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package main
import (
"encoding/json"
"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
)
// 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(r float64) float64 {
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 := mux.Vars(r)
distanceToMidpoint, err := strconv.ParseFloat(params["r"], 64)
if err != nil {
panic(err)
}
var returnValue float64 = rho(distanceToMidpoint)
err = json.NewEncoder(w).Encode(returnValue)
if err != nil {
panic(err)
}
}
func main() {
router := mux.NewRouter()
router.HandleFunc("/NFW/{r}", NFW).Methods("GET")
log.Fatal(http.ListenAndServe(":8000", router))
}
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