/*
* OpenPixi - Open Particle-In-Cell (PIC) Simulator
* Copyright (C) 2012 OpenPixi.org
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
package org.openpixi.pixi.physics.solver.relativistic;
import org.openpixi.pixi.physics.*;
import org.openpixi.pixi.physics.force.Force;
import org.openpixi.pixi.physics.particles.Particle;
import org.openpixi.pixi.physics.solver.Solver;
/**This class represents the LeapFrog algorithm and the equations that are used one can be find here:
* http://phycomp.technion.ac.il/~david/thesis/node34.html
* and also here:
* http://www.artcompsci.org/vol_1/v1_web/node34.html#leapfrog-step2
*/
public class LeapFrogRelativistic implements Solver{
RelativisticVelocity relvelocity;
public LeapFrogRelativistic(double c)
{
relvelocity = new RelativisticVelocity(c);
}
/**
* LeapFrog algorithm. The damping is implemented with an linear error O(dt).
* Warning: the velocity is stored half a time step ahead of the position.
* @param p before the update: x(t), u(t+dt/2), a(t);
* after the update: x(t+dt), u(t+3*dt/2), a(t+dt)
* u(t) is the relativistic momentum
*/
public void step(Particle p, Force f, double dt) {
double gamma = relvelocity.calculateGamma(p);
// x(t+dt) = x(t) + c(t+dt/2) * dt / gamma
p.setX(p.getX() + p.getVx() * dt / gamma);
p.setY(p.getY() + p.getVy() * dt / gamma);
// a(t+dt) = F(u(t+dt/2), x(t+dt)) / m
// WARNING: Force is evaluated at two different times t+dt/2 and t+dt!
p.setAx(f.getForceX(p) / p.getMass());
p.setAy(f.getForceY(p) / p.getMass());
// u(t+3*dt/2) = u(t+dt/2) + a(t+dt)*dt
p.setVx(p.getVx() + p.getAx() * dt);
p.setVy(p.getVy() + p.getAy() * dt);
}
/**
* prepare method for bringing the velocity in the desired half step
* @param p before the update: v(t);
* after the update: v(t+dt/2)
*/
public void prepare(Particle p, Force f, double dt)
{
//a(t) = F(v(t), x(t)) / m
p.setAx(f.getForceX(p) / p.getMass());
p.setAy(f.getForceY(p) / p.getMass());
//v(t + dt / 2) = v(t) + a(t)*dt / 2
p.setVx(p.getVx() + p.getAx() * dt);
p.setVy(p.getVy() + p.getAy() * dt);
}
/**
* complete method for bringing the velocity in the desired half step
* @param p before the update: v(t+dt/2);
* after the update: v(t)
*/
public void complete(Particle p, Force f, double dt)
{
//v(t) = v(t + dt / 2) - a(t)*dt / 2
p.setVx(p.getVx() - p.getAx() * dt);
p.setVy(p.getVy() - p.getAy() * dt);
}
}