package main
 
import (
    "fmt"
    "errors"
    "math"
)
 
func Cosine(a []float64, b []float64) (cosine float64, err error) {
    count := 0
    length_a := len(a)
    length_b := len(b)
    if length_a > length_b {
        count = length_a
    } else {
        count = length_b
    }
    sumA := 0.0
    s1 := 0.0
    s2 := 0.0
    for k := 0; k < count; k++ {
        if k >= length_a {
            s2 += math.Pow(b[k], 2)
            continue
        }
        if k >= length_b {
            s1 += math.Pow(a[k], 2)
            continue
        }
        sumA += a[k] * b[k]
        s1 += math.Pow(a[k], 2)
        s2 += math.Pow(b[k], 2)
    }
    if s1 == 0 || s2 == 0 {
        return 0.0, errors.New("Vectors should not be null (all zeros)")
    }
    return sumA / (math.Sqrt(s1) * math.Sqrt(s2)), nil
}
 
func main(){
    cos, err := Cosine([]float64{0, 1, 0, 1, 1}, []float64{1, 0, 1, 0, 0})
    if err != nil {
        panic(err)
    }
    fmt.Println(cos)
}

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