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c:/home/kevn/src/animaniac/ani/Dynamics/solvers/HeunODEsolver.h

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00001 
00003 //
00004 //               -=     ODE solver using Heun's Method     =-
00005 //
00006 // Definition: "a 2nd order ordinary differential equation solver"
00007 //
00009 //
00010 //    $RCSfile: HeunODEsolver.h,v $
00011 //    $Date: 2002/01/10 03:10:47 $
00012 //    $Revision: 1.4 $
00013 //    Copyright (C) 1998, 1999, 2000  Kevin Meinert, kevin@vrsource.org
00014 //
00015 //    This library is free software; you can redistribute it and/or
00016 //    modify it under the terms of the GNU Library General Public
00017 //    License as published by the Free Software Foundation; either
00018 //    version 2 of the License, or (at your option) any later version.
00019 //
00020 //    This library is distributed in the hope that it will be useful,
00021 //    but WITHOUT ANY WARRANTY; without even the implied warranty of
00022 //    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00023 //    Library General Public License for more details.
00024 //
00025 //    You should have received a copy of the GNU Library General Public
00026 //    License along with this library; if not, write to the Free
00027 //    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
00028 //
00030 #ifndef SECONDORDER_RUNGEKUTTA_METHOD
00031 #define SECONDORDER_RUNGEKUTTA_METHOD
00032 
00033 #include "ani/Dynamics/ODEsolver.h"
00034 
00035 namespace ani
00036 {
00037 
00038    //: the second-order Runge-Kutta method 
00039    template <class _item>
00040    class HeunODEsolver : public ODEsolver<_item>
00041    {
00042    public:
00043       HeunODEsolver() {}
00044       virtual ~HeunODEsolver() {}
00045 
00046       //: the second-order Runge-Kutta method 
00047       //
00048       // give:
00049       //  currentState = current state of the item
00050       //  currentTime = current time of the item
00051       //  timeDelta = current stepsize (t(n) - t(n+1)) == time delta
00052       // returns:
00053       //  currentState = x(t0 + h) == the next state of the item after taking this step...
00054       virtual void exec( _item& currentState, float timeDelta )
00055       {      
00056          // compute next state.
00057          
00058          // any particle that is put into f() needs to have its mass and force accums set
00059          // to equal the current _item, since all the operations only act on the phase space
00060          // (pos, vel), this is needed.
00061          temp.copy( currentState );
00062 
00063          // k1 = h * func( x0, t0 );
00064          //     f = func(..., ...)
00065          f.computeDerivative( currentState, timeDelta * 0.0f );
00066          //     k1 = h * f
00067          k1.multiplyPhase( f, timeDelta );
00068 
00069          //: k2 = h * func( x0 + k1, t0 + h );
00070          //     f = func(..., ...)
00071          temp.addPhase( currentState, k1 );
00072          f.computeDerivative( temp, timeDelta * 1.0f );
00073          //     k4 = h * f
00074          k2.multiplyPhase( f, timeDelta );
00075 
00076          // xt0h = x0  +  1/2 * (k1  +  k2);
00077          //currentState = currentState + 1/2 * (k1 + k2);
00078          changeInState.addPhase( k1, k2 );
00079          changeInState.multiplyPhase( 0.5f );
00080 
00081          currentState.addPhase( changeInState );
00082          currentState.normalize();
00083       }
00084 
00085       // create the two gradient or ``k'' terms
00086       _item k1, k2;
00087       _item changeInState, f, temp;
00088    };
00089 };
00090 
00091 #endif

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