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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.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; } }




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