/*
* 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);
}
public static Test suite() {
return new TestSuite(FirstOrderConverterTest.class);
}
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];
}
}