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.FirstOrderIntegrator;
26  import org.apache.commons.math.ode.IntegratorException;
27  import org.apache.commons.math.ode.nonstiff.DormandPrince54Integrator;
28  import org.apache.commons.math.ode.nonstiff.DormandPrince853Integrator;
29  import org.apache.commons.math.ode.sampling.DummyStepInterpolator;
30  import org.apache.commons.math.ode.sampling.StepInterpolator;
31  
32  public class ContinuousOutputModelTest
33    extends TestCase {
34  
35    public ContinuousOutputModelTest(String name) {
36      super(name);
37      pb    = null;
38      integ = null;
39    }
40  
41    public void testBoundaries()
42      throws DerivativeException, IntegratorException {
43      integ.addStepHandler(new ContinuousOutputModel());
44      integ.integrate(pb,
45                      pb.getInitialTime(), pb.getInitialState(),
46                      pb.getFinalTime(), new double[pb.getDimension()]);
47      ContinuousOutputModel cm = (ContinuousOutputModel) integ.getStepHandlers().iterator().next();
48      cm.setInterpolatedTime(2.0 * pb.getInitialTime() - pb.getFinalTime());
49      cm.setInterpolatedTime(2.0 * pb.getFinalTime() - pb.getInitialTime());
50      cm.setInterpolatedTime(0.5 * (pb.getFinalTime() + pb.getInitialTime()));
51    }
52  
53    public void testRandomAccess()
54      throws DerivativeException, IntegratorException {
55  
56      ContinuousOutputModel cm = new ContinuousOutputModel();
57      integ.addStepHandler(cm);
58      integ.integrate(pb,
59                      pb.getInitialTime(), pb.getInitialState(),
60                      pb.getFinalTime(), new double[pb.getDimension()]);
61  
62      Random random = new Random(347588535632l);
63      double maxError = 0.0;
64      for (int i = 0; i < 1000; ++i) {
65        double r = random.nextDouble();
66        double time = r * pb.getInitialTime() + (1.0 - r) * pb.getFinalTime();
67        cm.setInterpolatedTime(time);
68        double[] interpolatedY = cm.getInterpolatedState ();
69        double[] theoreticalY  = pb.computeTheoreticalState(time);
70        double dx = interpolatedY[0] - theoreticalY[0];
71        double dy = interpolatedY[1] - theoreticalY[1];
72        double error = dx * dx + dy * dy;
73        if (error > maxError) {
74          maxError = error;
75        }
76      }
77  
78      assertTrue(maxError < 1.0e-9);
79  
80    }
81  
82    public void testModelsMerging()
83      throws DerivativeException, IntegratorException {
84  
85        // theoretical solution: y[0] = cos(t), y[1] = sin(t)
86        FirstOrderDifferentialEquations problem =
87            new FirstOrderDifferentialEquations() {
88                private static final long serialVersionUID = 2472449657345878299L;
89                public void computeDerivatives(double t, double[] y, double[] dot)
90                    throws DerivativeException {
91                    dot[0] = -y[1];
92                    dot[1] =  y[0];
93                }
94                public int getDimension() {
95                    return 2;
96                }
97            };
98  
99        // integrate backward from &pi; to 0;
100       ContinuousOutputModel cm1 = new ContinuousOutputModel();
101       FirstOrderIntegrator integ1 =
102           new DormandPrince853Integrator(0, 1.0, 1.0e-8, 1.0e-8);
103       integ1.addStepHandler(cm1);
104       integ1.integrate(problem, Math.PI, new double[] { -1.0, 0.0 },
105                        0, new double[2]);
106 
107       // integrate backward from 2&pi; to &pi;
108       ContinuousOutputModel cm2 = new ContinuousOutputModel();
109       FirstOrderIntegrator integ2 =
110           new DormandPrince853Integrator(0, 0.1, 1.0e-12, 1.0e-12);
111       integ2.addStepHandler(cm2);
112       integ2.integrate(problem, 2.0 * Math.PI, new double[] { 1.0, 0.0 },
113                        Math.PI, new double[2]);
114 
115       // merge the two half circles
116       ContinuousOutputModel cm = new ContinuousOutputModel();
117       cm.append(cm2);
118       cm.append(new ContinuousOutputModel());
119       cm.append(cm1);
120 
121       // check circle
122       assertEquals(2.0 * Math.PI, cm.getInitialTime(), 1.0e-12);
123       assertEquals(0, cm.getFinalTime(), 1.0e-12);
124       assertEquals(cm.getFinalTime(), cm.getInterpolatedTime(), 1.0e-12);
125       for (double t = 0; t < 2.0 * Math.PI; t += 0.1) {
126           cm.setInterpolatedTime(t);
127           double[] y = cm.getInterpolatedState();
128           assertEquals(Math.cos(t), y[0], 1.0e-7);
129           assertEquals(Math.sin(t), y[1], 1.0e-7);
130       }
131       
132   }
133 
134   public void testErrorConditions()
135     throws DerivativeException {
136 
137       ContinuousOutputModel cm = new ContinuousOutputModel();
138       cm.handleStep(buildInterpolator(0, new double[] { 0.0, 1.0, -2.0 }, 1), true);
139       
140       // dimension mismatch
141       assertTrue(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0 }, 2.0));
142 
143       // hole between time ranges
144       assertTrue(checkAppendError(cm, 10.0, new double[] { 0.0, 1.0, -2.0 }, 20.0));
145 
146       // propagation direction mismatch
147       assertTrue(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0, -2.0 }, 0.0));
148 
149       // no errors
150       assertFalse(checkAppendError(cm, 1.0, new double[] { 0.0, 1.0, -2.0 }, 2.0));
151 
152   }
153 
154   private boolean checkAppendError(ContinuousOutputModel cm,
155                                    double t0, double[] y0, double t1)
156   throws DerivativeException {
157       try {
158           ContinuousOutputModel otherCm = new ContinuousOutputModel();
159           otherCm.handleStep(buildInterpolator(t0, y0, t1), true);
160           cm.append(otherCm);
161       } catch(IllegalArgumentException iae) {
162           //expected behavior
163           return true;
164       }
165       return false;
166   }
167 
168   private StepInterpolator buildInterpolator(double t0, double[] y0, double t1) {
169       DummyStepInterpolator interpolator  = new DummyStepInterpolator(y0, t1 >= t0);
170       interpolator.storeTime(t0);
171       interpolator.shift();
172       interpolator.storeTime(t1);
173       return interpolator;
174   }
175 
176   public void checkValue(double value, double reference) {
177     assertTrue(Math.abs(value - reference) < 1.0e-10);
178   }
179 
180   public static Test suite() {
181     return new TestSuite(ContinuousOutputModelTest.class);
182   }
183 
184   @Override
185   public void setUp() {
186     pb = new TestProblem3(0.9);
187     double minStep = 0;
188     double maxStep = pb.getFinalTime() - pb.getInitialTime();
189     integ = new DormandPrince54Integrator(minStep, maxStep, 1.0e-8, 1.0e-8);
190   }
191 
192   @Override
193   public void tearDown() {
194     pb    = null;
195     integ = null;
196   }
197 
198   TestProblem3 pb;
199   FirstOrderIntegrator integ;
200 
201 }