NOTE: Subscripts are only supported in Vensim Professional and DSS only. Models with subscripts can be used with the Vensim Model Reader.
A Subscript allows one variable and equation to represent a number of different distinct concepts. For example consider the equation:
profit = revenue - cost
If we are modeling a chain store we might be interested in activities at each store. Thus we could define store as a Subscript
store : WAYLAND, HARVARD, LONGMEADOW, OLALLA, OAK RIDGE, LAS VEGAS
Each name describes a different store (in this case by location). Now we can write the equation
profit[store] = revenue[store] - cost[store]
This equation says that for each store, profit specific to that store is computed by taking revenue specific to that store and subtracting cost specific to that store. Thus instead of writing six equations, you need only write one. In addition, if you add another store, you do not need to rewrite the equation.
Variables in a model may have different Subscripts, or no Subscripts. For example, we might have:
corporate profit = SUM(profit[store!]) - corporate overhead
This equation adds up profit across all stores and then subtracts corporate overhead. The point here is that you can mix and match subscripts and regular variables, and this usually turns out to be necessary.