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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 org.apache.commons.math.MathException;
20  
21  /**
22   * Base interface for probability distributions.
23   *
24   * @version $Revision: 670469 $ $Date: 2008-06-23 04:01:38 -0400 (Mon, 23 Jun 2008) $
25   */
26  public interface Distribution {
27      /**
28       * For a random variable X whose values are distributed according
29       * to this distribution, this method returns P(X ≤ x).  In other words,
30       * this method represents the  (cumulative) distribution function, or
31       * CDF, for this distribution.
32       * 
33       * @param x the value at which the distribution function is evaluated.
34       * @return the probability that a random variable with this
35       * distribution takes a value less than or equal to <code>x</code>
36       * @throws MathException if the cumulative probability can not be
37       * computed due to convergence or other numerical errors.
38       */
39      double cumulativeProbability(double x) throws MathException;
40      
41      /**
42       * For a random variable X whose values are distributed according
43       * to this distribution, this method returns P(x0 &le; X &le; x1).
44       * 
45       * @param x0 the (inclusive) lower bound
46       * @param x1 the (inclusive) upper bound
47       * @return the probability that a random variable with this distribution
48       * will take a value between <code>x0</code> and <code>x1</code>, 
49       * including the endpoints
50       * @throws MathException if the cumulative probability can not be
51       * computed due to convergence or other numerical errors.
52       * @throws IllegalArgumentException if <code>x0 > x1</code>
53       */
54      double cumulativeProbability(double x0, double x1) throws MathException;
55  }