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18 package org.apache.commons.math.ode.nonstiff;
19
20 import static org.junit.Assert.assertTrue;
21
22 import java.io.ByteArrayInputStream;
23 import java.io.ByteArrayOutputStream;
24 import java.io.IOException;
25 import java.io.ObjectInputStream;
26 import java.io.ObjectOutputStream;
27 import java.util.Random;
28
29 import org.apache.commons.math.ode.ContinuousOutputModel;
30 import org.apache.commons.math.ode.DerivativeException;
31 import org.apache.commons.math.ode.IntegratorException;
32 import org.apache.commons.math.ode.TestProblem1;
33 import org.apache.commons.math.ode.TestProblem3;
34 import org.apache.commons.math.ode.sampling.StepHandler;
35 import org.apache.commons.math.ode.sampling.StepInterpolatorTestUtils;
36 import org.junit.Test;
37
38 public class EulerStepInterpolatorTest {
39
40 @Test
41 public void noReset() throws DerivativeException {
42
43 double[] y = { 0.0, 1.0, -2.0 };
44 double[][] yDot = { { 1.0, 2.0, -2.0 } };
45 EulerStepInterpolator interpolator = new EulerStepInterpolator();
46 interpolator.reinitialize(new DummyIntegrator(interpolator), y, yDot, true);
47 interpolator.storeTime(0);
48 interpolator.shift();
49 interpolator.storeTime(1);
50
51 double[] result = interpolator.getInterpolatedState();
52 for (int i = 0; i < result.length; ++i) {
53 assertTrue(Math.abs(result[i] - y[i]) < 1.0e-10);
54 }
55
56 }
57
58 @Test
59 public void interpolationAtBounds()
60 throws DerivativeException {
61
62 double t0 = 0;
63 double[] y0 = {0.0, 1.0, -2.0};
64
65 double[] y = y0.clone();
66 double[][] yDot = { new double[y0.length] };
67 EulerStepInterpolator interpolator = new EulerStepInterpolator();
68 interpolator.reinitialize(new DummyIntegrator(interpolator), 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 @Test
96 public void interpolationInside()
97 throws DerivativeException {
98
99 double[] y = { 1.0, 3.0, -4.0 };
100 double[][] yDot = { { 1.0, 2.0, -2.0 } };
101 EulerStepInterpolator interpolator = new EulerStepInterpolator();
102 interpolator.reinitialize(new DummyIntegrator(interpolator), y, yDot, true);
103 interpolator.storeTime(0);
104 interpolator.shift();
105 interpolator.storeTime(1);
106
107 interpolator.setInterpolatedTime(0.1);
108 double[] result = interpolator.getInterpolatedState();
109 assertTrue(Math.abs(result[0] - 0.1) < 1.0e-10);
110 assertTrue(Math.abs(result[1] - 1.2) < 1.0e-10);
111 assertTrue(Math.abs(result[2] + 2.2) < 1.0e-10);
112
113 interpolator.setInterpolatedTime(0.5);
114 result = interpolator.getInterpolatedState();
115 assertTrue(Math.abs(result[0] - 0.5) < 1.0e-10);
116 assertTrue(Math.abs(result[1] - 2.0) < 1.0e-10);
117 assertTrue(Math.abs(result[2] + 3.0) < 1.0e-10);
118
119 }
120
121 @Test
122 public void derivativesConsistency()
123 throws DerivativeException, IntegratorException {
124 TestProblem3 pb = new TestProblem3();
125 double step = (pb.getFinalTime() - pb.getInitialTime()) * 0.001;
126 EulerIntegrator integ = new EulerIntegrator(step);
127 StepInterpolatorTestUtils.checkDerivativesConsistency(integ, pb, 1.0e-10);
128 }
129
130 @Test
131 public void serialization()
132 throws DerivativeException, IntegratorException,
133 IOException, ClassNotFoundException {
134
135 TestProblem1 pb = new TestProblem1();
136 double step = (pb.getFinalTime() - pb.getInitialTime()) * 0.001;
137 EulerIntegrator integ = new EulerIntegrator(step);
138 integ.addStepHandler(new ContinuousOutputModel());
139 integ.integrate(pb,
140 pb.getInitialTime(), pb.getInitialState(),
141 pb.getFinalTime(), new double[pb.getDimension()]);
142
143 ByteArrayOutputStream bos = new ByteArrayOutputStream();
144 ObjectOutputStream oos = new ObjectOutputStream(bos);
145 for (StepHandler handler : integ.getStepHandlers()) {
146 oos.writeObject(handler);
147 }
148
149 ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
150 ObjectInputStream ois = new ObjectInputStream(bis);
151 ContinuousOutputModel cm = (ContinuousOutputModel) ois.readObject();
152
153 Random random = new Random(347588535632l);
154 double maxError = 0.0;
155 for (int i = 0; i < 1000; ++i) {
156 double r = random.nextDouble();
157 double time = r * pb.getInitialTime() + (1.0 - r) * pb.getFinalTime();
158 cm.setInterpolatedTime(time);
159 double[] interpolatedY = cm.getInterpolatedState ();
160 double[] theoreticalY = pb.computeTheoreticalState(time);
161 double dx = interpolatedY[0] - theoreticalY[0];
162 double dy = interpolatedY[1] - theoreticalY[1];
163 double error = dx * dx + dy * dy;
164 if (error > maxError) {
165 maxError = error;
166 }
167 }
168 assertTrue(maxError < 0.001);
169
170 }
171
172 private static class DummyIntegrator extends RungeKuttaIntegrator {
173
174
175 protected DummyIntegrator(RungeKuttaStepInterpolator prototype) {
176 super("dummy", new double[0], new double[0][0], new double[0], prototype, Double.NaN);
177 }
178
179 }
180
181 }