1dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond/* 2dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Licensed to the Apache Software Foundation (ASF) under one or more 3dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * contributor license agreements. See the NOTICE file distributed with 4dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * this work for additional information regarding copyright ownership. 5dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * The ASF licenses this file to You under the Apache License, Version 2.0 6dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * (the "License"); you may not use this file except in compliance with 7dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * the License. You may obtain a copy of the License at 8dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 9dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * http://www.apache.org/licenses/LICENSE-2.0 10dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 11dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Unless required by applicable law or agreed to in writing, software 12dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * distributed under the License is distributed on an "AS IS" BASIS, 13dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * See the License for the specific language governing permissions and 15dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * limitations under the License. 16dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 17dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 18dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondpackage org.apache.commons.math.ode; 19dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 20dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondimport org.apache.commons.math.ode.DerivativeException; 21dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 22dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond/** This class converts second order differential equations to first 23dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * order ones. 24dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 25dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * <p>This class is a wrapper around a {@link 26dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * SecondOrderDifferentialEquations} which allow to use a {@link 27dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * FirstOrderIntegrator} to integrate it.</p> 28dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 29dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * <p>The transformation is done by changing the n dimension state 30dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * vector to a 2n dimension vector, where the first n components are 31dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * the initial state variables and the n last components are their 32dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * first time derivative. The first time derivative of this state 33dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * vector then really contains both the first and second time 34dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * derivative of the initial state vector, which can be handled by the 35dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * underlying second order equations set.</p> 36dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 37dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * <p>One should be aware that the data is duplicated during the 38dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * transformation process and that for each call to {@link 39dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * #computeDerivatives computeDerivatives}, this wrapper does copy 4n 40dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * scalars : 2n before the call to {@link 41dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * SecondOrderDifferentialEquations#computeSecondDerivatives 42dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * computeSecondDerivatives} in order to dispatch the y state vector 43dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * into z and zDot, and 2n after the call to gather zDot and zDDot 44dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * into yDot. Since the underlying problem by itself perhaps also 45dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * needs to copy data and dispatch the arrays into domain objects, 46dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * this has an impact on both memory and CPU usage. The only way to 47dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * avoid this duplication is to perform the transformation at the 48dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * problem level, i.e. to implement the problem as a first order one 49dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * and then avoid using this class.</p> 50dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 51dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @see FirstOrderIntegrator 52dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @see FirstOrderDifferentialEquations 53dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @see SecondOrderDifferentialEquations 54dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @version $Revision: 1073158 $ $Date: 2011-02-21 22:46:52 +0100 (lun. 21 févr. 2011) $ 55dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @since 1.2 56dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 57dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 58dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondpublic class FirstOrderConverter implements FirstOrderDifferentialEquations { 59dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 60dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** Underlying second order equations set. */ 61dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private final SecondOrderDifferentialEquations equations; 62dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 63dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** second order problem dimension. */ 64dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private final int dimension; 65dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 66dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** state vector. */ 67dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private final double[] z; 68dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 69dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** first time derivative of the state vector. */ 70dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private final double[] zDot; 71dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 72dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** second time derivative of the state vector. */ 73dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private final double[] zDDot; 74dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 75dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** Simple constructor. 76dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Build a converter around a second order equations set. 77dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param equations second order equations set to convert 78dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 79dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public FirstOrderConverter (final SecondOrderDifferentialEquations equations) { 80dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond this.equations = equations; 81dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond dimension = equations.getDimension(); 82dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond z = new double[dimension]; 83dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond zDot = new double[dimension]; 84dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond zDDot = new double[dimension]; 85dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 86dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 87dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** Get the dimension of the problem. 88dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * <p>The dimension of the first order problem is twice the 89dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * dimension of the underlying second order problem.</p> 90dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @return dimension of the problem 91dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 92dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public int getDimension() { 93dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond return 2 * dimension; 94dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 95dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 96dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** Get the current time derivative of the state vector. 97dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param t current value of the independent <I>time</I> variable 98dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param y array containing the current value of the state vector 99dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param yDot placeholder array where to put the time derivative of the state vector 100dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @throws DerivativeException this exception is propagated to the caller if the 101dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * underlying user function triggers one 102dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 103dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public void computeDerivatives(final double t, final double[] y, final double[] yDot) 104dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond throws DerivativeException { 105dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 106dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // split the state vector in two 107dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond System.arraycopy(y, 0, z, 0, dimension); 108dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond System.arraycopy(y, dimension, zDot, 0, dimension); 109dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 110dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // apply the underlying equations set 111dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond equations.computeSecondDerivatives(t, z, zDot, zDDot); 112dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 113dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // build the result state derivative 114dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond System.arraycopy(zDot, 0, yDot, 0, dimension); 115dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond System.arraycopy(zDDot, 0, yDot, dimension, dimension); 116dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 117dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 118dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 119dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond} 120