| // Copyright 2012 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // +build ignore |
| |
| package main |
| |
| import ( |
| "fmt" |
| "math" |
| ) |
| |
| type ErrNegativeSqrt float64 |
| |
| func (e ErrNegativeSqrt) Error() string { |
| return fmt.Sprintf("Sqrt: negative number %g", e) |
| } |
| |
| const delta = 1e-10 |
| |
| func Sqrt(f float64) (float64, error) { |
| if f < 0 { |
| return 0, ErrNegativeSqrt(f) |
| } |
| z := f |
| for { |
| n := z - (z*z-f)/(2*z) |
| if math.Abs(n-z) < delta { |
| break |
| } |
| z = n |
| } |
| return z, nil |
| } |
| |
| func main() { |
| fmt.Println(Sqrt(2)) |
| fmt.Println(Sqrt(-2)) |
| } |
