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17 package org.apache.commons.math.stat.descriptive.moment;
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19 import junit.framework.Test;
20 import junit.framework.TestSuite;
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22 import org.apache.commons.math.stat.descriptive.StorelessUnivariateStatisticAbstractTest;
23 import org.apache.commons.math.stat.descriptive.UnivariateStatistic;
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30 public class VarianceTest extends StorelessUnivariateStatisticAbstractTest{
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32 protected Variance stat;
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37 public VarianceTest(String name) {
38 super(name);
39 }
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44 @Override
45 public UnivariateStatistic getUnivariateStatistic() {
46 return new Variance();
47 }
48
49 public static Test suite() {
50 TestSuite suite = new TestSuite(VarianceTest.class);
51 suite.setName("Variance Tests");
52 return suite;
53 }
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58 @Override
59 public double expectedValue() {
60 return this.var;
61 }
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66
67 public void testNaN() {
68 StandardDeviation std = new StandardDeviation();
69 assertTrue(Double.isNaN(std.getResult()));
70 std.increment(1d);
71 assertEquals(0d, std.getResult(), 0);
72 }
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77 public void testPopulation() {
78 double[] values = {-1.0d, 3.1d, 4.0d, -2.1d, 22d, 11.7d, 3d, 14d};
79 SecondMoment m = new SecondMoment();
80 m.evaluate(values);
81 Variance v1 = new Variance();
82 v1.setBiasCorrected(false);
83 assertEquals(populationVariance(values), v1.evaluate(values), 1E-14);
84 v1.incrementAll(values);
85 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
86 v1 = new Variance(false, m);
87 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
88 v1 = new Variance(false);
89 assertEquals(populationVariance(values), v1.evaluate(values), 1E-14);
90 v1.incrementAll(values);
91 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
92 }
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97 protected double populationVariance(double[] v) {
98 double mean = new Mean().evaluate(v);
99 double sum = 0;
100 for (int i = 0; i < v.length; i++) {
101 sum += (v[i] - mean) * (v[i] - mean);
102 }
103 return sum / v.length;
104 }
105
106 }