/* The Computer Language Shootout   http://shootout.alioth.debian.org/   contributed by Isaac Gouy*/object nbody {    def main(args: Array[String]) = {      var n = Integer.parseInt(args(0))      Console.printf("%.9f\n", JovianSystem.energy )      while (n > 0) { JovianSystem.advance(0.01); n = n-1 }      Console.printf("%.9f\n", JovianSystem.energy )   } }abstract class NBodySystem {   def energy() = {      var e = 0.0      for (val i <- Iterator.range(0,bodies.length)){         e = 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 (val j <- Iterator.range(i+1,bodies.length)){            val dx = bodies(i).x - bodies(j).x            val dy = bodies(i).y - bodies(j).y            val dz = bodies(i).z - bodies(j).z            val distance = Math.sqrt(dx*dx + dy*dy + dz*dz)            e = e - (bodies(i).mass * bodies(j).mass) / distance         }      }      e   }   def advance(dt: double) = {      var i = 0      while (i < bodies.length){         var j = i+1         while (j < bodies.length){            val dx = bodies(i).x - bodies(j).x            val dy = bodies(i).y - bodies(j).y            val dz = bodies(i).z - bodies(j).z            val distance = Math.sqrt(dx*dx + dy*dy + dz*dz)            val mag = dt / (distance * distance * distance)            bodies(i).vx = bodies(i).vx - dx * bodies(j).mass * mag            bodies(i).vy = bodies(i).vy - dy * bodies(j).mass * mag            bodies(i).vz = bodies(i).vz - dz * bodies(j).mass * mag            bodies(j).vx = bodies(j).vx + dx * bodies(i).mass * mag            bodies(j).vy = bodies(j).vy + dy * bodies(i).mass * mag            bodies(j).vz = bodies(j).vz + dz * bodies(i).mass * mag            j = j+1         }         i = i+1      }      i = 0      while (i < bodies.length){         bodies(i).x = bodies(i).x + dt * bodies(i).vx         bodies(i).y = bodies(i).y + dt * bodies(i).vy         bodies(i).z = bodies(i).z + dt * bodies(i).vz         i = i+1      }   }   protected val bodies: Array[Body]   class Body(){      var x = 0.0; var y = 0.0; var z = 0.0;      var vx = 0.0; var vy = 0.0; var vz = 0.0      var mass = 0.0   }}object JovianSystem extends NBodySystem {   protected val bodies = initialValues   private def initialValues() = {       val PI = 3.141592653589793      val SOLAR_MASS = 4 * PI * PI      val DAYS_PER_YEAR = 365.24      val sun = new Body      sun.mass = SOLAR_MASS      val jupiter = new Body      jupiter.x = 4.84143144246472090e+00       jupiter.y = -1.16032004402742839e+00      jupiter.z = -1.03622044471123109e-01      jupiter.vx = 1.66007664274403694e-03 * DAYS_PER_YEAR      jupiter.vy = 7.69901118419740425e-03 * DAYS_PER_YEAR      jupiter.vz = -6.90460016972063023e-05 * DAYS_PER_YEAR      jupiter.mass = 9.54791938424326609e-04 * SOLAR_MASS      val saturn = new Body      saturn.x = 8.34336671824457987e+00      saturn.y = 4.12479856412430479e+00      saturn.z = -4.03523417114321381e-01      saturn.vx = -2.76742510726862411e-03 * DAYS_PER_YEAR      saturn.vy = 4.99852801234917238e-03 * DAYS_PER_YEAR      saturn.vz = 2.30417297573763929e-05 * DAYS_PER_YEAR      saturn.mass = 2.85885980666130812e-04 * SOLAR_MASS      val uranus = new Body      uranus.x = 1.28943695621391310e+01      uranus.y = -1.51111514016986312e+01      uranus.z = -2.23307578892655734e-01      uranus.vx = 2.96460137564761618e-03 * DAYS_PER_YEAR      uranus.vy = 2.37847173959480950e-03 * DAYS_PER_YEAR      uranus.vz = -2.96589568540237556e-05 * DAYS_PER_YEAR      uranus.mass = 4.36624404335156298e-05 * SOLAR_MASS      val neptune = new Body      neptune.x = 1.53796971148509165e+01      neptune.y = -2.59193146099879641e+01      neptune.z = 1.79258772950371181e-01      neptune.vx = 2.68067772490389322e-03 * DAYS_PER_YEAR      neptune.vy = 1.62824170038242295e-03 * DAYS_PER_YEAR      neptune.vz = -9.51592254519715870e-05 * DAYS_PER_YEAR      neptune.mass = 5.15138902046611451e-05  * SOLAR_MASS      val initialValues = Array ( sun, jupiter, saturn, uranus, neptune )      var px = 0.0; var py = 0.0; var pz = 0.0;      for (val b <- initialValues){         px = px + (b.vx * b.mass)         py = py + (b.vy * b.mass)         pz = pz + (b.vz * b.mass)      }      sun.vx = -px / SOLAR_MASS      sun.vy = -py / SOLAR_MASS      sun.vz = -pz / SOLAR_MASS      initialValues   }}