Paste: java nbody

/* The Great Computer Language Shootout
   http://shootout.alioth.debian.org/

   contributed by Mark C. Lewis
*/

import java.text.*;

public final class nbody {
	public static void main(String[] args) {
	   NumberFormat nf = NumberFormat.getInstance();
	   nf.setMaximumFractionDigits(9);
	   nf.setMinimumFractionDigits(9);
	   nf.setGroupingUsed(false);

	   int n = 1000000;

	  for(int xx = 0; xx < 8; xx++)
		{
			System.out.println("Run #" + xx);
			long start = System.currentTimeMillis();
			NBodySystem bodies = new NBodySystem();

		System.out.println(nf.format(bodies.energy()) );
		for (int i=0; i<n; ++i) {
		   bodies.advance(0.01);
		}
		System.out.println(nf.format(bodies.energy()) );
			long end = System.currentTimeMillis();
			System.out.println("Time: " + (end - start));
		}
		
	}
}


final class NBodySystem {
	private Body[] bodies;

	public NBodySystem(){
		bodies = new Body[]{
		      Body.sun(),
		      Body.jupiter(),
		      Body.saturn(),
		      Body.uranus(),
		      Body.neptune()
		   };

		double px = 0.0;
		double py = 0.0;
		double pz = 0.0;
		for(int i=0; i < bodies.length; ++i) {
			px += bodies[i].vx * bodies[i].mass;
			py += bodies[i].vy * bodies[i].mass;
			pz += bodies[i].vz * bodies[i].mass;
		}
		bodies[0].offsetMomentum(px,py,pz);
	}

	public void advance(double dt) {
	   double dx, dy, dz, distance, mag;

		for(int i=0; i < bodies.length; ++i) {
			for(int j=i+1; j < bodies.length; ++j) {
				dx = bodies[i].x - bodies[j].x;
				dy = bodies[i].y - bodies[j].y;
				dz = bodies[i].z - bodies[j].z;

				distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
				mag = dt / (distance * distance * distance);

				bodies[i].vx -= dx * bodies[j].mass * mag;
				bodies[i].vy -= dy * bodies[j].mass * mag;
				bodies[i].vz -= dz * bodies[j].mass * mag;

				bodies[j].vx += dx * bodies[i].mass * mag;
				bodies[j].vy += dy * bodies[i].mass * mag;
				bodies[j].vz += dz * bodies[i].mass * mag;
			}
		}

		for(int i=0; i < bodies.length; ++i) {
			bodies[i].x += dt * bodies[i].vx;
			bodies[i].y += dt * bodies[i].vy;
			bodies[i].z += dt * bodies[i].vz;
		}
	}

	public double energy(){
		double dx, dy, dz, distance;
		double e = 0.0;

		for (int i=0; i < bodies.length; ++i) {
			e += 0.5 * bodies[i].mass *
			   ( bodies[i].vx * bodies[i].vx
			   + bodies[i].vy * bodies[i].vy
			   + bodies[i].vz * bodies[i].vz );

			for (int j=i+1; j < bodies.length; ++j) {
				dx = bodies[i].x - bodies[j].x;
				dy = bodies[i].y - bodies[j].y;
				dz = bodies[i].z - bodies[j].z;

				distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
				e -= (bodies[i].mass * bodies[j].mass) / distance;
			}
		}
		return e;
	}
}


final class Body {
   static final double PI = 3.141592653589793;
   static final double SOLAR_MASS = 4 * PI * PI;
	static final double DAYS_PER_YEAR = 365.24;

	public double x, y, z, vx, vy, vz, mass;

	public Body(){}

	static Body jupiter(){
	   Body p = new Body();
	   p.x = 4.84143144246472090e+00;
	   p.y = -1.16032004402742839e+00;
	   p.z = -1.03622044471123109e-01;
	   p.vx = 1.66007664274403694e-03 * DAYS_PER_YEAR;
	   p.vy = 7.69901118419740425e-03 * DAYS_PER_YEAR;
	   p.vz = -6.90460016972063023e-05 * DAYS_PER_YEAR;
	   p.mass = 9.54791938424326609e-04 * SOLAR_MASS;
	   return p;
	}

	static Body saturn(){
	   Body p = new Body();
	   p.x = 8.34336671824457987e+00;
	   p.y = 4.12479856412430479e+00;
	   p.z = -4.03523417114321381e-01;
	   p.vx = -2.76742510726862411e-03 * DAYS_PER_YEAR;
	   p.vy = 4.99852801234917238e-03 * DAYS_PER_YEAR;
	   p.vz = 2.30417297573763929e-05 * DAYS_PER_YEAR;
	   p.mass = 2.85885980666130812e-04 * SOLAR_MASS;
	   return p;
	}

	static Body uranus(){
	   Body p = new Body();
	   p.x = 1.28943695621391310e+01;
	   p.y = -1.51111514016986312e+01;
	   p.z = -2.23307578892655734e-01;
	   p.vx = 2.96460137564761618e-03 * DAYS_PER_YEAR;
	   p.vy = 2.37847173959480950e-03 * DAYS_PER_YEAR;
	   p.vz = -2.96589568540237556e-05 * DAYS_PER_YEAR;
	   p.mass = 4.36624404335156298e-05 * SOLAR_MASS;
	   return p;
	}

	static Body neptune(){
	   Body p = new Body();
	   p.x = 1.53796971148509165e+01;
	   p.y = -2.59193146099879641e+01;
	   p.z = 1.79258772950371181e-01;
	   p.vx = 2.68067772490389322e-03 * DAYS_PER_YEAR;
	   p.vy = 1.62824170038242295e-03 * DAYS_PER_YEAR;
	   p.vz = -9.51592254519715870e-05 * DAYS_PER_YEAR;
	   p.mass = 5.15138902046611451e-05 * SOLAR_MASS;
	   return p;
	}

	static Body sun(){
	   Body p = new Body();
	   p.mass = SOLAR_MASS;
	   return p;
	}

	Body offsetMomentum(double px, double py, double pz){
	   vx = -px / SOLAR_MASS;
	   vy = -py / SOLAR_MASS;
	   vz = -pz / SOLAR_MASS;
	   return this;
	}
}