In general, a transshipment model allows shipments between any pair of origin (plant) i and transshipment node j (wholesaler), and between any pair of transshipment node j and destination (retailer) k. In the MB distribution case, however. each of the four beer plants is designated to a limited and diflerent group different wholesalers as authorized transshipment nodes, and similarly each of the seven wholesalers is responsible for a limited and different group of retailers as authorized destinations. In this sense, the MB distribution system is a special transship ment problem. For the sake of exposition, let us consider a generalized versim d MB distribution system, namely, removing the limits of designated groups such that it presents a standard transshipment problem with four origins, seven transshipment nodes, and ten destinations. The transportation costs in Tables 6.1 d 6.2 are also modified in Tables 6.8 and 6.9, respectively.
compared with original cost data in Table 6.1, now there are no infeasible routes (i.e., forbidden cells "-") for the plant-wholesaler transpiration- For convenience, we introduce the following decision variables for origin transshipment transportation: