001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 * http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017
018 package org.apache.commons.math.ode.nonstiff;
019
020 import static org.junit.Assert.assertTrue;
021
022 import java.io.ByteArrayInputStream;
023 import java.io.ByteArrayOutputStream;
024 import java.io.IOException;
025 import java.io.ObjectInputStream;
026 import java.io.ObjectOutputStream;
027 import java.util.Random;
028
029 import org.apache.commons.math.ode.ContinuousOutputModel;
030 import org.apache.commons.math.ode.DerivativeException;
031 import org.apache.commons.math.ode.IntegratorException;
032 import org.apache.commons.math.ode.TestProblem1;
033 import org.apache.commons.math.ode.TestProblem3;
034 import org.apache.commons.math.ode.sampling.StepHandler;
035 import org.apache.commons.math.ode.sampling.StepInterpolatorTestUtils;
036 import org.junit.Test;
037
038 public class EulerStepInterpolatorTest {
039
040 @Test
041 public void noReset() throws DerivativeException {
042
043 double[] y = { 0.0, 1.0, -2.0 };
044 double[][] yDot = { { 1.0, 2.0, -2.0 } };
045 EulerStepInterpolator interpolator = new EulerStepInterpolator();
046 interpolator.reinitialize(new DummyIntegrator(interpolator), y, yDot, true);
047 interpolator.storeTime(0);
048 interpolator.shift();
049 interpolator.storeTime(1);
050
051 double[] result = interpolator.getInterpolatedState();
052 for (int i = 0; i < result.length; ++i) {
053 assertTrue(Math.abs(result[i] - y[i]) < 1.0e-10);
054 }
055
056 }
057
058 @Test
059 public void interpolationAtBounds()
060 throws DerivativeException {
061
062 double t0 = 0;
063 double[] y0 = {0.0, 1.0, -2.0};
064
065 double[] y = y0.clone();
066 double[][] yDot = { new double[y0.length] };
067 EulerStepInterpolator interpolator = new EulerStepInterpolator();
068 interpolator.reinitialize(new DummyIntegrator(interpolator), y, yDot, true);
069 interpolator.storeTime(t0);
070
071 double dt = 1.0;
072 y[0] = 1.0;
073 y[1] = 3.0;
074 y[2] = -4.0;
075 yDot[0][0] = (y[0] - y0[0]) / dt;
076 yDot[0][1] = (y[1] - y0[1]) / dt;
077 yDot[0][2] = (y[2] - y0[2]) / dt;
078 interpolator.shift();
079 interpolator.storeTime(t0 + dt);
080
081 interpolator.setInterpolatedTime(interpolator.getPreviousTime());
082 double[] result = interpolator.getInterpolatedState();
083 for (int i = 0; i < result.length; ++i) {
084 assertTrue(Math.abs(result[i] - y0[i]) < 1.0e-10);
085 }
086
087 interpolator.setInterpolatedTime(interpolator.getCurrentTime());
088 result = interpolator.getInterpolatedState();
089 for (int i = 0; i < result.length; ++i) {
090 assertTrue(Math.abs(result[i] - y[i]) < 1.0e-10);
091 }
092
093 }
094
095 @Test
096 public void interpolationInside()
097 throws DerivativeException {
098
099 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 }