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git-svn-id: https://reactphysics3d.googlecode.com/svn/trunk@200 92aac97c-a6ce-11dd-a772-7fcde58d38e6

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chappuis.daniel 2009-10-08 21:40:08 +00:00
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91
sources/reactphysics3d/engine/RK4.cpp
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/****************************************************************************
* Copyright (C) 2009 Daniel Chappuis *
****************************************************************************
* This file is part of ReactPhysics3D. *
* *
* ReactPhysics3D is free software: you can redistribute it and/or modify *
* it under the terms of the GNU Lesser General Public License as published *
* by the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* ReactPhysics3D is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public License *
* along with ReactPhysics3D. If not, see <http://www.gnu.org/licenses/>. *
***************************************************************************/
// Libraries
#include "RK4.h"
#include <cassert>
// We want to use the ReactPhysics3D namespace
using namespace reactphysics3d;
// Constructor
RK4::RK4() {
}
// Copy-constructor
RK4::RK4(const RK4& rk4) {
}
// Destructor
RK4::~RK4() {
}
// Compute a derivative body state at time t
DerivativeBodyState RK4::evaluate(const BodyState& bodyState, const Time& time) {
// Compute the derivaties values at time t
Vector3D linearVelocity = bodyState.getLinearVelocity();
Vector3D force = bodyState.computeForce(time);
Vector3D torque = bodyState.computeTorque(time);
Quaternion spin = bodyState.getSpin();
// Return the derivative body state at time t
return DerivativeBodyState(linearVelocity, force, torque, spin);
}
// Compute a derivative body state at time t + dt according to the last derivative body state
DerivativeBodyState RK4::evaluate(BodyState bodyState, const Time& time, const Time& timeStep,
const DerivativeBodyState& lastDerivativeBodyState) {
// Compute the bodyState at time t + dt
bodyState.computeAtTime(timeStep, lastDerivativeBodyState);
// Compute the derivaties values at time t
Vector3D linearVelocity = bodyState.getLinearVelocity();
Vector3D force = bodyState.computeForce(time + timeStep);
Vector3D torque = bodyState.computeTorque(time + timeStep);
Quaternion spin = bodyState.getSpin();
// Return the derivative body state at time t
return DerivativeBodyState(linearVelocity, force, torque, spin);
}
// Integrate a body state over time. This method use the RK4 integration algorithm
void RK4::integrate(BodyState& bodyState, const Time& time, const Time& timeStep) {
// Compute the 4 derivatives body states at different time values.
DerivativeBodyState a = evaluate(bodyState, time);
DerivativeBodyState b = evaluate(bodyState, time, timeStep*0.5, a);
DerivativeBodyState c = evaluate(bodyState, time, timeStep*0.5, b);
DerivativeBodyState d = evaluate(bodyState, time, timeStep, c);
double dt = timeStep.getValue(); // Timestep
// Compute the integrated body state
bodyState.setPosition(bodyState.getPosition() + (a.getLinearVelocity() + (b.getLinearVelocity() + c.getLinearVelocity()) * 2.0 +
d.getLinearVelocity()) * (1.0/6.0) * dt);
bodyState.setLinearMomentum(bodyState.getLinearMomentum() + (a.getForce() + (b.getForce() + c.getForce())*2.0 + d.getForce()) * (1.0/6.0) * dt);
bodyState.setOrientation(bodyState.getOrientation() + (a.getSpin() + (b.getSpin() + c.getSpin())*2.0 + d.getSpin()) * (1.0/6.0) * dt);
bodyState.setAngularMomentum(bodyState.getAngularMomentum() + (a.getTorque() + (b.getTorque() + c.getTorque())*2.0 + d.getTorque()) * (1.0/6.0) * dt);
// Recalculate the secondary values of the body state
bodyState.recalculate();
}

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sources/reactphysics3d/engine/RK4.h
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/****************************************************************************
* Copyright (C) 2009 Daniel Chappuis *
****************************************************************************
* This file is part of ReactPhysics3D. *
* *
* ReactPhysics3D is free software: you can redistribute it and/or modify *
* it under the terms of the GNU Lesser General Public License as published *
* by the Free Software Foundation, either version 3 of the License, or *
* (at your option) any later version. *
* *
* ReactPhysics3D is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
* GNU Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public License *
* along with ReactPhysics3D. If not, see <http://www.gnu.org/licenses/>. *
***************************************************************************/
#ifndef RK4_H
#define RK4_H
// Libraries
#include "IntegrationAlgorithm.h"
#include "../body/BodyState.h"
#include "../body/DerivativeBodyState.h"
// Namespace ReactPhysics3D
namespace reactphysics3d {
/* -------------------------------------------------------------------
Class RK4 :
This class will be used to solve the differential equation of
movement by integrating a body state. This class implements
the Runge-Kutta 4 (RK4) integrator.
-------------------------------------------------------------------
*/
class RK4 : public IntegrationAlgorithm {
private :
DerivativeBodyState evaluate(const BodyState& bodyState, const Time& time); // Compute a derivative body state
DerivativeBodyState evaluate(BodyState bodyState, const Time& time,
const Time& timeStep, const DerivativeBodyState& lastDerivativeBodyState); // Compute a derivative body state
public :
RK4(); // Constructor
RK4(const RK4& rk4); // Copy-constructor
virtual ~RK4(); // Destructor
void integrate(BodyState& bodyState, const Time& t, const Time& dt); // Integrate a body state over time
};
}
#endif