1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 /*
19 * This is not the original file distributed by the Apache Software Foundation
20 * It has been modified by the Hipparchus project
21 */
22
23 package org.hipparchus.distribution.continuous;
24
25 import org.hipparchus.exception.LocalizedCoreFormats;
26 import org.hipparchus.exception.MathIllegalArgumentException;
27 import org.hipparchus.util.MathUtils;
28
29 /**
30 * Implementation of the uniform real distribution.
31 *
32 * @see <a href="http://en.wikipedia.org/wiki/Uniform_distribution_(continuous)">
33 * Uniform distribution (continuous), at Wikipedia</a>
34 */
35 public class UniformRealDistribution extends AbstractRealDistribution {
36 /** Serializable version identifier. */
37 private static final long serialVersionUID = 20120109L;
38 /** Lower bound of this distribution (inclusive). */
39 private final double lower;
40 /** Upper bound of this distribution (exclusive). */
41 private final double upper;
42
43 /**
44 * Create a standard uniform real distribution with lower bound (inclusive)
45 * equal to zero and upper bound (exclusive) equal to one.
46 */
47 public UniformRealDistribution() {
48 this(0, 1);
49 }
50
51 /**
52 * Create a uniform real distribution using the given lower and upper
53 * bounds.
54 *
55 * @param lower Lower bound of this distribution (inclusive).
56 * @param upper Upper bound of this distribution (exclusive).
57 * @throws MathIllegalArgumentException if {@code lower >= upper}.
58 */
59 public UniformRealDistribution(double lower, double upper)
60 throws MathIllegalArgumentException {
61 super();
62 if (lower >= upper) {
63 throw new MathIllegalArgumentException(
64 LocalizedCoreFormats.LOWER_BOUND_NOT_BELOW_UPPER_BOUND,
65 lower, upper, false);
66 }
67
68 this.lower = lower;
69 this.upper = upper;
70 }
71
72 /** {@inheritDoc} */
73 @Override
74 public double density(double x) {
75 if (x < lower || x > upper) {
76 return 0.0;
77 }
78 return 1 / (upper - lower);
79 }
80
81 /** {@inheritDoc} */
82 @Override
83 public double cumulativeProbability(double x) {
84 if (x <= lower) {
85 return 0;
86 }
87 if (x >= upper) {
88 return 1;
89 }
90 return (x - lower) / (upper - lower);
91 }
92
93 /** {@inheritDoc} */
94 @Override
95 public double inverseCumulativeProbability(final double p)
96 throws MathIllegalArgumentException {
97 MathUtils.checkRangeInclusive(p, 0, 1);
98 return p * (upper - lower) + lower;
99 }
100
101 /**
102 * {@inheritDoc}
103 *
104 * For lower bound {@code lower} and upper bound {@code upper}, the mean is
105 * {@code 0.5 * (lower + upper)}.
106 */
107 @Override
108 public double getNumericalMean() {
109 return 0.5 * (lower + upper);
110 }
111
112 /**
113 * {@inheritDoc}
114 *
115 * For lower bound {@code lower} and upper bound {@code upper}, the
116 * variance is {@code (upper - lower)^2 / 12}.
117 */
118 @Override
119 public double getNumericalVariance() {
120 double ul = upper - lower;
121 return ul * ul / 12;
122 }
123
124 /**
125 * {@inheritDoc}
126 *
127 * The lower bound of the support is equal to the lower bound parameter
128 * of the distribution.
129 *
130 * @return lower bound of the support
131 */
132 @Override
133 public double getSupportLowerBound() {
134 return lower;
135 }
136
137 /**
138 * {@inheritDoc}
139 *
140 * The upper bound of the support is equal to the upper bound parameter
141 * of the distribution.
142 *
143 * @return upper bound of the support
144 */
145 @Override
146 public double getSupportUpperBound() {
147 return upper;
148 }
149
150 /**
151 * {@inheritDoc}
152 *
153 * The support of this distribution is connected.
154 *
155 * @return {@code true}
156 */
157 @Override
158 public boolean isSupportConnected() {
159 return true;
160 }
161
162 }