Commons Math example source code file (FirstOrderConverterTest.java)

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

Java - Commons Math tags/keywords

classicalrungekuttaintegrator, derivativeexception, derivativeexception, equations, equations, firstorderconverter, firstorderconverter, firstorderconvertertest, integratorexception, integratorexception, secondorderdifferentialequations, testcase

The Commons Math FirstOrderConverterTest.java 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.math.ode;

import org.apache.commons.math.ode.DerivativeException;
import org.apache.commons.math.ode.FirstOrderConverter;
import org.apache.commons.math.ode.IntegratorException;
import org.apache.commons.math.ode.SecondOrderDifferentialEquations;
import org.apache.commons.math.ode.nonstiff.ClassicalRungeKuttaIntegrator;

import junit.framework.*;

public class FirstOrderConverterTest
  extends TestCase {

  public FirstOrderConverterTest(String name) {
    super(name);
  }

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

  public void testDecreasingSteps()
    throws DerivativeException, IntegratorException {

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

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

    }
  }

  public void testSmallStep()
    throws DerivativeException, IntegratorException {
    double error = integrateWithSpecifiedStep(4.0, 0.0, 1.0, 1.0e-4)
                   - Math.sin(4.0);
    assertTrue(Math.abs(error) < 1.0e-10);
  }

  public void testBigStep()
    throws DerivativeException, IntegratorException {
    double error = integrateWithSpecifiedStep(4.0, 0.0, 1.0, 0.5)
                   - Math.sin(4.0);
    assertTrue(Math.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 DerivativeException, IntegratorException {
    double[] y0 = new double[2];
    y0[0] = Math.sin(omega * t0);
    y0[1] = omega * Math.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];
  }

}