牛顿迭代闭包版

gistfile1.go

package main

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

func equal(x, y complex128) bool {
	delta := 0.000001
	r1, t1 := cmplx.Polar(x)
	r2, t2 := cmplx.Polar(y)
	return math.Abs(r1-r2) < delta && math.Abs(t1-t2) < delta
}

func Y(x complex128) (r func(a complex128) (r2 complex128)) {
	return func(z complex128) (r complex128) {
		r = z - (cmplx.Pow(z, 3)-x)/(3*cmplx.Pow(z, 2))
		return
	}
}

func Cbrt(x complex128, f func(a complex128) (r complex128)) complex128 {
	if equal(f(x), x) {
		return x
	}
	return Cbrt(f(x), f)
}

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