michael@0: /* The Great Computer Language Shootout
michael@0:    http://shootout.alioth.debian.org/
michael@0:    contributed by Isaac Gouy */
michael@0: 
michael@0: var PI = 3.141592653589793;
michael@0: var SOLAR_MASS = 4 * PI * PI;
michael@0: var DAYS_PER_YEAR = 365.24;
michael@0: 
michael@0: function Body(x,y,z,vx,vy,vz,mass){
michael@0:    this.x = x;
michael@0:    this.y = y;
michael@0:    this.z = z;
michael@0:    this.vx = vx;
michael@0:    this.vy = vy;
michael@0:    this.vz = vz;
michael@0:    this.mass = mass;
michael@0: }
michael@0: 
michael@0: Body.prototype.offsetMomentum = function(px,py,pz) {
michael@0:    this.vx = -px / SOLAR_MASS;
michael@0:    this.vy = -py / SOLAR_MASS;
michael@0:    this.vz = -pz / SOLAR_MASS;
michael@0:    return this;
michael@0: }
michael@0: 
michael@0: function Jupiter(){
michael@0:    return new Body(
michael@0:       4.84143144246472090e+00,
michael@0:       -1.16032004402742839e+00,
michael@0:       -1.03622044471123109e-01,
michael@0:       1.66007664274403694e-03 * DAYS_PER_YEAR,
michael@0:       7.69901118419740425e-03 * DAYS_PER_YEAR,
michael@0:       -6.90460016972063023e-05 * DAYS_PER_YEAR,
michael@0:       9.54791938424326609e-04 * SOLAR_MASS
michael@0:    );
michael@0: }
michael@0: 
michael@0: function Saturn(){
michael@0:    return new Body(
michael@0:       8.34336671824457987e+00,
michael@0:       4.12479856412430479e+00,
michael@0:       -4.03523417114321381e-01,
michael@0:       -2.76742510726862411e-03 * DAYS_PER_YEAR,
michael@0:       4.99852801234917238e-03 * DAYS_PER_YEAR,
michael@0:       2.30417297573763929e-05 * DAYS_PER_YEAR,
michael@0:       2.85885980666130812e-04 * SOLAR_MASS
michael@0:    );
michael@0: }
michael@0: 
michael@0: function Uranus(){
michael@0:    return new Body(
michael@0:       1.28943695621391310e+01,
michael@0:       -1.51111514016986312e+01,
michael@0:       -2.23307578892655734e-01,
michael@0:       2.96460137564761618e-03 * DAYS_PER_YEAR,
michael@0:       2.37847173959480950e-03 * DAYS_PER_YEAR,
michael@0:       -2.96589568540237556e-05 * DAYS_PER_YEAR,
michael@0:       4.36624404335156298e-05 * SOLAR_MASS
michael@0:    );
michael@0: }
michael@0: 
michael@0: function Neptune(){
michael@0:    return new Body(
michael@0:       1.53796971148509165e+01,
michael@0:       -2.59193146099879641e+01,
michael@0:       1.79258772950371181e-01,
michael@0:       2.68067772490389322e-03 * DAYS_PER_YEAR,
michael@0:       1.62824170038242295e-03 * DAYS_PER_YEAR,
michael@0:       -9.51592254519715870e-05 * DAYS_PER_YEAR,
michael@0:       5.15138902046611451e-05 * SOLAR_MASS
michael@0:    );
michael@0: }
michael@0: 
michael@0: function Sun(){
michael@0:    return new Body(0.0, 0.0, 0.0, 0.0, 0.0, 0.0, SOLAR_MASS);
michael@0: }
michael@0: 
michael@0: 
michael@0: function NBodySystem(bodies){
michael@0:    this.bodies = bodies;
michael@0:    var px = 0.0;
michael@0:    var py = 0.0;
michael@0:    var pz = 0.0;
michael@0:    var size = this.bodies.length;
michael@0:    /* BEGIN LOOP */
michael@0:    for (var i=0; i<size; i++){
michael@0:       var b = this.bodies[i];
michael@0:       var m = b.mass;
michael@0:       px += b.vx * m;
michael@0:       py += b.vy * m;
michael@0:       pz += b.vz * m;
michael@0:    }
