgumentException if either source or dest is null
*/
public static void copy(SumOfSquares source, SumOfSquares dest)
throws NullArgumentException {
MathUtils.checkNotNull(source);
MathUtils.checkNotNull(dest);
dest.setData(source.getDataRef());
dest.n = source.n;
dest.value = source.value;
}
}