1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.math.ode;
19  
20  import junit.framework.*;
21  import java.util.Random;
22  
23  import org.apache.commons.math.ode.ContinuousOutputModel;
24  import org.apache.commons.math.ode.DerivativeException;
25  import org.apache.commons.math.ode.DormandPrince54Integrator;
26  import org.apache.commons.math.ode.FirstOrderIntegrator;
27  import org.apache.commons.math.ode.IntegratorException;
28  
29  public class ContinuousOutputModelTest
30    extends TestCase {
31  
32    public ContinuousOutputModelTest(String name) {
33      super(name);
34      pb    = null;
35      integ = null;
36    }
37  
38    public void testBoundaries()
39      throws DerivativeException, IntegratorException {
40      integ.setStepHandler(new ContinuousOutputModel());
41      integ.integrate(pb,
42                      pb.getInitialTime(), pb.getInitialState(),
43                      pb.getFinalTime(), new double[pb.getDimension()]);
44      ContinuousOutputModel cm = (ContinuousOutputModel) integ.getStepHandler();
45      cm.setInterpolatedTime(2.0 * pb.getInitialTime() - pb.getFinalTime());
46      cm.setInterpolatedTime(2.0 * pb.getFinalTime() - pb.getInitialTime());
47      cm.setInterpolatedTime(0.5 * (pb.getFinalTime() + pb.getInitialTime()));
48    }
49  
50    public void testRandomAccess()
51      throws DerivativeException, IntegratorException {
52  
53      ContinuousOutputModel cm = new ContinuousOutputModel();
54      integ.setStepHandler(cm);
55      integ.integrate(pb,
56                      pb.getInitialTime(), pb.getInitialState(),
57                      pb.getFinalTime(), new double[pb.getDimension()]);
58  
59      Random random = new Random(347588535632l);
60      double maxError = 0.0;
61      for (int i = 0; i < 1000; ++i) {
62        double r = random.nextDouble();
63        double time = r * pb.getInitialTime() + (1.0 - r) * pb.getFinalTime();
64        cm.setInterpolatedTime(time);
65        double[] interpolatedY = cm.getInterpolatedState ();
66        double[] theoreticalY  = pb.computeTheoreticalState(time);
67        double dx = interpolatedY[0] - theoreticalY[0];
68        double dy = interpolatedY[1] - theoreticalY[1];
69        double error = dx * dx + dy * dy;
70        if (error > maxError) {
71          maxError = error;
72        }
73      }
74  
75      assertTrue(maxError < 1.0e-9);
76  
77    }
78  
79    public void testModelsMerging()
80      throws DerivativeException, IntegratorException {
81  
82        // theoretical solution: y[0] = cos(t), y[1] = sin(t)
83        FirstOrderDifferentialEquations problem =
84            new FirstOrderDifferentialEquations() {
85            public void computeDerivatives(double t, double[] y, double[] dot)
86            throws DerivativeException {
87                dot[0] = -y[1];
88                dot[1] =  y[0];
89            }
90            public int getDimension() {
91                return 2;
92            }
93        };
94  
95        // integrate backward from &pi; to 0;
96        ContinuousOutputModel cm1 = new ContinuousOutputModel();
97        FirstOrderIntegrator integ1 =
98            new DormandPrince853Integrator(0, 1.0, 1.0e-8, 1.0e-8);
99        integ1.setStepHandler(cm1);
100       integ1.integrate(problem, Math.PI, new double[] { -1.0, 0.0 },
101                        0, new double[2]);
102 
103       // integrate backward from 2&pi; to &pi;
104       ContinuousOutputModel cm2 = new ContinuousOutputModel();
105       FirstOrderIntegrator integ2 =
106           new DormandPrince853Integrator(0, 0.1, 1.0e-12, 1.0e-12);
107       integ2.setStepHandler(cm2);
108       integ2.integrate(problem, 2.0 * Math.PI, new double[] { 1.0, 0.0 },
109                        Math.PI, new double[2]);
110 
111       // merge the two half circles
112       ContinuousOutputModel cm = new ContinuousOutputModel();
113       cm.append(cm2);
114       cm.append(new ContinuousOutputModel());
115       cm.append(cm1);
116 
117       // check circle
118       assertEquals(2.0 * Math.PI, cm.getInitialTime(), 1.0e-12);
119       assertEquals(0, cm.getFinalTime(), 1.0e-12);
120       assertEquals(cm.getFinalTime(), cm.getInterpolatedTime(), 1.0e-12);
121       for (double t = 0; t < 2.0 * Math.PI; t += 0.1) {
122           cm.setInterpolatedTime(t);
123           double[] y = cm.getInterpolatedState();
124           assertEquals(Math.cos(t), y[0], 1.0e-7);
125           assertEquals(Math.sin(t), y[1], 1.0e-7);
126       }
127       
128   }
129 
130   public void testErrorConditions()
131     throws DerivativeException {
132 
133       ContinuousOutputModel cm = new ContinuousOutputModel();
134       cm.handleStep(buildInterpolator(0, new double[] { 0.0, 1.0, -2.0 }, 1), true);
135       
136       // dimension mismatch
137       assertTrue(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0 }, 2.0));
138 
139       // hole between time ranges
140       assertTrue(checkAppendError(cm, 10.0, new double[] { 0.0, 1.0, -2.0 }, 20.0));
141 
142       // propagation direction mismatch
143       assertTrue(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0, -2.0 }, 0.0));
144 
145       // no errors
146       assertFalse(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0, -2.0 }, 2.0));
147 
148   }
149 
150   private boolean checkAppendError(ContinuousOutputModel cm,
151                                    double t0, double[] y0, double t1)
152   throws DerivativeException {
153       try {
154           ContinuousOutputModel otherCm = new ContinuousOutputModel();
155           otherCm.handleStep(buildInterpolator(t0, y0, t1), true);
156           cm.append(otherCm);
157       } catch(IllegalArgumentException iae) {
158           //expected behavior
159           return true;
160       }
161       return false;
162   }
163 
164   private StepInterpolator buildInterpolator(double t0, double[] y0, double t1) {
165       DummyStepInterpolator interpolator  = new DummyStepInterpolator(y0, t1 >= t0);
166       interpolator.storeTime(t0);
167       interpolator.shift();
168       interpolator.storeTime(t1);
169       return interpolator;
170   }
171 
172   public void checkValue(double value, double reference) {
173     assertTrue(Math.abs(value - reference) < 1.0e-10);
174   }
175 
176   public static Test suite() {
177     return new TestSuite(ContinuousOutputModelTest.class);
178   }
179 
180   public void setUp() {
181     pb = new TestProblem3(0.9);
182     double minStep = 0;
183     double maxStep = pb.getFinalTime() - pb.getInitialTime();
184     integ = new DormandPrince54Integrator(minStep, maxStep, 1.0e-8, 1.0e-8);
185   }
186 
187   public void tearDown() {
188     pb    = null;
189     integ = null;
190   }
191 
192   TestProblem3 pb;
193   FirstOrderIntegrator integ;
194 
195 }