SIG1.go

package main

import (
	"fmt"
	"math"
)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
	return fmt.Sprintf("cannot Sqrt negative number %f", e)
}

func Sqrt(x float64) (float64, error) {
	z := float64(100)
	if x >= 0 {
		count := 0
		realSqrt := math.Sqrt(x)
		for math.Abs(realSqrt-z) >= 1e-9 {
			z = z - (z*z-x)/(2*z)
			count++
			fmt.Println("Z[", count, "] =", z)
		}
		fmt.Println("Used", count, "time(s) to reach sqrt(x)")
		return z, nil
	}
	return z, ErrNegativeSqrt(x)
}

func main() {
	fmt.Println(Sqrt(-5))
}