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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    *      http://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  package org.apache.commons.math.distribution;
18  
19  import java.io.Serializable;
20  
21  import org.apache.commons.math.MathException;
22  import org.apache.commons.math.MathRuntimeException;
23  
24  /**
25   * Base class for probability distributions.   
26   *  
27   * @version $Revision: 772119 $ $Date: 2009-05-06 05:43:28 -0400 (Wed, 06 May 2009) $
28   */
29  public abstract class AbstractDistribution
30      implements Distribution, Serializable {
31  
32      /** Serializable version identifier */
33      private static final long serialVersionUID = -38038050983108802L;
34      
35      /**
36       * Default constructor.
37       */
38      protected AbstractDistribution() {
39          super();
40      }
41  
42      /**
43       * For a random variable X whose values are distributed according
44       * to this distribution, this method returns P(x0 ≤ X ≤ x1).
45       * <p>
46       * The default implementation uses the identity</p>
47       * <p>
48       * P(x0 &le; X &le; x1) = P(X &le; x1) - P(X &le; x0) </p>
49       * 
50       * @param x0 the (inclusive) lower bound
51       * @param x1 the (inclusive) upper bound
52       * @return the probability that a random variable with this distribution
53       * will take a value between <code>x0</code> and <code>x1</code>,
54       * including the endpoints.
55       * @throws MathException if the cumulative probability can not be
56       * computed due to convergence or other numerical errors.
57       * @throws IllegalArgumentException if <code>x0 > x1</code>
58       */
59      public double cumulativeProbability(double x0, double x1)
60          throws MathException {
61          if (x0 > x1) {
62              throw MathRuntimeException.createIllegalArgumentException(
63                    "lower endpoint ({0}) must be less than or equal to upper endpoint ({1})",
64                    x0, x1);
65          }
66          return cumulativeProbability(x1) - cumulativeProbability(x0);
67      }
68  }