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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.MathArrays;
import org.hipparchus.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 AggregatableStatistic, Serializable {
/** Serializable version identifier */
private static final long serialVersionUID = 20150412L;
/** Number of values that have been added */
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 {
MathUtils.checkNotNull(original);
this.n = original.n;
this.value = original.value;
}
/** {@inheritDoc} */
@Override
public void increment(final double d) {
value += d * d;
n++;
}
/** {@inheritDoc} */
@Override
public double getResult() {
return value;
}
/** {@inheritDoc} */
@Override
public long getN() {
return n;
}
/** {@inheritDoc} */
@Override
public void clear() {
value = 0;
n = 0;
}
/** {@inheritDoc} */
@Override
public void aggregate(SumOfSquares other) {
MathUtils.checkNotNull(other);
if (other.n > 0) {
this.n += other.n;
this.value += other.value;
}
}
/**
* 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.
*
* @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 (MathArrays.verifyValues(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() {
return new SumOfSquares(this);
}
}