👍 go run surface.go > sin.svg

package main

import (
  "fmt"
  "math"
)

const (
  width, height = 600, 320
  cells = 100
  xyrange = 30.0
  xyscale = width/2/xyrange
  zscale = height * 0.4
  angle = math.Pi/6
)

var sin30, cos30 = math.Sin(angle), math.Cos(angle) 

func main() {
  fmt.Printf("<svg xmlns='http://www.w3.org/2000/svg' " + "style='stroke: grey; fill: white; stroke-witch: 0.7' " + "width='%d' height='%d'>", width, height)
  for i := 0; i < cells; i++ {
    for j := 0; j < cells; j++ {
      ax, ay := corner(i+1, j)
      bx, by := corner(i, j)
      cx, cy := corner(i, j+1)
      dx, dy := corner(i+1, j+1)
      fmt.Printf("<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n", ax, ay, bx, by, cx, cy, dx, dy)
    }
  }
  fmt.Println("</svg>")
}

func corner(i, j int) (float64, float64) {
  x := xyrange * (float64(i)/cells - 0.5)
  y := xyrange * (float64(j)/cells - 0.5)
  z := f(x, y)
  sx := width/2 + (x-y)*cos30*xyscale
  sy := height/2 + (x+y)*sin30*xyscale - z*zscale
  return sx, sy
}

func f(x, y float64) float64 {
  r := math.Hypot(x, y)
  return math.Sin(r) / r
}


    

ch3.2 Floating-Point Numbers p78/59 of