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package main
import (
"encoding/json"
"fmt"
"github.com/gorilla/mux"
"log"
"math"
"net/http"
"strconv"
)
// Defining the constants used in the NFW profile
const (
sigma float64 = 200
f0 float64 = 0.1
G float64 = 4.302e-3
rS float64 = 1e4
)
type result struct {
NFW float64 `json:"NFW"`
}
// The actual NFW profile
// Uses the given distance to the middle of the galaxy to calculate the probability that a star is generated
func rho(x float64, y float64, z float64) float64 {
r := math.Sqrt(math.Pow(x, 2) + math.Pow(y, 2) + math.Pow(z, 2))
a := (1) / (math.Sqrt(2*math.Pi) * sigma)
b := math.Exp(-phi(r) / math.Pow(sigma, 2))
return a * b
}
// A subset of the NFW function in order to handle the 0 case
func phi(x float64) float64 {
if x == 0 {
return -4 * math.Pi * f0 * G * math.Pow(rS, 2)
}
a := -(4 * math.Pi * f0 * G * math.Pow(rS, 3)) / x
b := math.Log(1.0 + (x / rS))
return a * b
}
// NFW is the corresponding HTTP-handler to the NFW Profile
// It uses the given distance to the Midpoint of the galaxy to calculate and return the probability that a star
// is generated.
func NFW(w http.ResponseWriter, r *http.Request) {
params := r.URL.Query()
// parse the parameters
x, _ := strconv.ParseFloat(params.Get("x"), 64)
y, _ := strconv.ParseFloat(params.Get("y"), 64)
z, _ := strconv.ParseFloat(params.Get("z"), 64)
// calculate the NFW-value
var returnValue result = result{rho(x, y, z)}
log.Print(returnValue)
b, err := json.Marshal(returnValue)
if err != nil {
panic(err)
}
// http response writer
w.Header().Set("Content-Type", "application/json")
_, err = fmt.Fprintf(w, "%v", string(b))
if err != nil {
panic(err)
}
}
// Index handles request on the / endpoint
func Index(w http.ResponseWriter, r *http.Request) {
log.Print(fmt.Fprintln(w, "usage: nfw.docker.localhost/NFW?x=<x>&y=<y>&z=<z>"))
}
func main() {
router := mux.NewRouter()
// routes
router.HandleFunc("/", Index).Methods("GET")
router.HandleFunc("/NFW", NFW).Methods("GET")
log.Println("Starting the service on port localhost:8081")
log.Fatal(http.ListenAndServe(":8081", router))
}
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