133 lines
3.7 KiB
V
133 lines
3.7 KiB
V
// Ported based on https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/nbody-go-3.html
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// Output:
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// -0.169075164
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// -0.169059907
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import math
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const (
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SolarMass = 39.47841760435743197 //4.0 * math.Pi * math.Pi
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DaysPerYear = 365.24
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N = 5
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)
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struct Position {
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pub mut:
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x f64
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y f64
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z f64
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}
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struct Momentum {
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pub mut:
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x f64
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y f64
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z f64
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m f64
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}
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struct System {
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pub mut:
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v []Momentum
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s []Position
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}
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fn advance(sys mut System, dt f64) {
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for i := 0; i < N - 1; i++ {
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mut _vx := sys.v[i].x
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mut _vy := sys.v[i].y
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mut _vz := sys.v[i].z
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for j := i + 1; j < N; j++ {
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dx := sys.s[i].x - sys.s[j].x
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dy := sys.s[i].y - sys.s[j].y
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dz := sys.s[i].z - sys.s[j].z
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dsquared := dx * dx + dy * dy + dz * dz
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distance := math.sqrt(dsquared)
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mag := (dt / (dsquared * distance))
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mi := sys.v[i].m
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_vx -= dx * sys.v[j].m * mag
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_vy -= dy * sys.v[j].m * mag
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_vz -= dz * sys.v[j].m * mag
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sys.v[j].x += dx * mi * mag
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sys.v[j].y += dy * mi * mag
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sys.v[j].z += dz * mi * mag
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}
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sys.v[i].x = _vx
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sys.v[i].y = _vy
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sys.v[i].z = _vz
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}
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for i := 0; i < N; i++ {
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sys.s[i].x += dt * sys.v[i].x
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sys.s[i].y += dt * sys.v[i].y
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sys.s[i].z += dt * sys.v[i].z
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}
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}
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fn offsetmomentum(sys mut System) {
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mut px := f64(0)
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mut py := f64(0)
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mut pz := f64(0)
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for i := 0; i < N; i++ {
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px += sys.v[i].x * sys.v[i].m
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py += sys.v[i].y * sys.v[i].m
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pz += sys.v[i].z * sys.v[i].m
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}
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sys.v[0].x = -px / SolarMass
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sys.v[0].y = -py / SolarMass
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sys.v[0].z = -pz / SolarMass
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}
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fn energy(sys System) f64 {
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mut e := f64(0)
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for i := 0; i < N; i++ {
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e += 0.5 * sys.v[i].m * (sys.v[i].x * sys.v[i].x + sys.v[i].y * sys.v[i].y + sys.v[i].z * sys.v[i].z)
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for j := i + 1; j < N; j++ {
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dx := sys.s[i].x - sys.s[j].x
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dy := sys.s[i].y - sys.s[j].y
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dz := sys.s[i].z - sys.s[j].z
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distance := math.sqrt(dx * dx + dy * dy + dz * dz)
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e -= (sys.v[i].m * sys.v[j].m) / distance
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}
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}
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return e
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}
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fn arr_momentum() []Momentum {
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return [
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Momentum {0.0, 0.0, 0.0, SolarMass},
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Momentum {1.66007664274403694e-03 * DaysPerYear, 7.69901118419740425e-03 * DaysPerYear, -6.90460016972063023e-05 * DaysPerYear, 9.54791938424326609e-04 * SolarMass},
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Momentum {-2.76742510726862411e-03 * DaysPerYear, 4.99852801234917238e-03 * DaysPerYear, 2.30417297573763929e-05 * DaysPerYear, 2.85885980666130812e-04 * SolarMass},
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Momentum {2.96460137564761618e-03 * DaysPerYear, 2.37847173959480950e-03 * DaysPerYear, -2.96589568540237556e-05 * DaysPerYear, 4.36624404335156298e-05 * SolarMass},
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Momentum {2.68067772490389322e-03 * DaysPerYear, 1.62824170038242295e-03 * DaysPerYear, -9.51592254519715870e-05 * DaysPerYear, 5.15138902046611451e-05 * SolarMass},
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]
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}
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pub fn arr_position() []Position {
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return [
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Position {0.0, 0.0, 0.0},
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Position {4.84143144246472090e+00, -1.16032004402742839e+00, -1.03622044471123109e-01},
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Position {8.34336671824457987e+00, 4.12479856412430479e+00, -4.03523417114321381e-01},
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Position {1.28943695621391310e+01, -1.51111514016986312e+01, -2.23307578892655734e-01},
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Position {1.53796971148509165e+01, -2.59193146099879641e+01, 1.79258772950371181e-01},
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]
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}
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fn main() {
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sys := &System {arr_momentum(), arr_position()}
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offsetmomentum(mut sys)
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println('${energy(sys):.9f}') //-0.169075164
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for i := 0; i < 50000000; i++ {
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advance(mut sys, 0.01)
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}
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println('${energy(sys):.9f}') //-0.169059907
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}
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