/*
 * 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.FastMath;
import org.apache.commons.math3.util.MathUtils;

Returns the sum of the natural logs for this collection of values.
 Uses 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.
/**
 * Returns the sum of the natural logs for this collection of values.
 * <p>
 * Uses {@link org.apache.commons.math3.util.FastMath#log(double)} to compute the logs.
 * Therefore,
 * <ul>
 * <li>If any of values are &lt; 0, the result is <code>NaN.</code></li>
 * <li>If all values are non-negative and less than
 * <code>Double.POSITIVE_INFINITY</code>,  but at least one value is 0, the
 * result is <code>Double.NEGATIVE_INFINITY.</code></li>
 * <li>If both <code>Double.POSITIVE_INFINITY</code> and
 * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
 * <code>NaN.</code></li>
 * </ul></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 SumOfLogs extends AbstractStorelessUnivariateStatistic implements Serializable {

    
Serializable version identifier /** Serializable version identifier */
    private static final long serialVersionUID = -370076995648386763L;

    
Number of values that have been added /**Number of values that have been added */
    private int n;

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

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

    
Copy constructor, creates a new SumOfLogs identical to the original 
Params:
original – the SumOfLogs instance to copy
Throws:
NullArgumentException – if original is null/**
     * 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 {
        copy(original, this);
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void increment(final double d) {
        value += FastMath.log(d);
        n++;
    }

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

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

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void clear() {
        value = 0d;
        n = 0;
    }

    
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.

Throws MathIllegalArgumentException if the array is null.
 See SumOfLogs.
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 natural logs of the values or 0 if
length = 0/**
     * Returns the sum of the natural logs 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>
     * <p>
     * See {@link SumOfLogs}.</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 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 (test(values, begin, length, true)) {
            sumLog = 0.0;
            for (int i = begin; i < begin + length; i++) {
                sumLog += FastMath.log(values[i]);
            }
        }
        return sumLog;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public SumOfLogs copy() {
        SumOfLogs result = new SumOfLogs();
        // 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 – SumOfLogs to copy
dest – SumOfLogs 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 SumOfLogs to copy
     * @param dest SumOfLogs to copy to
     * @throws NullArgumentException if either source or dest is null
     */
    public static void copy(SumOfLogs source, SumOfLogs dest)
        throws NullArgumentException {
        MathUtils.checkNotNull(source);
        MathUtils.checkNotNull(dest);
        dest.setData(source.getDataRef());
        dest.n = source.n;
        dest.value = source.value;
    }
}