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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 StandardDeviationTest extends StorelessUnivariateStatisticAbstractTest{
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32 protected StandardDeviation stat;
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37 public StandardDeviationTest(String name) {
38 super(name);
39 }
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44 public UnivariateStatistic getUnivariateStatistic() {
45 return new StandardDeviation();
46 }
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48 public static Test suite() {
49 TestSuite suite = new TestSuite(StandardDeviationTest.class);
50 suite.setName("StandardDeviation Tests");
51 return suite;
52 }
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57 public double expectedValue() {
58 return this.std;
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 double sigma = populationStandardDeviation(values);
78 SecondMoment m = new SecondMoment();
79 m.evaluate(values);
80 StandardDeviation s1 = new StandardDeviation();
81 s1.setBiasCorrected(false);
82 assertEquals(sigma, s1.evaluate(values), 1E-14);
83 s1.incrementAll(values);
84 assertEquals(sigma, s1.getResult(), 1E-14);
85 s1 = new StandardDeviation(false, m);
86 assertEquals(sigma, s1.getResult(), 1E-14);
87 s1 = new StandardDeviation(false);
88 assertEquals(sigma, s1.evaluate(values), 1E-14);
89 s1.incrementAll(values);
90 assertEquals(sigma, s1.getResult(), 1E-14);
91 }
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96 protected double populationStandardDeviation(double[] v) {
97 double mean = new Mean().evaluate(v);
98 double sum = 0;
99 for (int i = 0; i < v.length; i++) {
100 sum += (v[i] - mean) * (v[i] - mean);
101 }
102 return Math.sqrt(sum / (double) v.length);
103 }
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105 }