source code
/* The Computer Language Benchmarks Game
http://benchmarksgame.alioth.debian.org/
contributed by Mark C. Lewis
modified slightly by Chad Whipkey
modified by Robert McKee
*/
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
{
const double PI = Math.PI;
const double SOLAR_MASS = 4 * PI * PI;
const double DAYS_PER_YEAR = 365.24;
private Body[] bodies;
const int bl = 5;
public NBodySystem()
{
bodies = new Body[] {
new Body() { // Sun
mass = SOLAR_MASS,
},
new Body() { // Jupiter
x = 4.84143144246472090e+00,
y = -1.16032004402742839e+00,
z = -1.03622044471123109e-01,
vx = 1.66007664274403694e-03 * DAYS_PER_YEAR,
vy = 7.69901118419740425e-03 * DAYS_PER_YEAR,
vz = -6.90460016972063023e-05 * DAYS_PER_YEAR,
mass = 9.54791938424326609e-04 * SOLAR_MASS,
},
new Body() { // Saturn
x = 8.34336671824457987e+00,
y = 4.12479856412430479e+00,
z = -4.03523417114321381e-01,
vx = -2.76742510726862411e-03 * DAYS_PER_YEAR,
vy = 4.99852801234917238e-03 * DAYS_PER_YEAR,
vz = 2.30417297573763929e-05 * DAYS_PER_YEAR,
mass = 2.85885980666130812e-04 * SOLAR_MASS,
},
new Body() { // Uranus
x = 1.28943695621391310e+01,
y = -1.51111514016986312e+01,
z = -2.23307578892655734e-01,
vx = 2.96460137564761618e-03 * DAYS_PER_YEAR,
vy = 2.37847173959480950e-03 * DAYS_PER_YEAR,
vz = -2.96589568540237556e-05 * DAYS_PER_YEAR,
mass = 4.36624404335156298e-05 * SOLAR_MASS,
},
new Body() { // Neptune
x = 1.53796971148509165e+01,
y = -2.59193146099879641e+01,
z = 1.79258772950371181e-01,
vx = 2.68067772490389322e-03 * DAYS_PER_YEAR,
vy = 1.62824170038242295e-03 * DAYS_PER_YEAR,
vz = -9.51592254519715870e-05 * DAYS_PER_YEAR,
mass = 5.15138902046611451e-05 * SOLAR_MASS,
},
};
double px = 0;
double py = 0;
double pz = 0;
foreach (Body body in bodies)
{
px += body.vx * body.mass;
py += body.vy * body.mass;
pz += body.vz * body.mass;
}
var sol = bodies[0];
sol.vx = -px / SOLAR_MASS;
sol.vy = -py / SOLAR_MASS;
sol.vz = -pz / SOLAR_MASS;
}
public void Advance(double dt)
{
double dx, dy, dz, distance, mag, bim, bjm;
double x, y, z;
for (int i = 0; i < bl; i++)
{
Body bi = bodies[i];
x = bi.x;
y = bi.y;
z = bi.z;
for (int j = i + 1; j < bl; j++)
{
Body bj = bodies[j];
dx = x - bj.x;
dy = y - bj.y;
dz = z - bj.z;
distance = Math.Sqrt(dx * dx + dy * dy + dz * dz);
mag = dt / (distance * distance * distance);
bim = bi.mass * mag;
bjm = bj.mass * mag;
bi.vx -= dx * bjm;
bi.vy -= dy * bjm;
bi.vz -= dz * bjm;
bj.vx += dx * bim;
bj.vy += dy * bim;
bj.vz += dz * bim;
}
bi.x = x + dt * bi.vx;
bi.y = y + dt * bi.vy;
bi.z = z + dt * bi.vz;
}
}
public double Energy()
{
double dx, dy, dz, distance;
double e = 0;
for (int i = 0; i < bl; i++)
{
Body bi = bodies[i];
e += 0.5 * bi.mass * (bi.vx * bi.vx + bi.vy * bi.vy + bi.vz * bi.vz);
for (int j = i + 1; j < bl; j++)
{
Body bj = bodies[j];
dx = bi.x - bj.x;
dy = bi.y - bj.y;
dz = bi.z - bj.z;
distance = Math.Sqrt(dx * dx + dy * dy + dz * dz);
e -= (bi.mass * bj.mass) / distance;
}
}
return e;
}
}
class Body
{
public double x, y, z, vx, vy, vz, mass;
}