Coverage Report - org.apache.commons.math.distribution.BinomialDistributionImpl

Classes in this File	Line Coverage	Branch Coverage	Complexity
BinomialDistributionImpl	100%	100%	2.1;2.1

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.distribution;
17
18		import java.io.Serializable;
19
20		import org.apache.commons.math.MathException;
21		import org.apache.commons.math.special.Beta;
22		import org.apache.commons.math.util.MathUtils;
23
24		/**
25		* The default implementation of {@link BinomialDistribution}.
26		*
27		* @version $Revision$ $Date: 2005-06-26 15:20:57 -0700 (Sun, 26 Jun 2005) $
28		*/
29		public class BinomialDistributionImpl
30		extends AbstractIntegerDistribution
31		implements BinomialDistribution, Serializable {
32
33		/** Serializable version identifier */
34		static final long serialVersionUID = 6751309484392813623L;
35
36		/** The number of trials. */
37		private int numberOfTrials;
38
39		/** The probability of success. */
40		private double probabilityOfSuccess;
41
42		/**
43		* Create a binomial distribution with the given number of trials and
44		* probability of success.
45		* @param trials the number of trials.
46		* @param p the probability of success.
47		*/
48		public BinomialDistributionImpl(int trials, double p) {
49	30	super();
50	30	setNumberOfTrials(trials);
51	28	setProbabilityOfSuccess(p);
52	24	}
53
54		/**
55		* Access the number of trials for this distribution.
56		* @return the number of trials.
57		*/
58		public int getNumberOfTrials() {
59	540	return numberOfTrials;
60		}
61
62		/**
63		* Access the probability of success for this distribution.
64		* @return the probability of success.
65		*/
66		public double getProbabilityOfSuccess() {
67	258	return probabilityOfSuccess;
68		}
69
70		/**
71		* Change the number of trials for this distribution.
72		* @param trials the new number of trials.
73		* @throws IllegalArgumentException if <code>trials</code> is not a valid
74		* number of trials.
75		*/
76		public void setNumberOfTrials(int trials) {
77	30	if (trials < 0) {
78	2	throw new IllegalArgumentException("number of trials must be non-negative.");
79		}
80	28	numberOfTrials = trials;
81	28	}
82
83		/**
84		* Change the probability of success for this distribution.
85		* @param p the new probability of success.
86		* @throws IllegalArgumentException if <code>p</code> is not a valid
87		* probability.
88		*/
89		public void setProbabilityOfSuccess(double p) {
90	28	if (p < 0.0 || p > 1.0) {
91	4	throw new IllegalArgumentException("probability of success must be between 0.0 and 1.0, inclusive.");
92		}
93	24	probabilityOfSuccess = p;
94	24	}
95
96		/**
97		* Access the domain value lower bound, based on <code>p</code>, used to
98		* bracket a PDF root.
99		*
100		* @param p the desired probability for the critical value
101		* @return domain value lower bound, i.e.
102		* P(X &lt; <i>lower bound</i>) &lt; <code>p</code>
103		*/
104		protected int getDomainLowerBound(double p) {
105	28	return -1;
106		}
107
108		/**
109		* Access the domain value upper bound, based on <code>p</code>, used to
110		* bracket a PDF root.
111		*
112		* @param p the desired probability for the critical value
113		* @return domain value upper bound, i.e.
114		* P(X &lt; <i>upper bound</i>) &gt; <code>p</code>
115		*/
116		protected int getDomainUpperBound(double p) {
117	28	return getNumberOfTrials();
118		}
119
120		/**
121		* For this distribution, X, this method returns P(X &le; x).
122		* @param x the value at which the PDF is evaluated.
123		* @return PDF for this distribution.
124		* @throws MathException if the cumulative probability can not be
125		* computed due to convergence or other numerical errors.
126		*/
127		public double cumulativeProbability(int x) throws MathException {
128		double ret;
129	226	if (x < 0) {
130	14	ret = 0.0;
131	212	} else if (x >= getNumberOfTrials()) {
132	22	ret = 1.0;
133		} else {
134	190	ret =
135		1.0 - Beta.regularizedBeta(
136		getProbabilityOfSuccess(),
137		x + 1.0,
138		getNumberOfTrials() - x);
139		}
140	226	return ret;
141		}
142
143		/**
144		* For this disbution, X, this method returns P(X = x).
145		*
146		* @param x the value at which the PMF is evaluated.
147		* @return PMF for this distribution.
148		*/
149		public double probability(int x) {
150		double ret;
151	48	if (x < 0 || x > getNumberOfTrials()) {
152	14	ret = 0.0;
153		} else {
154	34	ret = MathUtils.binomialCoefficientDouble(
155		getNumberOfTrials(), x) *
156		Math.pow(getProbabilityOfSuccess(), x) *
157		Math.pow(1.0 - getProbabilityOfSuccess(),
158		getNumberOfTrials() - x);
159		}
160	48	return ret;
161		}
162
163		/**
164		* For this distribution, X, this method returns the largest x, such
165		* that P(X &le; x) &le; <code>p</code>.
166		* <p>
167		* Returns <code>-1</code> for p=0 and <code>Integer.MAX_VALUE</code> for
168		* p=1.
169		*
170		* @param p the desired probability
171		* @return the largest x such that P(X &le; x) <= p
172		* @throws MathException if the inverse cumulative probability can not be
173		* computed due to convergence or other numerical errors.
174		* @throws IllegalArgumentException if p < 0 or p > 1
175		*/
176		public int inverseCumulativeProbability(final double p) throws MathException {
177		// handle extreme values explicitly
178	36	if (p == 0) {
179	2	return -1;
180		}
181	34	if (p == 1) {
182	2	return Integer.MAX_VALUE;
183		}
184
185		// use default bisection impl
186	32	return super.inverseCumulativeProbability(p);
187		}
188		}