Coverage Report - org.apache.commons.math.stat.descriptive.moment.ThirdMoment

Classes in this File	Line Coverage	Branch Coverage	Complexity
ThirdMoment	100%	100%	1.25;1.25

1		/*
2		* Copyright 2003-2004 The Apache Software Foundation.
3		*
4		* Licensed under the Apache License, Version 2.0 (the "License");
5		* you may not use this file except in compliance with the License.
6		* You may obtain a copy of the License at
7		*
8		* http://www.apache.org/licenses/LICENSE-2.0
9		*
10		* Unless required by applicable law or agreed to in writing, software
11		* distributed under the License is distributed on an "AS IS" BASIS,
12		* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13		* See the License for the specific language governing permissions and
14		* limitations under the License.
15		*/
16		package org.apache.commons.math.stat.descriptive.moment;
17
18		import java.io.Serializable;
19
20		/**
21		* Computes a statistic related to the Third Central Moment. Specifically,
22		* what is computed is the sum of cubed deviations from the sample mean.
23		* <p>
24		* The following recursive updating formula is used:
25		* <p>
26		* Let <ul>
27		* <li> dev = (current obs - previous mean) </li>
28		* <li> m2 = previous value of {@link SecondMoment} </li>
29		* <li> n = number of observations (including current obs) </li>
30		* </ul>
31		* Then
32		* <p>
33		* new value = old value - 3 * (dev/n) * m2 + (n-1) * (n -2) * (dev^3/n^2)
34		* <p>
35		* Returns <code>Double.NaN</code> if no data values have been added and
36		* returns <code>0</code> if there is just one value in the data set.
37		* <p>
38		* <strong>Note that this implementation is not synchronized.</strong> If
39		* multiple threads access an instance of this class concurrently, and at least
40		* one of the threads invokes the <code>increment()</code> or
41		* <code>clear()</code> method, it must be synchronized externally.
42		*
43		* @version $Revision$ $Date: 2005-02-26 05:11:52 -0800 (Sat, 26 Feb 2005) $
44		*/
45		public class ThirdMoment extends SecondMoment implements Serializable {
46
47		/** Serializable version identifier */
48		static final long serialVersionUID = -7818711964045118679L;
49
50		/** third moment of values that have been added */
51		protected double m3;
52
53		/**
54		* Square of deviation of most recently added value from previous first
55		* moment, normalized by previous sample size. Retained to prevent
56		* repeated computation in higher order moments. nDevSq = nDev * nDev.
57		*/
58		protected double nDevSq;
59
60		/**
61		* Create a FourthMoment instance
62		*/
63		public ThirdMoment() {
64	98	super();
65	98	m3 = Double.NaN;
66	98	nDevSq = Double.NaN;
67	98	}
68
69		/**
70		* @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#increment(double)
71		*/
72		public void increment(final double d) {
73	918	if (n < 1) {
74	106	m3 = m2 = m1 = 0.0;
75		}
76
77	918	double prevM2 = m2;
78	918	super.increment(d);
79	918	nDevSq = nDev * nDev;
80	918	double n0 = (double) n;
81	918	m3 = m3 - 3.0 * nDev * prevM2 + (n0 - 1) * (n0 - 2) * nDevSq * dev;
82	918	}
83
84		/**
85		* @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#getResult()
86		*/
87		public double getResult() {
88	104	return m3;
89		}
90
91		/**
92		* @see org.apache.commons.math.stat.descriptive.StorelessUnivariateStatistic#clear()
93		*/
94		public void clear() {
95	112	super.clear();
96	112	m3 = Double.NaN;
97	112	nDevSq = Double.NaN;
98	112	}
99
100		}