parabolic_collision.cpp

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/*************************************************************************
 * Copyright (C) 2011 by Saleh Dindar and the Swarm-NG Development Team  *
 *                                                                       *
 * 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 3 of the License.        *
 *                                                                       *
 * This program is distributed in the hope t`hat 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.,                                       *
 * 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ************************************************************************/

#include "swarm/swarm.h"
#include <iostream>
using namespace swarm;
using namespace std;

const int nbod = 3;
const int nsys = 64;

const double mass_planet = 0.0001;

const double xpos[4] = {  -2.0, +2.0, -4.0, +4.0 };


const double mu = 1; 

const double R = 1; 

double norm(double x,double y){
        return sqrt(x*x+y*y);
}



int main(int argc, char* argv[]){
        if(argc <= 1){
                cout << "Usage: parabolic_collision <outputfilename>" << endl;
        }
        const string outputfn = argv[1];
        init(config());
        defaultEnsemble ens = defaultEnsemble::create(nbod,nsys);
        
        for(int i = 0; i < nsys ; i++){
                ensemble::SystemRef s = ens[i];
                s.id() = 0;
                s.time() = 0;
                s.set_active();
                
                // Stationary star at origin
                s[0].mass() = 1;
                s[0][0].pos() = 0, s[0][1].pos() = 0, s[0][2].pos() = 0 ;
                s[0][0].vel() = 0, s[0][1].vel() = 0, s[0][2].vel() = 0 ;
                
                
                // Planets on the parabola
                for(int b = 1; b < nbod; b++){
                        s[b].mass() = mass_planet;
                        
                        double x = xpos[b-1], y = x*x/4/R - R ;
                        double vmag = sqrt(2*mu/norm(x,y)) ;
                        double vdirx = (x/abs(x))/norm(1,x/2/R), vdiry = abs(x)/2/R / norm(1,x/2/R);
                        
                        
                        s[b][0].pos() = x  ,  s[b][0].vel() = -vmag*vdirx ;
                        s[b][1].pos() = y  ,  s[b][1].vel() = -vmag*vdiry ;
                        s[b][2].pos() = 0  ,  s[b][2].vel() = 0           ;
                }
                

        }
        snapshot::save_text(ens,outputfn);
}