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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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package org.apache.commons.math.ode;
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/** This class converts second order differential equations to first
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* <p>This class is a wrapper around a {@link
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* SecondOrderDifferentialEquations} which allow to use a {@link
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* FirstOrderIntegrator} to integrate it.</p>
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* <p>The transformation is done by changing the n dimension state
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* vector to a 2n dimension vector, where the first n components are
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* the initial state variables and the n last components are their
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* first time derivative. The first time derivative of this state
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* vector then really contains both the first and second time
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* derivative of the initial state vector, which can be handled by the
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* underlying second order equations set.</p>
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* <p>One should be aware that the data is duplicated during the
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* transformation process and that for each call to {@link
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* #computeDerivatives computeDerivatives}, this wrapper does copy 4n
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* scalars : 2n before the call to {@link
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* SecondOrderDifferentialEquations#computeSecondDerivatives
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* computeSecondDerivatives} in order to dispatch the y state vector
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* into z and zDot, and 2n after the call to gather zDot and zDDot
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* into yDot. Since the underlying problem by itself perhaps also
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* needs to copy data and dispatch the arrays into domain objects,
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* this has an impact on both memory and CPU usage. The only way to
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* avoid this duplication is to perform the transformation at the
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* problem level, i.e. to implement the problem as a first order one
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* and then avoid using this class.</p>
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* @see FirstOrderIntegrator
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* @see FirstOrderDifferentialEquations
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* @see SecondOrderDifferentialEquations
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* @version $Revision: 620312 $ $Date: 2008-02-10 12:28:59 -0700 (Sun, 10 Feb 2008) $
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public class FirstOrderConverter
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implements FirstOrderDifferentialEquations {
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/** Simple constructor.
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* Build a converter around a second order equations set.
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* @param equations second order equations set to convert
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public FirstOrderConverter (SecondOrderDifferentialEquations equations) {
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this.equations = equations;
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dimension = equations.getDimension();
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z = new double[dimension];
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zDot = new double[dimension];
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zDDot = new double[dimension];
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/** Get the dimension of the problem.
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* <p>The dimension of the first order problem is twice the
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* dimension of the underlying second order problem.</p>
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* @return dimension of the problem
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public int getDimension() {
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/** Get the current time derivative of the state vector.
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* @param t current value of the independent <I>time</I> variable
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* @param y array containing the current value of the state vector
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* @param yDot placeholder array where to put the time derivative of the state vector
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* @throws DerivativeException this exception is propagated to the caller if the
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* underlying user function triggers one
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public void computeDerivatives(double t, double[] y, double[] yDot)
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throws DerivativeException {
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// split the state vector in two
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System.arraycopy(y, 0, z, 0, dimension);
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System.arraycopy(y, dimension, zDot, 0, dimension);
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// apply the underlying equations set
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equations.computeSecondDerivatives(t, z, zDot, zDDot);
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// build the result state derivative
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System.arraycopy(zDot, 0, yDot, 0, dimension);
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System.arraycopy(zDDot, 0, yDot, dimension, dimension);
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/** Underlying second order equations set. */
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private SecondOrderDifferentialEquations equations;
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/** second order problem dimension. */
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private int dimension;
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/** first time derivative of the state vector. */
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private double[] zDot;
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/** second time derivative of the state vector. */
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private double[] zDDot;