A Hierarchical Approach to Production Planning.

Abstract : We begin this discussion with an analysis of the hierarchical framework discussed in Hax and Meal, 1975. After defining the different levels of the hierarchy we provide necessary and detailed models. Several interpretations and consequences of these results are discussed. In addition, it is shown that planning horizons to insure consistency on a detailed level are intimately related to planning on an aggregate level. Although we cannot demonstrate the optimality of the approach of Hax and Meal, lower bounds are easily derived. For the remainder of the report, we do not consider the aggregate product structure of Hax and Meal. Instead, in a linear model, we aggregate all items together. Under a quite general cost structure, we are able to characterize optimal aggregate production which can be optimally disaggregated. The analysis is extended from the single to the multi-echelon case. We formalize some of the preceding notions and present a more general underlying theory. The aggregate characterization is closely related to properties of Leontief systems. In addition, a new characterization of Leontief Substitution Systems is presented. Finally, we extend the original problem to include both regular and overtime considerations and then fixed charges in production. (Author)