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Java example source code file (FirstOrderConverterTest.java)

This example Java source code file (FirstOrderConverterTest.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

classicalrungekuttaintegrator, dimensionmismatchexception, equations, firstorderconverter, firstorderconvertertest, maxcountexceededexception, nobracketingexception, numberistoosmallexception, secondorderdifferentialequations, test

The FirstOrderConverterTest.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.ode;

import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.exception.NoBracketingException;
import org.apache.commons.math3.exception.NumberIsTooSmallException;
import org.apache.commons.math3.ode.nonstiff.ClassicalRungeKuttaIntegrator;
import org.apache.commons.math3.util.FastMath;
import org.junit.Assert;
import org.junit.Test;


public class FirstOrderConverterTest {

  @Test
  public void testDoubleDimension() {
    for (int i = 1; i < 10; ++i) {
      SecondOrderDifferentialEquations eqn2 = new Equations(i, 0.2);
      FirstOrderConverter eqn1 = new FirstOrderConverter(eqn2);
      Assert.assertTrue(eqn1.getDimension() == (2 * eqn2.getDimension()));
    }
  }

  @Test
  public void testDecreasingSteps()
      throws DimensionMismatchException, NumberIsTooSmallException, MaxCountExceededException, NoBracketingException {

    double previousError = Double.NaN;
    for (int i = 0; i < 10; ++i) {

      double step  = FastMath.pow(2.0, -(i + 1));
      double error = integrateWithSpecifiedStep(4.0, 0.0, 1.0, step)
                   - FastMath.sin(4.0);
      if (i > 0) {
        Assert.assertTrue(FastMath.abs(error) < FastMath.abs(previousError));
      }
      previousError = error;

    }
  }

  @Test
  public void testSmallStep()
      throws DimensionMismatchException, NumberIsTooSmallException, MaxCountExceededException, NoBracketingException {
    double error = integrateWithSpecifiedStep(4.0, 0.0, 1.0, 1.0e-4)
                   - FastMath.sin(4.0);
    Assert.assertTrue(FastMath.abs(error) < 1.0e-10);
  }

  @Test
  public void testBigStep()
      throws DimensionMismatchException, NumberIsTooSmallException, MaxCountExceededException, NoBracketingException {
    double error = integrateWithSpecifiedStep(4.0, 0.0, 1.0, 0.5)
                   - FastMath.sin(4.0);
    Assert.assertTrue(FastMath.abs(error) > 0.1);
  }

  private static class Equations
    implements SecondOrderDifferentialEquations {

     private int n;

      private double omega2;

      public Equations(int n, double omega) {
        this.n = n;
        omega2 = omega * omega;
      }

      public int getDimension() {
        return n;
      }

      public void computeSecondDerivatives(double t, double[] y, double[] yDot,
                                           double[] yDDot) {
        for (int i = 0; i < n; ++i) {
          yDDot[i] = -omega2 * y[i];
        }
    }

  }

  private double integrateWithSpecifiedStep(double omega,
                                            double t0, double t,
                                            double step) throws DimensionMismatchException, NumberIsTooSmallException, MaxCountExceededException, NoBracketingException {
    double[] y0 = new double[2];
    y0[0] = FastMath.sin(omega * t0);
    y0[1] = omega * FastMath.cos(omega * t0);
    ClassicalRungeKuttaIntegrator i = new ClassicalRungeKuttaIntegrator(step);
    double[] y = new double[2];
    i.integrate(new FirstOrderConverter(new Equations(1, omega)), t0, y0, t, y);
    return y[0];
  }

}

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