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Java example source code file (StandardDeviationTest.java)

This example Java source code file (StandardDeviationTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

override, secondmoment, standarddeviation, standarddeviationtest, storelessunivariatestatisticabstracttest, test, univariatestatistic

The StandardDeviationTest.java Java example source code

/*
 * 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.math3.stat.descriptive.moment;

import org.apache.commons.math3.stat.descriptive.StorelessUnivariateStatisticAbstractTest;
import org.apache.commons.math3.stat.descriptive.UnivariateStatistic;
import org.apache.commons.math3.util.FastMath;
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.evaluate(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 FastMath.sqrt(sum / v.length);
    }

}

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