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Java example source code file (TestFieldProblem4.java)
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The TestFieldProblem4.java Java example source code
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.math3.ode;
import java.lang.reflect.Array;
import org.apache.commons.math3.Field;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.ode.events.Action;
import org.apache.commons.math3.ode.events.FieldEventHandler;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathArrays;
/**
* This class is used in the junit tests for the ODE integrators.
* <p>This specific problem is the following differential equation :
* <pre>
* x'' = -x
* </pre>
* And when x decreases down to 0, the state should be changed as follows :
* <pre>
* x' -> -x'
* </pre>
* The theoretical solution of this problem is x = |sin(t+a)|
* </p>
* @param <T> the type of the field elements
*/
public class TestFieldProblem4<T extends RealFieldElement
extends TestFieldProblemAbstract<T> {
/** Time offset. */
private T a;
/** Simple constructor.
* @param field field to which elements belong
*/
public TestFieldProblem4(Field<T> field) {
super(field);
a = convert(1.2);
T[] y0 = MathArrays.buildArray(field, 2);
y0[0] = a.sin();
y0[1] = a.cos();;
setInitialConditions(convert(0.0), y0);
setFinalConditions(convert(15));
setErrorScale(convert(1.0, 0.0));
}
@Override
public FieldEventHandler<T>[] getEventsHandlers() {
@SuppressWarnings("unchecked")
FieldEventHandler<T>[] handlers =
(FieldEventHandler<T>[]) Array.newInstance(FieldEventHandler.class, 2);
handlers[0] = new Bounce<T>();
handlers[1] = new Stop<T>();
return handlers;
}
/**
* Get the theoretical events times.
* @return theoretical events times
*/
@Override
public T[] getTheoreticalEventsTimes() {
T[] array = MathArrays.buildArray(getField(), 5);
array[0] = a.negate().add(1 * FastMath.PI);
array[1] = a.negate().add(2 * FastMath.PI);
array[2] = a.negate().add(3 * FastMath.PI);
array[3] = a.negate().add(4 * FastMath.PI);
array[4] = convert(120.0);
return array;
}
@Override
public T[] doComputeDerivatives(T t, T[] y) {
final T[] yDot = MathArrays.buildArray(getField(), getDimension());
yDot[0] = y[1];
yDot[1] = y[0].negate();
return yDot;
}
@Override
public T[] computeTheoreticalState(T t) {
T sin = t.add(a).sin();
T cos = t.add(a).cos();
final T[] y = MathArrays.buildArray(getField(), getDimension());
y[0] = sin.abs();
y[1] = (sin.getReal() >= 0) ? cos : cos.negate();
return y;
}
private static class Bounce<T extends RealFieldElement implements FieldEventHandler {
private int sign;
public Bounce() {
sign = +1;
}
public void init(FieldODEStateAndDerivative<T> state0, T t) {
}
public T g(FieldODEStateAndDerivative<T> state) {
return state.getState()[0].multiply(sign);
}
public Action eventOccurred(FieldODEStateAndDerivative<T> state, boolean increasing) {
// this sign change is needed because the state will be reset soon
sign = -sign;
return Action.RESET_STATE;
}
public FieldODEState<T> resetState(FieldODEStateAndDerivative state) {
T[] y = state.getState();
y[0] = y[0].negate();
y[1] = y[1].negate();
return new FieldODEState<T>(state.getTime(), y);
}
}
private static class Stop<T extends RealFieldElement implements FieldEventHandler {
public Stop() {
}
public void init(FieldODEStateAndDerivative<T> state0, T t) {
}
public T g(FieldODEStateAndDerivative<T> state) {
return state.getTime().subtract(12.0);
}
public Action eventOccurred(FieldODEStateAndDerivative<T> state, boolean increasing) {
return Action.STOP;
}
public FieldODEState<T> resetState(FieldODEStateAndDerivative state) {
return state;
}
}
}
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