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/* The Computer Language Shootout
http://shootout.alioth.debian.org/
contributed by Mark C. Lewis
*/
import java.text.*;
public final class nbody {
private static final NumberFormat nf = new DecimalFormat("#0.000000000");
public static void main(String[] args) {
int n = Integer.parseInt(args[0]);
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()) );
}
}
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;
}
}
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