| /* 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; |
| } |
| } |
| |