RungeKutta2IvpOdeSolver.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 
00030 #include "RungeKutta2IvpOdeSolver.hpp"
00031 
00032 void RungeKutta2IvpOdeSolver::CalculateNextYValue(AbstractOdeSystem* pAbstractOdeSystem,
00033                                                   double timeStep,
00034                                                   double time,
00035                                                   std::vector<double>& rCurrentYValues,
00036                                                   std::vector<double>& rNextYValues)
00037 {
00038     /*
00039      * Apply Runge-Kutta 2nd order method for each timestep in AbstractOneStepIvpSolver.
00040      * Calculates a vector containing the next Y value from the current one for each
00041      * equation in the system.
00042      */
00043 
00044     const unsigned num_equations = pAbstractOdeSystem->GetNumberOfStateVariables();
00045 
00046     std::vector<double> k1(num_equations);
00047     std::vector<double>& dy = rNextYValues; // re-use memory
00048 
00049     // Work out k1
00050     pAbstractOdeSystem->EvaluateYDerivatives(time, rCurrentYValues, dy);
00051 
00052     for (unsigned i=0; i<num_equations; i++)
00053     {
00054         k1[i] = timeStep*dy[i];
00055         k1[i] = k1[i]/2.0 + rCurrentYValues[i];
00056     }
00057 
00058     // Work out k2 and new solution
00059     pAbstractOdeSystem->EvaluateYDerivatives(time+timeStep/2.0, k1, dy);
00060     for (unsigned i=0; i<num_equations; i++)
00061     {
00062         rNextYValues[i] = rCurrentYValues[i] + timeStep*dy[i];
00063     }
00064 }

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