Normally, the transportation model is used to solve problems involving several physical sources of product and several physical uses of the product, as in factories and warehouses

How is it possible to use the transportation model where the "routes" are from one time period to another? Describe how this provides aggregate planners with a usable mathematical model.

Time travel is not involved. "From" regular time March "To" demand May simply describes when production took place to provide the units sold in May. "From" April production "To" March demand simply describes back orders — demand in one month is met by production in a later period. The algorithm is optimizing — it minimizes cost over the planning period; the algorithm balances supply and demand by combinations of capacity options and demand options.