#!/usr/bin/java --source 11 public final class nbody { public static void main(String[] args) { NBodySystem bodies = new NBodySystem(); for (int n = 1; n <= 5; n++) { System.out.printf("%.9f\n", bodies.energy()); for (int i = 0; i < 100000; i++) bodies.advance(0.01); } System.out.printf("%.9f\n", bodies.energy()); } } final class NBodySystem { private static final int LENGTH = 5; 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 < 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) { Body[] b = bodies; for(int i=0; i < LENGTH-1; ++i) { Body iBody = b[i]; double iMass = iBody.mass; double ix = iBody.x, iy = iBody.y, iz = iBody.z; for(int j=i+1; j < LENGTH; ++j) { Body jBody = b[j]; double dx = ix - jBody.x; double dy = iy - jBody.y; double dz = iz - jBody.z; double dSquared = dx * dx + dy * dy + dz * dz; double distance = Math.sqrt(dSquared); double mag = dt / (dSquared * distance); double jMass = jBody.mass; iBody.vx -= dx * jMass * mag; iBody.vy -= dy * jMass * mag; iBody.vz -= dz * jMass * mag; jBody.vx += dx * iMass * mag; jBody.vy += dy * iMass * mag; jBody.vz += dz * iMass * mag; } } for(int i=0; i < LENGTH; ++i) { Body body = b[i]; body.x += dt * body.vx; body.y += dt * body.vy; body.z += dt * body.vz; } } public double energy(){ double dx, dy, dz, distance; double e = 0.0; for (int i=0; i < bodies.length; ++i) { Body iBody = bodies[i]; e += 0.5 * iBody.mass * ( iBody.vx * iBody.vx + iBody.vy * iBody.vy + iBody.vz * iBody.vz ); for (int j=i+1; j < bodies.length; ++j) { Body jBody = bodies[j]; dx = iBody.x - jBody.x; dy = iBody.y - jBody.y; dz = iBody.z - jBody.z; distance = Math.sqrt(dx*dx + dy*dy + dz*dz); e -= (iBody.mass * jBody.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; } }