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carun/nbody.d

Created May 17, 2018 23:24
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nbody.d
import std.stdio; [59/187]
// import std.math;
import core.stdc.stdio;
import core.stdc.math;
enum pi = 3.141592653589793;
enum solar_mass = (4 * pi * pi);
enum days_per_year = 365.24;
struct Planet {
double x, y, z;
double vx, vy, vz;
double mass;
}
void advance(Planet[] bodies, double dt)
{
foreach (i; 0 .. bodies.length) {
auto b = &(bodies[i]);
foreach (j; i+1 .. bodies.length) {
auto b2 = &(bodies[j]);
auto dx = b.x - b2.x;
auto dy = b.y - b2.y;
auto dz = b.z - b2.z;
auto distance = sqrt(dx * dx + dy * dy + dz * dz);
auto mag = dt / (distance * distance * distance);
b.vx -= dx * b2.mass * mag;
b.vy -= dy * b2.mass * mag;
b.vz -= dz * b2.mass * mag;
b2.vx += dx * b.mass * mag;
b2.vy += dy * b.mass * mag;
b2.vz += dz * b.mass * mag;
}
}
foreach (i; 0 .. bodies.length) {
auto b = &(bodies[i]);
b.x += dt * b.vx;
b.y += dt * b.vy;
b.z += dt * b.vz;
}
}
double energy(Planet[] bodies)
{
double e = 0.0;
foreach (i; 0 .. bodies.length) {
auto b = &(bodies[i]);
e += 0.5 * b.mass * (b.vx * b.vx + b.vy * b.vy + b.vz * b.vz);
foreach (j; i+1 .. bodies.length) {
auto b2 = &(bodies[j]);
auto dx = b.x - b2.x;
auto dy = b.y - b2.y;
auto dz = b.z - b2.z;
auto distance = sqrt(dx * dx + dy * dy + dz * dz);
e -= (b.mass * b2.mass) / distance;
}
}
return e;
}
void offset_momentum(Planet[] bodies)
{
double px = 0.0, py = 0.0, pz = 0.0;
foreach (i; 0 .. bodies.length) {
px += bodies[i].vx * bodies[i].mass;
py += bodies[i].vy * bodies[i].mass;
pz += bodies[i].vz * bodies[i].mass;
}
bodies[0].vx = - px / solar_mass;
bodies[0].vy = - py / solar_mass;
bodies[0].vz = - pz / solar_mass;
}
enum NBODIES = 5;
Planet[NBODIES] bodies = [
{ /* sun */
x: 0.0, y: 0.0, z: 0.0, vx: 0.0, vy: 0.0, vz: 0.0, mass:solar_mass
},
{ /* jupiter */
4.84143144246472090e+00,
-1.16032004402742839e+00,
-1.03622044471123109e-01,
1.66007664274403694e-03 * days_per_year,
7.69901118419740425e-03 * days_per_year,
-6.90460016972063023e-05 * days_per_year,
9.54791938424326609e-04 * solar_mass
},
{ /* saturn */
8.34336671824457987e+00,
4.12479856412430479e+00,
-4.03523417114321381e-01,
-2.76742510726862411e-03 * days_per_year,
4.99852801234917238e-03 * days_per_year,
2.30417297573763929e-05 * days_per_year,
2.85885980666130812e-04 * solar_mass
},
{ /* uranus */
1.28943695621391310e+01,
-1.51111514016986312e+01,
-2.23307578892655734e-01,
2.96460137564761618e-03 * days_per_year,
2.37847173959480950e-03 * days_per_year,
-2.96589568540237556e-05 * days_per_year,
4.36624404335156298e-05 * solar_mass
},
{ /* neptune */
1.53796971148509165e+01,
-2.59193146099879641e+01,
1.79258772950371181e-01,
2.68067772490389322e-03 * days_per_year,
1.62824170038242295e-03 * days_per_year,
-9.51592254519715870e-05 * days_per_year,
5.15138902046611451e-05 * solar_mass
}
];
void main(string[] args)
{
import std.conv;
int n = to!(int)(args[1]);
offset_momentum(bodies);
printf("%.9f\n", energy(bodies));
foreach (i; 0 .. n)
advance(bodies, 0.01);
printf("%.9f\n", energy(bodies));
}
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