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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 public UnivariateStatistic getUnivariateStatistic() {
45 return new Variance();
46 }
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48 public static Test suite() {
49 TestSuite suite = new TestSuite(VarianceTest.class);
50 suite.setName("Variance Tests");
51 return suite;
52 }
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57 public double expectedValue() {
58 return this.var;
59 }
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65 public void testNaN() {
66 StandardDeviation std = new StandardDeviation();
67 assertTrue(Double.isNaN(std.getResult()));
68 std.increment(1d);
69 assertEquals(0d, std.getResult(), 0);
70 }
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75 public void testPopulation() {
76 double[] values = {-1.0d, 3.1d, 4.0d, -2.1d, 22d, 11.7d, 3d, 14d};
77 SecondMoment m = new SecondMoment();
78 m.evaluate(values);
79 Variance v1 = new Variance();
80 v1.setBiasCorrected(false);
81 assertEquals(populationVariance(values), v1.evaluate(values), 1E-14);
82 v1.incrementAll(values);
83 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
84 v1 = new Variance(false, m);
85 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
86 v1 = new Variance(false);
87 assertEquals(populationVariance(values), v1.evaluate(values), 1E-14);
88 v1.incrementAll(values);
89 assertEquals(populationVariance(values), v1.getResult(), 1E-14);
90 }
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95 protected double populationVariance(double[] v) {
96 double mean = new Mean().evaluate(v);
97 double sum = 0;
98 for (int i = 0; i < v.length; i++) {
99 sum += (v[i] - mean) * (v[i] - mean);
100 }
101 return sum / (double) v.length;
102 }
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104 }