| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.math4.legacy.stat.descriptive.moment; |
| |
| import org.apache.commons.math4.legacy.stat.descriptive.StorelessUnivariateStatisticAbstractTest; |
| import org.apache.commons.math4.legacy.stat.descriptive.UnivariateStatistic; |
| import org.apache.commons.math4.legacy.core.jdkmath.AccurateMath; |
| import org.junit.Assert; |
| import org.junit.Test; |
| |
| /** |
| * Test cases for the {@link UnivariateStatistic} class. |
| * |
| */ |
| public class StandardDeviationTest extends StorelessUnivariateStatisticAbstractTest{ |
| |
| protected StandardDeviation stat; |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public UnivariateStatistic getUnivariateStatistic() { |
| return new StandardDeviation(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public double expectedValue() { |
| return this.std; |
| } |
| |
| /** |
| * Make sure Double.NaN is returned iff n = 0 |
| * |
| */ |
| @Test |
| public void testNaN() { |
| StandardDeviation std = new StandardDeviation(); |
| Assert.assertTrue(Double.isNaN(std.getResult())); |
| std.increment(1d); |
| Assert.assertEquals(0d, std.getResult(), 0); |
| } |
| |
| /** |
| * Test population version of variance |
| */ |
| @Test |
| public void testPopulation() { |
| double[] values = {-1.0d, 3.1d, 4.0d, -2.1d, 22d, 11.7d, 3d, 14d}; |
| double sigma = populationStandardDeviation(values); |
| SecondMoment m = new SecondMoment(); |
| m.incrementAll(values); // side effect is to add values |
| StandardDeviation s1 = new StandardDeviation(); |
| s1.setBiasCorrected(false); |
| Assert.assertEquals(sigma, s1.evaluate(values), 1E-14); |
| s1.incrementAll(values); |
| Assert.assertEquals(sigma, s1.getResult(), 1E-14); |
| s1 = new StandardDeviation(false, m); |
| Assert.assertEquals(sigma, s1.getResult(), 1E-14); |
| s1 = new StandardDeviation(false); |
| Assert.assertEquals(sigma, s1.evaluate(values), 1E-14); |
| s1.incrementAll(values); |
| Assert.assertEquals(sigma, s1.getResult(), 1E-14); |
| } |
| |
| /** |
| * Definitional formula for population standard deviation |
| */ |
| protected double populationStandardDeviation(double[] v) { |
| double mean = new Mean().evaluate(v); |
| double sum = 0; |
| for (int i = 0; i < v.length; i++) { |
| sum += (v[i] - mean) * (v[i] - mean); |
| } |
| return AccurateMath.sqrt(sum / v.length); |
| } |
| |
| } |