source code
/* The Computer Language Benchmarks Game
http://benchmarksgame.alioth.debian.org/
mostly auto-converted from Mark C. Lewis's Java #2 program
*/
object nbody {
@JvmStatic fun main(args: Array<String>) {
val n = Integer.parseInt(args[0])
val bodies = NBodySystem()
System.out.printf("%.9f\n", bodies.energy())
for (i in 0 until n)
bodies.advance(0.01)
System.out.printf("%.9f\n", bodies.energy())
}
}
internal class NBodySystem {
private val bodies: Array<Body>
init {
bodies = arrayOf(Body.sun(), Body.jupiter(), Body.saturn(), Body.uranus(), Body.neptune())
var px = 0.0
var py = 0.0
var pz = 0.0
for (i in bodies.indices) {
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)
}
fun advance(dt: Double) {
for (i in bodies.indices) {
val iBody = bodies[i]
for (j in i + 1 until bodies.size) {
val dx = iBody.x - bodies[j].x
val dy = iBody.y - bodies[j].y
val dz = iBody.z - bodies[j].z
val dSquared = dx * dx + dy * dy + dz * dz
val distance = Math.sqrt(dSquared)
val mag = dt / (dSquared * distance)
iBody.vx -= dx * bodies[j].mass * mag
iBody.vy -= dy * bodies[j].mass * mag
iBody.vz -= dz * bodies[j].mass * mag
bodies[j].vx += dx * iBody.mass * mag
bodies[j].vy += dy * iBody.mass * mag
bodies[j].vz += dz * iBody.mass * mag
}
}
for (body in bodies) {
body.x += dt * body.vx
body.y += dt * body.vy
body.z += dt * body.vz
}
}
fun energy(): Double {
var dx: Double
var dy: Double
var dz: Double
var distance: Double
var e = 0.0
for (i in bodies.indices) {
val iBody = bodies[i]
e += 0.5 * iBody.mass *
(iBody.vx * iBody.vx
+ iBody.vy * iBody.vy
+ iBody.vz * iBody.vz)
for (j in i + 1 until bodies.size) {
val 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
}
}
internal class Body {
var x: Double = 0.toDouble()
var y: Double = 0.toDouble()
var z: Double = 0.toDouble()
var vx: Double = 0.toDouble()
var vy: Double = 0.toDouble()
var vz: Double = 0.toDouble()
var mass: Double = 0.toDouble()
fun offsetMomentum(px: Double, py: Double, pz: Double): Body {
vx = -px / SOLAR_MASS
vy = -py / SOLAR_MASS
vz = -pz / SOLAR_MASS
return this
}
companion object {
val PI = 3.141592653589793
val SOLAR_MASS = 4.0 * PI * PI
val DAYS_PER_YEAR = 365.24
fun jupiter(): Body {
val p = 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
}
fun saturn(): Body {
val p = 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
}
fun uranus(): Body {
val p = 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
}
fun neptune(): Body {
val p = 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
}
fun sun(): Body {
val p = Body()
p.mass = SOLAR_MASS
return p
}
}
}
notes, command-line, and program output
NOTES:
64-bit Ubuntu quad core
Kotlin version 1.2.30-release-78 (JRE 10+46)
java 10 2018-03-20
Java(TM) SE Runtime Environment 18.3 (build 10+46)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10+46, mixed mode)
Wed, 21 Mar 2018 23:43:35 GMT
MAKE:
mv nbody.kotlin-2.kotlin nbody.kt
/opt/src/kotlin-1.2.30/bin/kotlinc nbody.kt -d nbody.jar
6.19s to complete and log all make actions
COMMAND LINE:
/opt/src/jdk-10/bin/java -Xbootclasspath/a:/opt/src/kotlin-1.2.30/lib/kotlin-stdlib.jar:./nbody.jar nbody 50000000
PROGRAM OUTPUT:
-0.169075164
-0.169059907