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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  
23  /**
24   * Base class for probability distributions.   
25   *  
26   * @version $Revision: 617953 $ $Date: 2008-02-02 22:54:00 -0700 (Sat, 02 Feb 2008) $
27   */
28  public abstract class AbstractDistribution
29      implements Distribution, Serializable {
30  
31      /** Serializable version identifier */
32      private static final long serialVersionUID = -38038050983108802L;
33      
34      /**
35       * Default constructor.
36       */
37      protected AbstractDistribution() {
38          super();
39      }
40  
41      /**
42       * For a random variable X whose values are distributed according
43       * to this distribution, this method returns P(x0 ≤ X ≤ x1).
44       * <p>
45       * The default implementation uses the identity</p>
46       * <p>
47       * P(x0 &le; X &le; x1) = P(X &le; x1) - P(X &le; x0) </p>
48       * 
49       * @param x0 the (inclusive) lower bound
50       * @param x1 the (inclusive) upper bound
51       * @return the probability that a random variable with this distribution
52       * will take a value between <code>x0</code> and <code>x1</code>,
53       * including the endpoints.
54       * @throws MathException if the cumulative probability can not be
55       * computed due to convergence or other numerical errors.
56       * @throws IllegalArgumentException if <code>x0 > x1</code>
57       */
58      public double cumulativeProbability(double x0, double x1)
59          throws MathException {
60          if (x0 > x1) {
61              throw new IllegalArgumentException
62              ("lower endpoint must be less than or equal to upper endpoint");
63          }
64          return cumulativeProbability(x1) - cumulativeProbability(x0);
65      }
66  }