I want to do a temporal decomposition using STATA. Assume the following data below where x= y*z
year x y z
2015 8 4 2
2016 12 3 4
2017 16 4 4
It is not necessary to show the entire decomposition but a crucial step is calculating the changes in the variables:
year x y z delta x delta y delta
2015 8 4 2
2016 12 3 4 4 -1 2
2017 16 4 4 4 1 0
But this involves subtracting one row from the previous row . However, nearly all the STATA functions refer to expression within a row. How can I create a loop which calculates and generates the variables delta x,y,z?

Thanks!

Rutger