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package forces
import (
"../structs"
"fmt"
"gopkg.in/cheggaaa/pb.v1"
"math"
)
// forces_acting calculates the force inbetween the two given stars s1 and s2
// The function return the force
func forceActing(s1 structs.Star, s2 structs.Star) structs.Force {
// Gravitational constant
var G = 6.674 * math.Pow(10, -11)
// Distance between the stars
var r21 = math.Sqrt(math.Pow(s2.C.X-s1.C.X, 2) + math.Pow(s2.C.Y-s1.C.Y, 2))
// Unit vector pointing from s1 to s2
rhat := structs.Force{s2.C.X - s1.C.X, s2.C.Y - s1.C.Y}
// Calculate how strong the star is affected
var FScalar = G * (s1.Mass * s2.Mass) / math.Pow(math.Abs(r21), 2)
// Calculate the overall force by combining the scalar and the vector
var Fx = FScalar * rhat.X
var Fy = FScalar * rhat.Y
// Pack the forces in a force structur
F := structs.Force{Fx, Fy}
return F
}
// forces calculates the forces acting in between a given star and all the other stars in a given array.
func forces(stars_arr []structs.Star, nr int) structs.Force {
var force structs.Force
// Iterate over all the stars in the stars_arr
for index := range stars_arr {
// If the current star is not the star itself
if index != nr {
// generate a new force and add it to the overall force of the star
fa := forceActing(stars_arr[nr], stars_arr[index])
stars_arr[nr].F.X += fa.X
stars_arr[nr].F.Y += fa.Y
force.X += fa.X
force.Y += fa.Y
}
}
return force
}
// forcesThread calculates the forces acting on a given amount of stars in a given range for a given slice of stars
// as a go-routine
func forcesThread(starSlice []structs.Star, localRangeStart int, localRangeEnd int, channel chan structs.Star) {
// iterate over the given range
for index := localRangeStart; index < localRangeEnd; index++ {
// Calculate the force acting inbetween the given star and all other stars
var force = forces(starSlice, index)
// create a new star
newStar := structs.Star{
structs.Coord{starSlice[index].C.X, starSlice[index].C.Y},
structs.Force{force.X, force.Y},
starSlice[index].Mass,
}
// push the new Star into the channel
channel <- newStar
}
}
// CalcAllForces calculates all the forces acting inbetween all the stars in the given starSlice slice and
// returns a "new" slice contaning the forces
func CalcAllForces(starSlice []structs.Star) []structs.Star {
// Define a new slice in which the stars (and the forces acting on them) should be saved
var new_slice []structs.Star
fmt.Printf("\n")
// Define a progres-bar
bar := pb.StartNew(len(starSlice)).Prefix("Stars done: ")
bar.SetWidth(80)
// Iterate over all the stars in the original slice
for index := range starSlice {
// Increment the progress-bar
bar.Increment()
// Calculate the force acting inbetween the given star and all other stars
// This utilizes go-routines :D
var force = forces(starSlice, index)
// create a new star
current_star := structs.Star{
structs.Coord{starSlice[index].C.X, starSlice[index].C.Y},
structs.Force{force.X, force.Y},
starSlice[index].Mass,
}
// append the new star to the new slice
new_slice = append(new_slice, current_star)
}
// Print a newline after the progressbar
bar.FinishPrint("")
return new_slice
}
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