How to generate the cumulative variable from existing variable in vensim?

[Susan@6]

I wanted to generate a new variable, which is a cumulative frequency on another variable in the model. Eg:

Year GDP Cumulative GDP
2014 100
2015 200 300
2016 300 600

Now, how do we find this Cumulative GDP? I have Vensim PLE only.

[tomfid]

Accumulation implies a stock, so you could create a stock of Cumulative GDP with an inflow of Current GDP. Note that this implies a change of units (if the flow is $/year, and the stock is $ for example).