package main
import (
"bytes"
"encoding/base64"
"flag"
"fmt"
"image/color"
"log"
"math/rand"
"net/http"
"go-hep.org/x/hep/hplot"
"golang.org/x/net/websocket"
"gonum.org/v1/plot/plotter"
"gonum.org/v1/plot/vg"
"gonum.org/v1/plot/vg/draw"
"gonum.org/v1/plot/vg/vgimg"
)
func main() {
log.SetPrefix("monte-carlo: ")
log.SetFlags(0)
n := flag.Int("n", 1e7, "number of samples")
flag.Parse()
srv := newServer()
go srv.pi(*n)
http.HandleFunc("/", plotHandle)
http.Handle("/data", websocket.Handler(srv.dataHandler))
log.Printf("listening on :8080...")
err := http.ListenAndServe(":8080", nil)
if err != nil {
log.Fatal(err)
}
}
func (srv *server) pi(samples int) {
for i := 0; i < samples; i++ {
x := rand.Float64()
y := rand.Float64()
srv.datac <- [2]float64{x, y}
}
}
func plotHandle(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, page)
}
func (srv *server) dataHandler(ws *websocket.Conn) {
for data := range srv.plots {
err := websocket.JSON.Send(ws, data)
if err != nil {
log.Printf("error sending data: %v\n", err)
}
}
}
type server struct {
in plotter.XYs // points inside the circle
out plotter.XYs // points outside the circle
n int // number of samples
datac chan [2]float64 // channel of (x,y) points randomly drawn
plots chan wplot // channel of base64-encoded PNG plots
}
func newServer() *server {
srv := &server{
in: make(plotter.XYs, 0, 1024),
out: make(plotter.XYs, 0, 1024),
datac: make(chan [2]float64),
plots: make(chan wplot),
}
go srv.run()
return srv
}
func (srv *server) run() {
for v := range srv.datac {
srv.n++
x := v[0]
y := v[1]
d2 := x*x + y*y
pt := Point{x, y}
switch {
case d2 < 1:
srv.in = append(srv.in, pt)
default:
srv.out = append(srv.out, pt)
}
switch {
case srv.n < 1e1:
if srv.n%1e0 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e2:
if srv.n%1e1 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e3:
if srv.n%1e2 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e4:
if srv.n%1e3 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e5:
if srv.n%1e4 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e6:
if srv.n%1e5 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n < 1e7:
if srv.n%1e6 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
case srv.n > 1e7:
if srv.n%1e7 == 0 {
srv.plots <- plot(srv.n, srv.in, srv.out)
}
}
}
}
func plot(n int, in, out plotter.XYs) wplot {
radius := vg.Points(0.1)
p := hplot.New()
p.X.Label.Text = "x"
p.X.Min = 0
p.X.Max = 1
p.Y.Label.Text = "y"
p.Y.Min = 0
p.Y.Max = 1
pi := 4 * float64(len(in)) / float64(n)
p.Title.Text = fmt.Sprintf("n = %d\nπ = %v", n, pi)
sin, err := hplot.NewScatter(in)
if err != nil {
log.Fatal(err)
}
sin.Color = color.RGBA{255, 0, 0, 255} // red
sin.Radius = radius
sout, err := hplot.NewScatter(out)
if err != nil {
log.Fatal(err)
}
sout.Color = color.RGBA{0, 0, 255, 255} // blue
sout.Radius = radius
p.Add(sin, sout, hplot.NewGrid())
return wplot{Plot: renderImg(p)}
}
func renderImg(p *hplot.Plot) string {
size := 20 * vg.Centimeter
canvas := vgimg.PngCanvas{vgimg.New(size, size)}
p.Draw(draw.New(canvas))
out := new(bytes.Buffer)
_, err := canvas.WriteTo(out)
if err != nil {
log.Fatal(err)
}
return base64.StdEncoding.EncodeToString(out.Bytes())
}
type wplot struct {
Plot string `json:"plot"`
}
type Point struct {
X, Y float64
}
const page = `
Monte Carlo
`