How to take a cube root in Go?
Have you tried myCubicRootOfx = Pow(x, 1.0/3)
?
edited: thanks to Jason McCreary
comment:
We cannot use 1/3
as the 2nd parameter to Pow
as this is a integer division and hence doesn't produce the expected 1/3 value. By using 1.0/3
or 1/3.0
etc. we effectively produce a float with the 0.333333... value.
I wrote the cube root function using Newton's method as part of the Go Tour Exercise 47. Perhaps the two functions below (Cbrt1
and Cbrt
) are helpful.
package main
import (
"fmt"
"math/cmplx"
)
// Newton's method cube root function that hopes for
// convergence within 20 iterations
func Cbrt1(x complex128) complex128 {
var z complex128 = x
for i:= 0; i < 20; i++ {
z = z - ((z*z*z - x) / (3.0*z*z))
}
return z
}
// Newton's method cube root function that runs until stable
func Cbrt(x complex128) complex128 {
var z, z0 complex128 = x, x
for {
z = z - ((z*z*z - x) / (3.0*z*z))
if cmplx.Abs(z - z0) < 1e-10 {
break
}
z0 = z
}
return z
}
func main() {
fmt.Println(Cbrt(2.0) , "should match" , cmplx.Pow(2, 1.0/3.0))
}
As you're using Newton's method, I suppose you're starting with a positive real number.
So you don't need complex numbers.
You may simply do
package main
import (
"fmt"
"math"
)
func main() {
x := 100.0
root := math.Pow(x, 1.0/3.0)
fmt.Println(root)
}