
Java example source code file (FieldExpandableODE.java)
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The FieldExpandableODE.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/LICENSE2.0
*
* 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.util.ArrayList;
import java.util.List;
import org.apache.commons.math3.RealFieldElement;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MaxCountExceededException;
import org.apache.commons.math3.util.MathArrays;
/**
* This class represents a combined set of first order differential equations,
* with at least a primary set of equations expandable by some sets of secondary
* equations.
* <p>
* One typical use case is the computation of the Jacobian matrix for some ODE.
* In this case, the primary set of equations corresponds to the raw ODE, and we
* add to this set another bunch of secondary equations which represent the Jacobian
* matrix of the primary set.
* </p>
* <p>
* We want the integrator to use <em>only the primary set to estimate the
* errors and hence the step sizes. It should <em>not use the secondary
* equations in this computation. The {@link FirstOrderFieldIntegrator integrator} will
* be able to know where the primary set ends and so where the secondary sets begin.
* </p>
*
* @see FirstOrderFieldDifferentialEquations
* @see FieldSecondaryEquations
*
* @param <T> the type of the field elements
* @since 3.6
*/
public class FieldExpandableODE<T extends RealFieldElement {
/** Primary differential equation. */
private final FirstOrderFieldDifferentialEquations<T> primary;
/** Components of the expandable ODE. */
private List<FieldSecondaryEquations components;
/** Mapper for all equations. */
private FieldEquationsMapper<T> mapper;
/** Build an expandable set from its primary ODE set.
* @param primary the primary set of differential equations to be integrated.
*/
public FieldExpandableODE(final FirstOrderFieldDifferentialEquations<T> primary) {
this.primary = primary;
this.components = new ArrayList<FieldSecondaryEquations();
this.mapper = new FieldEquationsMapper<T>(null, primary.getDimension());
}
/** Get the mapper for the set of equations.
* @return mapper for the set of equations
*/
public FieldEquationsMapper<T> getMapper() {
return mapper;
}
/** Add a set of secondary equations to be integrated along with the primary set.
* @param secondary secondary equations set
* @return index of the secondary equation in the expanded state, to be used
* as the parameter to {@link FieldODEState#getSecondaryState(int)} and
* {@link FieldODEStateAndDerivative#getSecondaryDerivative(int)} (beware index
* 0 corresponds to main state, additional states start at 1)
*/
public int addSecondaryEquations(final FieldSecondaryEquations<T> secondary) {
components.add(secondary);
mapper = new FieldEquationsMapper<T>(mapper, secondary.getDimension());
return components.size();
}
/** Initialize equations at the start of an ODE integration.
* @param t0 value of the independent <I>time variable at integration start
* @param y0 array containing the value of the state vector at integration start
* @param finalTime target time for the integration
* @exception MaxCountExceededException if the number of functions evaluations is exceeded
* @exception DimensionMismatchException if arrays dimensions do not match equations settings
*/
public void init(final T t0, final T[] y0, final T finalTime) {
// initialize primary equations
int index = 0;
final T[] primary0 = mapper.extractEquationData(index, y0);
primary.init(t0, primary0, finalTime);
// initialize secondary equations
while (++index < mapper.getNumberOfEquations()) {
final T[] secondary0 = mapper.extractEquationData(index, y0);
components.get(index  1).init(t0, primary0, secondary0, finalTime);
}
}
/** Get the current time derivative of the complete state vector.
* @param t current value of the independent <I>time variable
* @param y array containing the current value of the complete state vector
* @return time derivative of the complete state vector
* @exception MaxCountExceededException if the number of functions evaluations is exceeded
* @exception DimensionMismatchException if arrays dimensions do not match equations settings
*/
public T[] computeDerivatives(final T t, final T[] y)
throws MaxCountExceededException, DimensionMismatchException {
final T[] yDot = MathArrays.buildArray(t.getField(), mapper.getTotalDimension());
// compute derivatives of the primary equations
int index = 0;
final T[] primaryState = mapper.extractEquationData(index, y);
final T[] primaryStateDot = primary.computeDerivatives(t, primaryState);
mapper.insertEquationData(index, primaryStateDot, yDot);
// Add contribution for secondary equations
while (++index < mapper.getNumberOfEquations()) {
final T[] componentState = mapper.extractEquationData(index, y);
final T[] componentStateDot = components.get(index  1).computeDerivatives(t, primaryState, primaryStateDot,
componentState);
mapper.insertEquationData(index, componentStateDot, yDot);
}
return yDot;
}
}
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