go-tour exercise1: implement the square root function using Newton's method

go_tour_ex1_sqrt.go

package main

import (
    "fmt"
    "math"
)

const Delta = float64(1e-15)

func Sqrt(x float64) float64 {
    z := float64(1)
    for {
        d := (z*z - x)/z/2
        if math.Abs(d) < Delta {
            break
        } else {
            z -= d
            //fmt.Println(z)
        }
    }
    return z
}

func main() {
    fmt.Println(Sqrt(4))
    fmt.Println(math.Sqrt(3))
}

go_tour_ex1_sqrt_named_result.go

package main

import (
    "fmt"
    "math"
)

const Delta = float64(1e-15)

func Sqrt(x float64) (z float64) {
    z = float64(1)
    for {
        d := (z*z - x)/z/2
        if math.Abs(d) < Delta {
            break
        } else {
            z -= d
        }
    }
    return
}

func main() {
    fmt.Println(Sqrt(3))
    fmt.Println(math.Sqrt(3))
}

go_tour_ex_sqrt_err.go

package main

import (
    "fmt"
    "math"
)

const Delta = float64(1e-15)

type ErrNegativeSqrt float64

func (e ErrNegativeSqrt) Error() string {
    // here needs to convert e (float64(e)) first;
    // otherwise, it will go to an infinite loop, causing out of memory
    return fmt.Sprint("cannot Sqrt negative number:", float64(e))
}

func Sqrt(x float64) (float64, error) {
    var (
        err error
        z float64
        )

    if x < 0 {
        err = ErrNegativeSqrt(x)
    } else {
        z = float64(1)
        for {
            if d := (z*z - x)/z/2; math.Abs(d) < Delta {
                break
            } else {
                z -= d
            }
        }
    }
    return z, err
}

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