BAEL 767 - Introduction to Apache Commons Math (update) (#1670)

* BAEL 767 - Introduction to apache commons math

* BAEL 767 - Moving examples to test classes

* BAEL 767 - Renaming tests with BDD convention

apache-commons-math/pom.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.baeldung</groupId>
+    <artifactId>apache-commons-math</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven-compiler-plugin.version>3.6.0</maven-compiler-plugin.version>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-math3</artifactId>
+            <version>3.6.1</version>
+        </dependency>
+
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    
+</project>

apache-commons-math/src/test/java/com/baeldung/commons/math/ComplexTests.java

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+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.complex.Complex;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class ComplexTests {
+
+    @Test
+    public void whenComplexPow_thenCorrect() {
+        Complex first  = new Complex(1.0, 3.0);
+        Complex second = new Complex(2.0, 5.0);
+
+        Complex power = first.pow(second);
+
+        Assert.assertEquals(-0.007563724861696302, power.getReal(), 1e-7);
+        Assert.assertEquals(0.01786136835085382, power.getImaginary(), 1e-7);
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/FractionTests.java

@@ -0,0 +1,20 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.fraction.Fraction;
+import org.apache.commons.math3.fraction.FractionFormat;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class FractionTests {
+
+    @Test
+    public void whenFractionAdd_thenCorrect() {
+        Fraction lhs = new Fraction(1, 3);
+        Fraction rhs = new Fraction(2, 5);
+        Fraction sum = lhs.add(rhs);
+
+        Assert.assertEquals(11, sum.getNumerator());
+        Assert.assertEquals(15, sum.getDenominator());
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/GeometryTests.java

@@ -0,0 +1,21 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.geometry.euclidean.twod.Line;
+import org.apache.commons.math3.geometry.euclidean.twod.Vector2D;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class GeometryTests {
+
+    @Test
+    public void whenLineIntersection_thenCorrect() {
+        Line l1 = new Line(new Vector2D(0, 0), new Vector2D(1, 1), 0);
+        Line l2 = new Line(new Vector2D(0, 1), new Vector2D(1, 1.5), 0);
+
+        Vector2D intersection = l1.intersection(l2);
+
+        Assert.assertEquals(2, intersection.getX(), 1e-7);
+        Assert.assertEquals(2, intersection.getY(), 1e-7);
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/IntegrationTests.java

@@ -0,0 +1,21 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.analysis.UnivariateFunction;
+import org.apache.commons.math3.analysis.integration.SimpsonIntegrator;
+import org.apache.commons.math3.analysis.integration.UnivariateIntegrator;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class IntegrationTests {
+
+    @Test
+    public void whenUnivariateIntegratorIntegrate_thenCorrect() {
+        final UnivariateFunction function = v -> v;
+        final UnivariateIntegrator integrator = new SimpsonIntegrator(1.0e-12, 1.0e-8, 1, 32);
+
+        final double i = integrator.integrate(100, function, 0, 10);
+
+        Assert.assertEquals(16 + 2d/3d, i, 1e-7);
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/LinearAlgebraTests.java

@@ -0,0 +1,25 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.linear.*;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class LinearAlgebraTests {
+
+    @Test
+    public void whenDecompositionSolverSolve_thenCorrect() {
+        RealMatrix a =
+                new Array2DRowRealMatrix(new double[][] { { 2, 3, -2 }, { -1, 7, 6 }, { 4, -3, -5 } },
+                        false);
+        RealVector b = new ArrayRealVector(new double[] { 1, -2, 1 }, false);
+
+        DecompositionSolver solver = new LUDecomposition(a).getSolver();
+
+        RealVector solution = solver.solve(b);
+
+        Assert.assertEquals(-0.3698630137, solution.getEntry(0), 1e-7);
+        Assert.assertEquals(0.1780821918, solution.getEntry(1), 1e-7);
+        Assert.assertEquals(-0.602739726, solution.getEntry(2), 1e-7);
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/ProbabilitiesTests.java

@@ -0,0 +1,15 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.distribution.NormalDistribution;
+import org.junit.Test;
+
+public class ProbabilitiesTests {
+
+    @Test
+    public void whenNormalDistributionSample_thenSuccess() {
+        final NormalDistribution normalDistribution = new NormalDistribution(10, 3);
+
+        System.out.println(normalDistribution.sample());
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/RootFindingTests.java

@@ -0,0 +1,20 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.analysis.UnivariateFunction;
+import org.apache.commons.math3.analysis.solvers.BracketingNthOrderBrentSolver;
+import org.apache.commons.math3.analysis.solvers.UnivariateSolver;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class RootFindingTests {
+
+    @Test
+    public void whenUnivariateSolverSolver_thenCorrect() {
+        final UnivariateFunction function = v -> Math.pow(v, 2) - 2;
+        UnivariateSolver solver = new BracketingNthOrderBrentSolver(1.0e-12, 1.0e-8, 5);
+        double c = solver.solve(100, function, -10.0, 10.0, 0);
+
+        Assert.assertEquals(-Math.sqrt(2), c, 1e-7);
+    }
+
+}

apache-commons-math/src/test/java/com/baeldung/commons/math/StatisticsTests.java

@@ -0,0 +1,38 @@
+package com.baeldung.commons.math;
+
+import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+public class StatisticsTests {
+
+    private double[] values;
+    private DescriptiveStatistics descriptiveStatistics;
+
+    @Before
+    public void setUp() {
+        values = new double[] {65, 51 , 16, 11 , 6519, 191 ,0 , 98, 19854, 1, 32};
+
+        descriptiveStatistics = new DescriptiveStatistics();
+        for(double v : values) {
+            descriptiveStatistics.addValue(v);
+        }
+    }
+
+    @Test
+    public void whenDescriptiveStatisticsGetMean_thenCorrect() {
+        Assert.assertEquals(2439.8181818181815, descriptiveStatistics.getMean(), 1e-7);
+    }
+
+    @Test
+    public void whenDescriptiveStatisticsGetMedian_thenCorrect() {
+        Assert.assertEquals(51, descriptiveStatistics.getPercentile(50), 1e-7);
+    }
+
+    @Test
+    public void whenDescriptiveStatisticsGetStandardDeviation_thenCorrect() {
+        Assert.assertEquals(6093.054649651221, descriptiveStatistics.getStandardDeviation(), 1e-7);
+    }
+
+}