michael@0:    /* END LOOP */
michael@0:    this.bodies[0].offsetMomentum(px,py,pz);
michael@0: }
michael@0: 
michael@0: NBodySystem.prototype.advance = function(dt){
michael@0:    var dx, dy, dz, distance, mag;
michael@0:    var size = this.bodies.length;
michael@0: 
michael@0:    /* BEGIN LOOP */
michael@0:    for (var i=0; i<size; i++) {
michael@0:       var bodyi = this.bodies[i];
michael@0:       /* BEGIN LOOP */
michael@0:       for (var j=i+1; j<size; j++) {
michael@0:          var bodyj = this.bodies[j];
michael@0:          dx = bodyi.x - bodyj.x;
michael@0:          dy = bodyi.y - bodyj.y;
michael@0:          dz = bodyi.z - bodyj.z;
michael@0: 
michael@0:          distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
michael@0:          mag = dt / (distance * distance * distance);
michael@0: 
michael@0:          bodyi.vx -= dx * bodyj.mass * mag;
michael@0:          bodyi.vy -= dy * bodyj.mass * mag;
michael@0:          bodyi.vz -= dz * bodyj.mass * mag;
michael@0: 
michael@0:          bodyj.vx += dx * bodyi.mass * mag;
michael@0:          bodyj.vy += dy * bodyi.mass * mag;
michael@0:          bodyj.vz += dz * bodyi.mass * mag;
michael@0:       }
michael@0:       /* END LOOP */
michael@0:    }
michael@0:    /* END LOOP */
michael@0: 
michael@0:    /* BEGIN LOOP */
michael@0:    for (var i=0; i<size; i++) {
michael@0:       var body = this.bodies[i];
michael@0:       body.x += dt * body.vx;
michael@0:       body.y += dt * body.vy;
michael@0:       body.z += dt * body.vz;
michael@0:    }
michael@0:    /* END LOOP */
michael@0: }
michael@0: 
michael@0: NBodySystem.prototype.energy = function(){
michael@0:    var dx, dy, dz, distance;
michael@0:    var e = 0.0;
michael@0:    var size = this.bodies.length;
michael@0: 
michael@0:    /* BEGIN LOOP */
michael@0:    for (var i=0; i<size; i++) {
michael@0:       var bodyi = this.bodies[i];
michael@0: 
michael@0:       e += 0.5 * bodyi.mass *
michael@0:          ( bodyi.vx * bodyi.vx
michael@0:          + bodyi.vy * bodyi.vy
michael@0:          + bodyi.vz * bodyi.vz );
michael@0: 
michael@0:       /* BEGIN LOOP */
michael@0:       for (var j=i+1; j<size; j++) {
michael@0:          var bodyj = this.bodies[j];
michael@0:          dx = bodyi.x - bodyj.x;
michael@0:          dy = bodyi.y - bodyj.y;
michael@0:          dz = bodyi.z - bodyj.z;
michael@0: 
michael@0:          distance = Math.sqrt(dx*dx + dy*dy + dz*dz);
michael@0:          e -= (bodyi.mass * bodyj.mass) / distance;
michael@0:       }
michael@0:       /* END LOOP */
michael@0:    }
michael@0:    /* END LOOP */
michael@0:    return e;
michael@0: }
michael@0: 
michael@0: var ret;
michael@0: 
michael@0: /* BEGIN LOOP */
michael@0: for ( var n = 3; n <= 24; n *= 2 ) {
michael@0:     (function(){
michael@0:         var bodies = new NBodySystem( Array(
michael@0:            Sun(),Jupiter(),Saturn(),Uranus(),Neptune()
michael@0:         ));
michael@0:         var max = n * 100;
michael@0:         
michael@0:         ret = bodies.energy();
michael@0: 	/* BEGIN LOOP */
michael@0:         for (var i=0; i<max; i++){
michael@0:             bodies.advance(0.01);
michael@0:         }
michael@0: 	/* END LOOP */
michael@0:         ret = bodies.energy();
michael@0:     })();
michael@0: }
michael@0: /* END LOOP */