constructing cumulating variable

[John Ted]

Hello All, My Name is John Tedd.

I want to construct a variable like Xijt=Xij1960+Xijt[-n-1]. Xijt is labor productivity and the time period is from 1960-2010, for country i, sector j and year t. The point is that I have to have labor productivity in 1960 first. Then I want to use that a base and calculate for the rest. For example Xij1961=Xij1960+ Zijt (another variables). Xij1962=Xij1961+Zijt, Xij1963=Xij1962+Zijt etc

Can you help me how to write a code that can work like this?

Thanks

[Carlo Lazzaro]

John:
welcome to the list.
Is what you're after is a running sum, see -help sum()-.