Go tour sqrt VS newton's method: http://tour.golang.org

Loops and Functions Go Tour Exercise

package main

import (
    "fmt"
    "math"
)

func Newt(x float64) float64 {
    if x == 0 { return 0 }
    z := 1.0
    for i := 0; i < int(x); i++ {
        z = z - ((math.Pow(z, 2) - x) / (2 * z))
    }
    return z
}

func Sqrt(x float64) float64 {
    return math.Sqrt(x)
}

func main() {
    times := 15
    for i := 0; i < times; i++ {
        sqrt := Sqrt(float64(i))
        newt := Newt(float64(i))
        fmt.Println(i, "squared:")
        fmt.Println("  Sqrt:", sqrt)
        fmt.Println("  Newt:", newt)
        fmt.Println("  Difference:", math.Abs(sqrt-newt))
    }
}

If I may, you should replace math.Pow(z, 2) with z*z because math.Pow in this case is 100 times slower than the simple mult operation.

This test:

func BenchmarkMathPow(b *testing.B) {
	var f float64
	for i := 0; i < b.N; i++ {
		f = math.Pow(123456, 2)
	}
	s := fmt.Sprint(f)
	s = fmt.Sprint(s)
}

func BenchmarkSquared(b *testing.B) {
	var f float64
	for i := 0; i < b.N; i++ {
		f = 123456 * 123456
	}
	s := fmt.Sprint(f)
	s = fmt.Sprint(s)
}

returns this result:

goos: linux
goarch: amd64
pkg: github.com/lhauspie/some-tests/perf
BenchmarkMathPow-8   	50000000	         30.9 ns/op	       0 B/op	       0 allocs/op
BenchmarkSquared-8   	2000000000	         0.29 ns/op	       0 B/op	       0 allocs/op
ok  	github.com/lhauspie/some-tests/perf	2.678s
Success: Benchmarks passed.