RungeKutta4IvpOdeSolver.cpp

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*/
 
#include "RungeKutta4IvpOdeSolver.hpp"
 
void RungeKutta4IvpOdeSolver::CalculateNextYValue(AbstractOdeSystem* pAbstractOdeSystem,
                                                  double timeStep,
                                                  double time,
                                                  std::vector<double>& rCurrentYValues,
                                                  std::vector<double>& rNextYValues)
{
    /*
     * Apply Runge-Kutta 4th order method for each timestep in AbstractOneStepIvpSolver.
     * Calculates a vector containing the next Y value from the current one for each
     * equation in the system.
     */
 
    const unsigned num_equations = pAbstractOdeSystem->GetNumberOfStateVariables();
 
    if (num_equations != k1.size())
    {
        k1.resize(num_equations);
        k2.resize(num_equations);
        k3.resize(num_equations);
        k4.resize(num_equations);
        yki.resize(num_equations);
    }
 
    std::vector<double>& dy = rNextYValues; // re-use memory
 
    pAbstractOdeSystem->EvaluateYDerivatives(time, rCurrentYValues, dy);
    for (unsigned i=0; i<num_equations; i++)
    {
        k1[i] = timeStep*dy[i];
        yki[i] = rCurrentYValues[i] + 0.5*k1[i];
    }
 
    pAbstractOdeSystem->EvaluateYDerivatives(time+0.5*timeStep, yki, dy);
    for (unsigned i=0; i<num_equations; i++)
    {
        k2[i] = timeStep*dy[i];
        yki[i] = rCurrentYValues[i] + 0.5*k2[i];
    }
 
    pAbstractOdeSystem->EvaluateYDerivatives(time+0.5*timeStep, yki, dy);
    for (unsigned i=0; i<num_equations; i++)
    {
        k3[i] = timeStep*dy[i];
        yki[i] = rCurrentYValues[i] + k3[i];
    }
 
    pAbstractOdeSystem->EvaluateYDerivatives(time+timeStep, yki, dy);
    for (unsigned i=0; i<num_equations; i++)
    {
        k4[i] = timeStep*dy[i];
        rNextYValues[i] = rCurrentYValues[i] + (k1[i]+2*k2[i]+2*k3[i]+k4[i])/6.0;
    }
}
 
 
// Serialization for Boost >= 1.36
#include "SerializationExportWrapperForCpp.hpp"
CHASTE_CLASS_EXPORT(RungeKutta4IvpOdeSolver)