1 files changed, 129 insertions, 0 deletions
diff --git a/v_windows/v/old/examples/nbody.v b/v_windows/v/old/examples/nbody.v
new file mode 100644
index 0000000..0f719e8
--- /dev/null
+++ b/v_windows/v/old/examples/nbody.v
@@ -0,0 +1,129 @@
+// Ported based on https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/nbody-go-3.html
+// Output:
+// -0.169075164
+// -0.169059907
+import math
+
+const (
+	solar_mass    = 39.47841760435743197 // 4.0 * math.Pi * math.Pi
+	days_per_year = 365.24
+	c_n           = 5
+)
+
+struct Position {
+pub mut:
+	x f64
+	y f64
+	z f64
+}
+
+struct Momentum {
+pub mut:
+	x f64
+	y f64
+	z f64
+	m f64
+}
+
+struct System {
+pub mut:
+	v []Momentum
+	s []Position
+}
+
+fn advance(mut sys System, dt f64) {
+	for i in 0 .. c_n - 1 {
+		mut vx := sys.v[i].x
+		mut vy := sys.v[i].y
+		mut vz := sys.v[i].z
+
+		for j := i + 1; j < c_n; j++ {
+			dx := sys.s[i].x - sys.s[j].x
+			dy := sys.s[i].y - sys.s[j].y
+			dz := sys.s[i].z - sys.s[j].z
+
+			dsquared := dx * dx + dy * dy + dz * dz
+			distance := math.sqrt(dsquared)
+			mag := (dt / (dsquared * distance))
+			mi := sys.v[i].m
+
+			vx -= dx * sys.v[j].m * mag
+			vy -= dy * sys.v[j].m * mag
+			vz -= dz * sys.v[j].m * mag
+
+			sys.v[j].x += dx * mi * mag
+			sys.v[j].y += dy * mi * mag
+			sys.v[j].z += dz * mi * mag
+		}
+		sys.v[i].x = vx
+		sys.v[i].y = vy
+		sys.v[i].z = vz
+	}
+
+	for i in 0 .. c_n {
+		sys.s[i].x += dt * sys.v[i].x
+		sys.s[i].y += dt * sys.v[i].y
+		sys.s[i].z += dt * sys.v[i].z
+	}
+}
+
+fn offsetmomentum(mut sys System) {
+	mut px := f64(0)
+	mut py := f64(0)
+	mut pz := f64(0)
+
+	for i in 0 .. c_n {
+		px += sys.v[i].x * sys.v[i].m
+		py += sys.v[i].y * sys.v[i].m
+		pz += sys.v[i].z * sys.v[i].m
+	}
+	sys.v[0].x = -px / solar_mass
+	sys.v[0].y = -py / solar_mass
+	sys.v[0].z = -pz / solar_mass
+}
+
+fn energy(sys System) f64 {
+	mut e := f64(0)
+	for i in 0 .. c_n {
+		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)
+		for j := i + 1; j < c_n; j++ {
+			dx := sys.s[i].x - sys.s[j].x
+			dy := sys.s[i].y - sys.s[j].y
+			dz := sys.s[i].z - sys.s[j].z
+			distance := math.sqrt(dx * dx + dy * dy + dz * dz)
+			e -= (sys.v[i].m * sys.v[j].m) / distance
+		}
+	}
+	return e
+}
+
+fn arr_momentum() []Momentum {
+	return [
+		Momentum{0.0, 0.0, 0.0, solar_mass},
+		Momentum{1.66007664274403694e-03 * days_per_year, 7.69901118419740425e-03 * days_per_year, -6.90460016972063023e-05 * days_per_year, 9.54791938424326609e-04 * solar_mass},
+		Momentum{-2.76742510726862411e-03 * days_per_year, 4.99852801234917238e-03 * days_per_year, 2.30417297573763929e-05 * days_per_year, 2.85885980666130812e-04 * solar_mass},
+		Momentum{2.96460137564761618e-03 * days_per_year, 2.37847173959480950e-03 * days_per_year, -2.96589568540237556e-05 * days_per_year, 4.36624404335156298e-05 * solar_mass},
+		Momentum{2.68067772490389322e-03 * days_per_year, 1.62824170038242295e-03 * days_per_year, -9.51592254519715870e-05 * days_per_year, 5.15138902046611451e-05 * solar_mass},
+	]
+}
+
+fn arr_position() []Position {
+	return [
+		Position{0.0, 0.0, 0.0},
+		Position{4.84143144246472090e+00, -1.16032004402742839e+00, -1.03622044471123109e-01},
+		Position{8.34336671824457987e+00, 4.12479856412430479e+00, -4.03523417114321381e-01},
+		Position{1.28943695621391310e+01, -1.51111514016986312e+01, -2.23307578892655734e-01},
+		Position{1.53796971148509165e+01, -2.59193146099879641e+01, 1.79258772950371181e-01},
+	]
+}
+
+fn main() {
+	mut sys := &System{arr_momentum(), arr_position()}
+	offsetmomentum(mut sys)
+	println('${energy(sys):.9f}') //-0.169075164
+	for _ in 0 .. 50_000_000 {
+		advance(mut sys, 0.01)
+	}
+	println('${energy(sys):.9f}') //-0.169059907
+}