/*
 * 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.
/**
 * Returns the sum of the squares of the available values.
 * <p>
 * If there are no values in the dataset, then 0 is returned.
 * If any of the values are
 * <code>NaN</code>, then <code>NaN</code> is returned.</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 SumOfSquares extends AbstractStorelessUnivariateStatistic implements Serializable {

    
Serializable version identifier /** Serializable version identifier */
    private static final long serialVersionUID = 1460986908574398008L;

    /** */
    private long n;

    
The currently running sumSq
/**
     * The currently running sumSq
     */
    private double value;

    
Create a SumOfSquares instance
/**
     * Create a SumOfSquares instance
     */
    public SumOfSquares() {
        n = 0;
        value = 0;
    }

    
Copy constructor, creates a new SumOfSquares identical to the original 
Params:
original – the SumOfSquares instance to copy
Throws:
NullArgumentException – if original is null/**
     * 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}
/**
     * {@inheritDoc}
     */
    @Override
    public void increment(final double d) {
        value += d * d;
        n++;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public double getResult() {
        return value;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    public long getN() {
        return n;
    }

    
{@inheritDoc}
/**
     * {@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.
Params:
values – the input array
begin – index of the first array element to include
length – the number of elements to include
Throws:
MathIllegalArgumentException – if the array is null or the array index
 parameters are not valid
Returns:
the sum of the squares of the values or 0 if length = 0/**
     * Returns the sum of the squares 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>
     *
     * @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}
/**
     * {@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.
Params:
source – SumOfSquares to copy
dest – SumOfSquares to copy to
Throws:
NullArgumentException – if either source or dest is null/**
     * Copies source to dest.
     * <p>Neither source nor dest can be null.</p>
     *
     * @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;
    }

}