1   /*
2    * Copyright 2003-2004 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  /**
19   * Test cases for ExponentialDistribution.
20   * Extends ContinuousDistributionAbstractTest.  See class javadoc for
21   * ContinuousDistributionAbstractTest for details.
22   * 
23   * @version $Revision: 155427 $ $Date: 2005-02-26 06:11:52 -0700 (Sat, 26 Feb 2005) $
24   */
25  public class ExponentialDistributionTest extends ContinuousDistributionAbstractTest {
26  
27      /**
28       * Constructor for ExponentialDistributionTest.
29       * @param name
30       */
31      public ExponentialDistributionTest(String name) {
32          super(name);
33      }
34  
35      //-------------- Implementations for abstract methods -----------------------
36      
37      /** Creates the default continuous distribution instance to use in tests. */
38      public ContinuousDistribution makeDistribution() {
39          return DistributionFactory.newInstance().createExponentialDistribution(5.0);
40      }   
41      
42      /** Creates the default cumulative probability distribution test input values */
43      public double[] makeCumulativeTestPoints() {
44          // quantiles computed using R version 1.8.1 (linux version)
45          return new double[] {0.005002502d, 0.05025168d, 0.1265890d, 0.2564665d, 0.5268026d, 
46                  34.53878d, 23.02585d, 18.44440d, 14.97866d, 11.51293d};
47      }
48      
49      /** Creates the default cumulative probability density test expected values */
50      public double[] makeCumulativeTestValues() {
51          return new double[] {0.001d, 0.01d, 0.025d, 0.05d, 0.1d, 0.999d,
52                  0.990d, 0.975d, 0.950d, 0.900d}; 
53      }
54      
55      //------------ Additional tests -------------------------------------------
56   
57      public void testCumulativeProbabilityExtremes() throws Exception {
58          setCumulativeTestPoints(new double[] {-2, 0});
59          setCumulativeTestValues(new double[] {0, 0});
60          verifyCumulativeProbabilities();
61      }
62  
63      public void testInverseCumulativeProbabilityExtremes() throws Exception {
64           setInverseCumulativeTestPoints(new double[] {0, 1});
65           setInverseCumulativeTestValues(new double[] {0, Double.POSITIVE_INFINITY});
66           verifyInverseCumulativeProbabilities();
67      }
68  
69      public void testCumulativeProbability2() throws Exception {
70          double actual = getDistribution().cumulativeProbability(0.25, 0.75);
71          assertEquals(0.0905214, actual, 10e-4);
72      }
73      
74      public void testMeanAccessors() {
75          ExponentialDistribution distribution = (ExponentialDistribution) getDistribution();
76          assertEquals(5d, distribution.getMean(), Double.MIN_VALUE);
77          distribution.setMean(2d);
78          assertEquals(2d, distribution.getMean(), Double.MIN_VALUE);
79          try {
80              distribution.setMean(0);
81              fail("Expecting IllegalArgumentException for 0 mean");
82          } catch (IllegalArgumentException ex) {
83              // expected
84          }
85      }
86     
87  }