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Java example source code file (FieldExpandableODE.java)

This example Java source code file (FieldExpandableODE.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arraylist, dimensionmismatchexception, fieldequationsmapper, fieldexpandableode, fieldsecondaryequations, firstorderfielddifferentialequations, maxcountexceededexception, realfieldelement, util

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/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.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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