source code
namespace nbody
{
/* The Computer Language Benchmarks Game
https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
contributed by Isaac Gouy
modified by Robert F. Tobler
modified by Eric P. Nusbaum
*/
using System;
public class NBody
{
public static void Main(String[] args)
{
int n = args.Length > 0 ? Int32.Parse(args[0]) : 10000;
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());
}
}
public class Body { public double x, y, z, vx, vy, vz, mass; }
public class NBodySystem
{
private Body[] _bodies;
private Body[] _pairL;
private Body[] _pairR;
private byte bodyCount = 5;
const double Pi = 3.141592653589793;
const double Solarmass = 4 * Pi * Pi;
const double DaysPeryear = 365.24;
public NBodySystem()
{
_bodies = new[]
{
new Body()
{
// Sun
mass = Solarmass,
},
new Body()
{
// Jupiter
x = 4.84143144246472090e+00,
y = -1.16032004402742839e+00,
z = -1.03622044471123109e-01,
vx = 1.66007664274403694e-03*DaysPeryear,
vy = 7.69901118419740425e-03*DaysPeryear,
vz = -6.90460016972063023e-05*DaysPeryear,
mass = 9.54791938424326609e-04*Solarmass,
},
new Body()
{
// Saturn
x = 8.34336671824457987e+00,
y = 4.12479856412430479e+00,
z = -4.03523417114321381e-01,
vx = -2.76742510726862411e-03*DaysPeryear,
vy = 4.99852801234917238e-03*DaysPeryear,
vz = 2.30417297573763929e-05*DaysPeryear,
mass = 2.85885980666130812e-04*Solarmass,
},
new Body()
{
// Uranus
x = 1.28943695621391310e+01,
y = -1.51111514016986312e+01,
z = -2.23307578892655734e-01,
vx = 2.96460137564761618e-03*DaysPeryear,
vy = 2.37847173959480950e-03*DaysPeryear,
vz = -2.96589568540237556e-05*DaysPeryear,
mass = 4.36624404335156298e-05*Solarmass,
},
new Body()
{
// Neptune
x = 1.53796971148509165e+01,
y = -2.59193146099879641e+01,
z = 1.79258772950371181e-01,
vx = 2.68067772490389322e-03*DaysPeryear,
vy = 1.62824170038242295e-03*DaysPeryear,
vz = -9.51592254519715870e-05*DaysPeryear,
mass = 5.15138902046611451e-05*Solarmass,
},
};
_pairL = new Body[(bodyCount * (bodyCount - 1) / 2)];
_pairR = new Body[(bodyCount * (bodyCount - 1) / 2)];
var pi = 0;
for (var i = 0; i < bodyCount - 1; i++)
for (var j = i + 1; j < bodyCount; j++)
{
_pairL[pi] = _bodies[i];
_pairR[pi] = _bodies[j];
pi++;
}
double px = 0.0, py = 0.0, pz = 0.0;
foreach (var b in _bodies)
{
px += b.vx * b.mass; py += b.vy * b.mass; pz += b.vz * b.mass;
}
var sol = _bodies[0];
sol.vx = -px / Solarmass; sol.vy = -py / Solarmass; sol.vz = -pz / Solarmass;
}
public void Advance(double dt)
{
var length = _pairL.Length;
for (int i = 0; i < length; i++)
{
Body bi = _pairL[i], bj = _pairR[i];
double dx = bi.x - bj.x, dy = bi.y - bj.y, dz = bi.z - bj.z;
double d2 = dx * dx + dy * dy + dz * dz;
double mag = dt / (d2 * Math.Sqrt(d2));
bi.vx -= dx * bj.mass * mag; bj.vx += dx * bi.mass * mag;
bi.vy -= dy * bj.mass * mag; bj.vy += dy * bi.mass * mag;
bi.vz -= dz * bj.mass * mag; bj.vz += dz * bi.mass * mag;
}
foreach (var b in _bodies)
{
b.x += dt * b.vx; b.y += dt * b.vy; b.z += dt * b.vz;
}
}
public double Energy()
{
double e = 0.0;
for (int i = 0; i < bodyCount; i++)
{
var 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 < bodyCount; j++)
{
var bj = _bodies[j];
double dx = bi.x - bj.x, dy = bi.y - bj.y, dz = bi.z - bj.z;
e -= (bi.mass * bj.mass) / Math.Sqrt(dx * dx + dy * dy + dz * dz);
}
}
return e;
}
}
}