http://tour.golang.org/#47 A Tour of Go Advanced Exercise: Complex cube roots Let's explore Go's built-in support for complex numbers via the complex64 and complex128 types. For cube roots, Newton's method amounts to repeating: Find the cube root of 2, just to make sure the algorithm works. There is a Pow function in the math/cmplx package.

gistfile1.go

package main

import "fmt"
import "math/cmplx"

func Cbrt(x complex128) complex128 {
    z := complex128(2)
    s := complex128(0)
    for {
        z = z - (cmplx.Pow(z, 3) - x)/(3 * cmplx.Pow(z, 2))
        if cmplx.Abs(s - z) < 1e17 {
            break           
        }
        s = z
    }
    return z
}

func main() {
    fmt.Println(Cbrt(2))
}

package main

import (
    "fmt"
    "math/cmplx"
)

func Cbrt(x complex128) complex128 {
    z := x
    for cmplx.Pow(z, 3) != x {
        z = z - (z * z * z - x) / (3 * z * z)
    }
    return z
}

func main() {
    fmt.Println(Cbrt(2), "=?" ,cmplx.Pow(2, 1./3))
}