RungeKutta4IvpOdeSolver.cpp

00001 /*
00002 
00003 Copyright (C) University of Oxford, 2005-2009
00004 
00005 University of Oxford means the Chancellor, Masters and Scholars of the
00006 University of Oxford, having an administrative office at Wellington
00007 Square, Oxford OX1 2JD, UK.
00008 
00009 This file is part of Chaste.
00010 
00011 Chaste is free software: you can redistribute it and/or modify it
00012 under the terms of the GNU Lesser General Public License as published
00013 by the Free Software Foundation, either version 2.1 of the License, or
00014 (at your option) any later version.
00015 
00016 Chaste is distributed in the hope that it will be useful, but WITHOUT
00017 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
00018 FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
00019 License for more details. The offer of Chaste under the terms of the
00020 License is subject to the License being interpreted in accordance with
00021 English Law and subject to any action against the University of Oxford
00022 being under the jurisdiction of the English Courts.
00023 
00024 You should have received a copy of the GNU Lesser General Public License
00025 along with Chaste. If not, see <http://www.gnu.org/licenses/>.
00026 
00027 */
00028 
00029 
00033 #include "RungeKutta4IvpOdeSolver.hpp"
00034 #include "AbstractIvpOdeSolver.hpp"
00035 #include "AbstractOdeSystem.hpp"
00036 #include "OdeSolution.hpp"
00037 
00038 //#include <iostream>
00039 #include <vector>
00040 
00041 
00054 void RungeKutta4IvpOdeSolver::CalculateNextYValue(AbstractOdeSystem* pAbstractOdeSystem,
00055                                                   double timeStep,
00056                                                   double time,
00057                                                   std::vector<double>& currentYValues,
00058                                                   std::vector<double>& nextYValues)
00059 {
00060     // Apply Runge-Kutta 4th Order method for each timestep in AbstractOneStepIvpSolver.
00061     // Calculates a vector containing the next Y value from the current one for each
00062     // equation in the system.
00063 
00064     const unsigned num_equations = pAbstractOdeSystem->GetNumberOfStateVariables();
00065 
00066     if (num_equations != k1.size())
00067     {
00068         k1.resize(num_equations);
00069         k2.resize(num_equations);
00070         k3.resize(num_equations);
00071         k4.resize(num_equations);
00072         yki.resize(num_equations);
00073     }
00074 
00075     std::vector<double>& dy = nextYValues; // re-use memory
00076 
00077     pAbstractOdeSystem->EvaluateYDerivatives(time, currentYValues, dy);
00078     for (unsigned i=0;i<num_equations; i++)
00079     {
00080         k1[i]=timeStep*dy[i];
00081         yki[i] = currentYValues[i] + 0.5*k1[i];
00082     }
00083 
00084     pAbstractOdeSystem->EvaluateYDerivatives(time+0.5*timeStep, yki, dy);
00085     for (unsigned i=0;i<num_equations; i++)
00086     {
00087         k2[i]=timeStep*dy[i];
00088         yki[i] = currentYValues[i] + 0.5*k2[i];
00089     }
00090 
00091     pAbstractOdeSystem->EvaluateYDerivatives(time+0.5*timeStep, yki, dy);
00092     for (unsigned i=0;i<num_equations; i++)
00093     {
00094         k3[i]=timeStep*dy[i];
00095         yki[i] = currentYValues[i] + k3[i];
00096     }
00097 
00098     pAbstractOdeSystem->EvaluateYDerivatives(time+timeStep, yki, dy);
00099     for (unsigned i=0;i<num_equations; i++)
00100     {
00101         k4[i]=timeStep*dy[i];
00102         nextYValues[i] = currentYValues[i] + (k1[i]+2*k2[i]+2*k3[i]+k4[i])/6.0;
00103     }
00104 }

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