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)

}