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16 package org.apache.commons.math.stat.descriptive.moment;
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18 import junit.framework.Test;
19 import junit.framework.TestSuite;
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21 import org.apache.commons.math.stat.descriptive.StorelessUnivariateStatisticAbstractTest;
22 import org.apache.commons.math.stat.descriptive.UnivariateStatistic;
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29 public class StandardDeviationTest extends StorelessUnivariateStatisticAbstractTest{
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31 protected StandardDeviation stat;
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36 public StandardDeviationTest(String name) {
37 super(name);
38 }
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43 public UnivariateStatistic getUnivariateStatistic() {
44 return new StandardDeviation();
45 }
46
47 public static Test suite() {
48 TestSuite suite = new TestSuite(StandardDeviationTest.class);
49 suite.setName("StandardDeviation Tests");
50 return suite;
51 }
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55
56 public double expectedValue() {
57 return this.std;
58 }
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63
64 public void testNaN() {
65 StandardDeviation std = new StandardDeviation();
66 assertTrue(Double.isNaN(std.getResult()));
67 std.increment(1d);
68 assertEquals(0d, std.getResult(), 0);
69 }
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74 public void testPopulation() {
75 double[] values = {-1.0d, 3.1d, 4.0d, -2.1d, 22d, 11.7d, 3d, 14d};
76 double sigma = populationStandardDeviation(values);
77 SecondMoment m = new SecondMoment();
78 m.evaluate(values);
79 StandardDeviation s1 = new StandardDeviation();
80 s1.setBiasCorrected(false);
81 assertEquals(sigma, s1.evaluate(values), 1E-14);
82 s1.incrementAll(values);
83 assertEquals(sigma, s1.getResult(), 1E-14);
84 s1 = new StandardDeviation(false, m);
85 assertEquals(sigma, s1.getResult(), 1E-14);
86 s1 = new StandardDeviation(false);
87 assertEquals(sigma, s1.evaluate(values), 1E-14);
88 s1.incrementAll(values);
89 assertEquals(sigma, s1.getResult(), 1E-14);
90 }
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95 protected double populationStandardDeviation(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 Math.sqrt(sum / (double) v.length);
102 }
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104 }