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1   /*
2    * Copyright 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  
22  /**
23   * Base class for probability distributions.   
24   *  
25   * @version $Revision: 348519 $ $Date: 2005-11-23 12:12:18 -0700 (Wed, 23 Nov 2005) $
26   */
27  public abstract class AbstractDistribution
28      implements Distribution, Serializable {
29  
30      /** Serializable version identifier */
31      private static final long serialVersionUID = -38038050983108802L;
32      
33      /**
34       * Default constructor.
35       */
36      protected AbstractDistribution() {
37          super();
38      }
39  
40      /**
41       * For a random variable X whose values are distributed according
42       * to this distribution, this method returns P(x0 ≤ X ≤ x1).
43       * <p>
44       * The default implementation uses the identity
45       * <p>
46       * P(x0 &le; X &le; x1) = P(X &le; x1) - P(X &le; x0)
47       * 
48       * @param x0 the (inclusive) lower bound
49       * @param x1 the (inclusive) upper bound
50       * @return the probability that a random variable with this distribution
51       * will take a value between <code>x0</code> and <code>x1</code>,
52       * including the endpoints.
53       * @throws MathException if the cumulative probability can not be
54       * computed due to convergence or other numerical errors.
55       * @throws IllegalArgumentException if <code>x0 > x1</code>
56       */
57      public double cumulativeProbability(double x0, double x1)
58          throws MathException {
59          if (x0 > x1) {
60              throw new IllegalArgumentException
61              ("lower endpoint must be less than or equal to upper endpoint");
62          }
63          return cumulativeProbability(x1) - cumulativeProbability(x0);
64      }
65  }