Skip to content

Instantly share code, notes, and snippets.

@cereal-s
Forked from abesto/gist:3476594
Created November 25, 2016 16:00
Show Gist options
  • Save cereal-s/4346df99d116786a3b54036b2e84a728 to your computer and use it in GitHub Desktop.
Save cereal-s/4346df99d116786a3b54036b2e84a728 to your computer and use it in GitHub Desktop.
Go: Newton's method for square root
/*
A Tour of Go: page 44
http://tour.golang.org/#44
Exercise: Loops and Functions
As a simple way to play with functions and loops, implement the square root function using Newton's method.
In this case, Newton's method is to approximate Sqrt(x) by picking a starting point z and then repeating: z - (z*z - x) / (2 * z)
To begin with, just repeat that calculation 10 times and see how close you get to the answer for various values (1, 2, 3, ...).
Next, change the loop condition to stop once the value has stopped changing (or only changes by a very small delta). See if that's more or fewer iterations. How close are you to the math.Sqrt?
Hint: to declare and initialize a floating point value, give it floating point syntax or use a conversion:
z := float64(1)
z := 1.0
*/
package main
import (
"fmt"
"math"
)
const DELTA = 0.0000001
const INITIAL_Z = 100.0
func Sqrt(x float64) (z float64) {
z = INITIAL_Z
step := func() float64 {
return z - (z*z - x) / (2 * z)
}
for zz := step(); math.Abs(zz - z) > DELTA
{
z = zz
zz = step()
}
return
}
func main() {
fmt.Println(Sqrt(500))
fmt.Println(math.Sqrt(500))
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment