tour-go-exercise-56.go

package main

import (
    "fmt"
    "math"
)

type ErrNegativeSqrt struct {
	number float64
}

func (e ErrNegativeSqrt) Error() string {
    return fmt.Sprintf("can't square root of negative number: %.f", e.number)
}

func Sqrt(x float64) (float64, error) {
    if x < 0 {
        return x, ErrNegativeSqrt{x}
    }
    
    z := 1.0
    old_z := 0.0
    delta := 0.2
    
    for {
        old_z = z
        z = z - ((math.Pow(z, 2) - x) / (2 * z))
 
        delta_newton := math.Abs(z - math.Sqrt(x))
 
        if delta_newton <= delta || old_z == z {
            return z, nil
        }
    }
}

func main() {
    fmt.Println(Sqrt(2))
    fmt.Println(Sqrt(-2))
}