source code
/* The Computer Language Benchmarks Game
https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
contributed by Jos Hirth,
transliterated from Isaac Gouy and Robert F. Tobler's C# program
+ null safety
*/
import 'dart:math' as Math;
void main(args) {
int n = args.length > 0 ? int.parse(args[0]) : 0;
NBodySystem system = NBodySystem();
print(system.energy().toStringAsFixed(9));
for (int i = 0; i < n; i++) {
system.advance(0.01);
}
print(system.energy().toStringAsFixed(9));
}
class Body {
double x, y, z, vx, vy, vz, mass;
Body(
{this.x = 0.0,
this.y = 0.0,
this.z = 0.0,
this.vx = 0.0,
this.vy = 0.0,
this.vz = 0.0,
this.mass = 0.0});
}
class NBodySystem {
var bodies;
static double solarmass = 4 * Math.pi * Math.pi;
static double daysPeryear = 365.24;
NBodySystem() {
bodies = <Body>[];
bodies.addAll([
// Sun
Body(x: 0.0, y: 0.0, z: 0.0, vx: 0.0, vy: 0.0, vz: 0.0, mass: solarmass),
// Jupiter
Body(
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),
// Saturn
Body(
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),
// Uranus
Body(
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),
// Neptune
Body(
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)
]);
double px = 0.0, py = 0.0, pz = 0.0;
for (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;
}
void advance(double dt) {
for (int na = 0; na < bodies.length; na++) {
Body a = bodies[na];
for (int nb = na + 1; nb < bodies.length; nb++) {
Body b = bodies[nb];
double dx = a.x - b.x, dy = a.y - b.y, dz = a.z - b.z;
double d2 = dx * dx + dy * dy + dz * dz;
double mag = dt / (d2 * Math.sqrt(d2));
a.vx -= dx * b.mass * mag;
b.vx += dx * a.mass * mag;
a.vy -= dy * b.mass * mag;
b.vy += dy * a.mass * mag;
a.vz -= dz * b.mass * mag;
b.vz += dz * a.mass * mag;
}
}
for (var b in bodies) {
b.x += dt * b.vx;
b.y += dt * b.vy;
b.z += dt * b.vz;
}
}
double energy() {
double e = 0.0;
for (int i = 0; i < bodies.length; 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 < bodies.length; 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;
}
}