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/*=========================================================================
Program: Visualization Toolkit
Module: $RCSfile: vtkRungeKutta2.cxx,v $
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notice for more information.
=========================================================================*/
#include "vtkRungeKutta2.h"
#include "vtkFunctionSet.h"
#include "vtkObjectFactory.h"
vtkCxxRevisionMacro(vtkRungeKutta2, "$Revision: 1.14 $");
vtkStandardNewMacro(vtkRungeKutta2);
vtkRungeKutta2::vtkRungeKutta2()
{
}
vtkRungeKutta2::~vtkRungeKutta2()
{
}
// Calculate next time step
int vtkRungeKutta2::ComputeNextStep(double* xprev, double* dxprev, double* xnext,
double t, double& delT, double& delTActual,
double, double, double, double& error)
{
int i, numDerivs, numVals;
delTActual = delT;
error = 0.0;
if (!this->FunctionSet)
{
vtkErrorMacro("No derivative functions are provided!");
return NOT_INITIALIZED;
}
if (!this->Initialized)
{
vtkErrorMacro("Integrator not initialized!");
return NOT_INITIALIZED;
}
numDerivs = this->FunctionSet->GetNumberOfFunctions();
numVals = numDerivs + 1;
for(i=0; i<numVals-1; i++)
{
this->Vals[i] = xprev[i];
}
this->Vals[numVals-1] = t;
// Obtain the derivatives dx_i at x_i
if (dxprev)
{
for(i=0; i<numDerivs; i++)
{
this->Derivs[i] = dxprev[i];
}
}
else if ( !this->FunctionSet->FunctionValues(this->Vals, this->Derivs) )
{
memcpy(xnext, this->Vals, (numVals-1)*sizeof(double));
return OUT_OF_DOMAIN;
}
// Half-step
for(i=0; i<numVals-1; i++)
{
this->Vals[i] = xprev[i] + delT/2.0*this->Derivs[i];
}
this->Vals[numVals-1] = t + delT/2.0;
// Obtain the derivatives at x_i + dt/2 * dx_i
if (!this->FunctionSet->FunctionValues(this->Vals, this->Derivs))
{
memcpy(xnext, this->Vals, (numVals-1)*sizeof(double));
return OUT_OF_DOMAIN;
}
// Calculate x_i using improved values of derivatives
for(i=0; i<numDerivs; i++)
{
xnext[i] = xprev[i] + delT*this->Derivs[i];
}
return 0;
}
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