source code
/* The Computer Language Benchmarks Game
http://benchmarksgame.alioth.debian.org/
contributed by Isaac Gouy
*/
using System;
class NBody {
public static void Main(String[] args) {
int n = 10000;
if (args.Length > 0) n = Int32.Parse(args[0]);
NBodySystem bodies = new NBodySystem();
Console.WriteLine("{0:f9}",bodies.Energy());
for (int i=0; i<n; i++)
bodies.Advance(0.01);
Console.WriteLine("{0:f9}",bodies.Energy());
}
}
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;
foreach (Body body in bodies) {
px += body.vx * body.mass;
py += body.vy * body.mass;
pz += body.vz * body.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++) {
Body bodyi = bodies[i];
for (int j=i+1; j < bodies.Length; j++) {
Body bodyj = bodies[j];
dx = bodyi.x - bodyj.x;
dy = bodyi.y - bodyj.y;
dz = bodyi.z - bodyj.z;
distance = Math.Sqrt(dx*dx + dy*dy + dz*dz);
mag = dt / (distance * distance * distance);
bodyi.vx -= dx * bodyj.mass * mag;
bodyi.vy -= dy * bodyj.mass * mag;
bodyi.vz -= dz * bodyj.mass * mag;
bodyj.vx += dx * bodyi.mass * mag;
bodyj.vy += dy * bodyi.mass * mag;
bodyj.vz += dz * bodyi.mass * mag;
}
}
foreach (Body body in bodies) {
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 bodyi = bodies[i];
e += 0.5 * bodyi.mass *
( bodyi.vx * bodyi.vx
+ bodyi.vy * bodyi.vy
+ bodyi.vz * bodyi.vz );
for (int j=i+1; j < bodies.Length; j++) {
Body bodyj = bodies[j];
dx = bodyi.x - bodyj.x;
dy = bodyi.y - bodyj.y;
dz = bodyi.z - bodyj.z;
distance = Math.Sqrt(dx*dx + dy*dy + dz*dz);
e -= (bodyi.mass * bodyj.mass) / distance;
}
}
return e;
}
}
class Body {
const double PI = 3.141592653589793;
const double SOLAR_MASS = 4 * PI * PI;
const double DAYS_PER_YEAR = 365.24;
public double x, y, z, vx, vy, vz, mass;
public Body(){}
internal 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;
}
internal 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;
}
internal 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;
}
internal 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;
}
internal static Body Sun() {
Body p = new Body();
p.mass = SOLAR_MASS;
return p;
}
internal Body OffsetMomentum(double px, double py, double pz) {
vx = -px / SOLAR_MASS;
vy = -py / SOLAR_MASS;
vz = -pz / SOLAR_MASS;
return this;
}
}