cube root iterate

gistfile1.go

package main

import (
    "fmt"
    "math/cmplx"
    "math"
)

func equal(x, y complex128) bool {
    delta := 0.0001
    r1, t1 := cmplx.Polar(x)
    r2, t2 := cmplx.Polar(y)
    return math.Abs(r1-r2) < delta && math.Abs(t1-t2) < delta
}

func Cbrt(x complex128) complex128 {
    z := x
    for {
        i := z - (cmplx.Pow(z, 3)-x)/(3*cmplx.Pow(z,2))
        if equal(i, z) {
            return i
        }        
        z = i
    }
}

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