github.com/spotify/syslog-redirector-golang@v0.0.0-20140320174030-4859f03d829a/misc/tour/solutions/complexcube.go (about)

     1  // Copyright 2012 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build ignore
     6  
     7  package main
     8  
     9  import (
    10  	"fmt"
    11  	"math/cmplx"
    12  )
    13  
    14  const delta = 1e-10
    15  
    16  func Cbrt(x complex128) complex128 {
    17  	z := x
    18  	for {
    19  		n := z - (z*z*z-x)/(3*z*z)
    20  		if cmplx.Abs(n-z) < delta {
    21  			break
    22  		}
    23  		z = n
    24  	}
    25  	return z
    26  }
    27  
    28  func main() {
    29  	const x = 2
    30  	mine, theirs := Cbrt(x), cmplx.Pow(x, 1./3.)
    31  	fmt.Println(mine, theirs, mine-theirs)
    32  }