How to put a function on QlikView?

[#1]

I currently conducting a barycentric function weighting the data based on a user selected date. I also start making a centroid function but I do not know how I can integrate QlikView and how to handle data with QlikView my function?

[#2]

Please translate to english

[#3]

If the function is simple, then create a user defined function with parameters.

LET vMultiplication = $1+$2 ;

$(vMultiplication(3, 4))

The above is not possible, please use Macros