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18 package org.apache.commons.math.ode;
19
20 import junit.framework.*;
21 import java.util.Random;
22 import java.io.ByteArrayOutputStream;
23 import java.io.ByteArrayInputStream;
24 import java.io.ObjectOutputStream;
25 import java.io.ObjectInputStream;
26 import java.io.IOException;
27
28 import org.apache.commons.math.ode.ContinuousOutputModel;
29 import org.apache.commons.math.ode.DerivativeException;
30 import org.apache.commons.math.ode.EulerIntegrator;
31 import org.apache.commons.math.ode.EulerStepInterpolator;
32 import org.apache.commons.math.ode.FirstOrderDifferentialEquations;
33 import org.apache.commons.math.ode.IntegratorException;
34
35 public class EulerStepInterpolatorTest
36 extends TestCase {
37
38 public EulerStepInterpolatorTest(String name) {
39 super(name);
40 }
41
42 public void testNoReset() {
43
44 double[] y = { 0.0, 1.0, -2.0 };
45 double[][] yDot = { { 1.0, 2.0, -2.0 } };
46 EulerStepInterpolator interpolator = new EulerStepInterpolator();
47 interpolator.reinitialize(new DummyEquations(), y, yDot, true);
48 interpolator.storeTime(0);
49 interpolator.shift();
50 interpolator.storeTime(1);
51
52 double[] result = interpolator.getInterpolatedState();
53 for (int i = 0; i < result.length; ++i) {
54 assertTrue(Math.abs(result[i] - y[i]) < 1.0e-10);
55 }
56
57 }
58
59 public void testInterpolationAtBounds()
60 throws DerivativeException {
61
62 double t0 = 0;
63 double[] y0 = {0.0, 1.0, -2.0};
64
65 double[] y = (double[]) y0.clone();
66 double[][] yDot = { new double[y0.length] };
67 EulerStepInterpolator interpolator = new EulerStepInterpolator();
68 interpolator.reinitialize(new DummyEquations(), y, yDot, true);
69 interpolator.storeTime(t0);
70
71 double dt = 1.0;
72 y[0] = 1.0;
73 y[1] = 3.0;
74 y[2] = -4.0;
75 yDot[0][0] = (y[0] - y0[0]) / dt;
76 yDot[0][1] = (y[1] - y0[1]) / dt;
77 yDot[0][2] = (y[2] - y0[2]) / dt;
78 interpolator.shift();
79 interpolator.storeTime(t0 + dt);
80
81 interpolator.setInterpolatedTime(interpolator.getPreviousTime());
82 double[] result = interpolator.getInterpolatedState();
83 for (int i = 0; i < result.length; ++i) {
84 assertTrue(Math.abs(result[i] - y0[i]) < 1.0e-10);
85 }
86
87 interpolator.setInterpolatedTime(interpolator.getCurrentTime());
88 result = interpolator.getInterpolatedState();
89 for (int i = 0; i < result.length; ++i) {
90 assertTrue(Math.abs(result[i] - y[i]) < 1.0e-10);
91 }
92
93 }
94
95 public void testInterpolationInside()
96 throws DerivativeException {
97
98 double[] y = { 1.0, 3.0, -4.0 };
99 double[][] yDot = { { 1.0, 2.0, -2.0 } };
100 EulerStepInterpolator interpolator = new EulerStepInterpolator();
101 interpolator.reinitialize(new DummyEquations(), y, yDot, true);
102 interpolator.storeTime(0);
103 interpolator.shift();
104 interpolator.storeTime(1);
105
106 interpolator.setInterpolatedTime(0.1);
107 double[] result = interpolator.getInterpolatedState();
108 assertTrue(Math.abs(result[0] - 0.1) < 1.0e-10);
109 assertTrue(Math.abs(result[1] - 1.2) < 1.0e-10);
110 assertTrue(Math.abs(result[2] + 2.2) < 1.0e-10);
111
112 interpolator.setInterpolatedTime(0.5);
113 result = interpolator.getInterpolatedState();
114 assertTrue(Math.abs(result[0] - 0.5) < 1.0e-10);
115 assertTrue(Math.abs(result[1] - 2.0) < 1.0e-10);
116 assertTrue(Math.abs(result[2] + 3.0) < 1.0e-10);
117
118 }
119
120 public void testSerialization()
121 throws DerivativeException, IntegratorException,
122 IOException, ClassNotFoundException {
123
124 TestProblem1 pb = new TestProblem1();
125 double step = (pb.getFinalTime() - pb.getInitialTime()) * 0.001;
126 EulerIntegrator integ = new EulerIntegrator(step);
127 integ.setStepHandler(new ContinuousOutputModel());
128 integ.integrate(pb,
129 pb.getInitialTime(), pb.getInitialState(),
130 pb.getFinalTime(), new double[pb.getDimension()]);
131
132 ByteArrayOutputStream bos = new ByteArrayOutputStream();
133 ObjectOutputStream oos = new ObjectOutputStream(bos);
134 oos.writeObject(integ.getStepHandler());
135
136 assertTrue(bos.size () > 82000);
137 assertTrue(bos.size () < 83000);
138
139 ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
140 ObjectInputStream ois = new ObjectInputStream(bis);
141 ContinuousOutputModel cm = (ContinuousOutputModel) ois.readObject();
142
143 Random random = new Random(347588535632l);
144 double maxError = 0.0;
145 for (int i = 0; i < 1000; ++i) {
146 double r = random.nextDouble();
147 double time = r * pb.getInitialTime() + (1.0 - r) * pb.getFinalTime();
148 cm.setInterpolatedTime(time);
149 double[] interpolatedY = cm.getInterpolatedState ();
150 double[] theoreticalY = pb.computeTheoreticalState(time);
151 double dx = interpolatedY[0] - theoreticalY[0];
152 double dy = interpolatedY[1] - theoreticalY[1];
153 double error = dx * dx + dy * dy;
154 if (error > maxError) {
155 maxError = error;
156 }
157 }
158
159 assertTrue(maxError < 0.001);
160
161 }
162
163 private static class DummyEquations
164 implements FirstOrderDifferentialEquations {
165 public int getDimension() {
166 return 0;
167 }
168 public void computeDerivatives(double t, double[] y, double[] yDot) {
169 }
170 }
171
172 public static Test suite() {
173 return new TestSuite(EulerStepInterpolatorTest.class);
174 }
175
176 }