func main() {
    var test []Pow
    var x1 Pow
    x1.distance = 110
    x1.grade = 0.31
    var x2 Pow
    x2.distance = 80
    x2.grade = 0.25
    var x3 Pow
    x3.distance = 120
    x3.grade = 0.18
    var x4 Pow
    x4.distance = 70
    x4.grade = 0.21

    test = append(test, x1)
    test = append(test, x2)
    test 
 
= append(test, x3)
    test = append(test, x4)
    var distance_sum float64
    var powList []Pow
    grade:= float64(0)
    for _,v := range test{
        var temp Pow
        distance_sum+=1/math.Pow(v.distance,2)
        temp.distance = 1/math.Pow(v.distance,2)
        temp.grade = v.grade
        powList 
 
= append(powList, temp)
    }
    for _,v1:=range powList{
        grade+=v1.grade*(v1.distance/distance_sum)
    }
    beego.Debug(grade)
}