source code
/* The Computer Language Benchmarks Game
* https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
*
* contributed by The Go Authors.
* based on C program by Christoph Bauer
* flag.Arg hack by Isaac Gouy
*/
package main
import (
"flag"
"fmt"
"math"
"strconv"
)
var n = 0
type Body struct {
x, y, z, vx, vy, vz, mass float64
}
const (
solarMass = 4 * math.Pi * math.Pi
daysPerYear = 365.24
)
func (b *Body) offsetMomentum(px, py, pz float64) {
b.vx = -px / solarMass
b.vy = -py / solarMass
b.vz = -pz / solarMass
}
type System []*Body
func NewSystem(body []Body) System {
n := make(System, len(body))
for i := 0; i < len(body); i++ {
n[i] = new(Body) // copy to avoid overwriting the inputs
*n[i] = body[i]
}
var px, py, pz float64
for _, body := range n {
px += body.vx * body.mass
py += body.vy * body.mass
pz += body.vz * body.mass
}
n[0].offsetMomentum(px, py, pz)
return n
}
func (sys System) energy() float64 {
var e float64
for i, body := range sys {
e += 0.5 * body.mass *
(body.vx*body.vx + body.vy*body.vy + body.vz*body.vz)
for j := i + 1; j < len(sys); j++ {
body2 := sys[j]
dx := body.x - body2.x
dy := body.y - body2.y
dz := body.z - body2.z
distance := math.Sqrt(dx*dx + dy*dy + dz*dz)
e -= (body.mass * body2.mass) / distance
}
}
return e
}
func (sys System) advance(dt float64) {
for i, body := range sys {
for j := i + 1; j < len(sys); j++ {
body2 := sys[j]
dx := body.x - body2.x
dy := body.y - body2.y
dz := body.z - body2.z
dSquared := dx*dx + dy*dy + dz*dz
distance := math.Sqrt(dSquared)
mag := dt / (dSquared * distance)
body.vx -= dx * body2.mass * mag
body.vy -= dy * body2.mass * mag
body.vz -= dz * body2.mass * mag
body2.vx += dx * body.mass * mag
body2.vy += dy * body.mass * mag
body2.vz += dz * body.mass * mag
}
}
for _, body := range sys {
body.x += dt * body.vx
body.y += dt * body.vy
body.z += dt * body.vz
}
}
var (
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,
}
sun = Body{
mass: solarMass,
}
)
func main() {
flag.Parse()
if flag.NArg() > 0 { n,_ = strconv.Atoi( flag.Arg(0) ) }
system := NewSystem([]Body{sun, jupiter, saturn, uranus, neptune})
fmt.Printf("%.9f\n", system.energy())
for i := 0; i < n; i++ {
system.advance(0.01)
}
fmt.Printf("%.9f\n", system.energy())
}