An important contribution in this field is represented by [25], where the authors define a linear mathematical model to
formulate PAP, taking into account some important operative constraints. In particular, they guarantee that each product type
is concentrated in a specific stocking zone in order to simplify the inventory management and the equipments utilization.
The authors also assume that the quantity to be stocked and the capacity required by each product type are known information.
The problem is modeled with reference to a specific warehouse layout, depicted in Fig. 1. After considering different
warehouse management strategies, the authors conclude that if a product has to be allocated in a set of different slots, then it
is better to assign it firstly in adjacent positions; secondly, in opposite positions; third, in posterior positions; then, in generic
positions. Thus, some assignment priorities have been defined. The goal of the model is to find the best products allocation
strategy, minimizing the sum of the penalties, that depend on the product-slot assignment, and handling costs.
The complexity of the model increases with the number of the handled products classes and slots. For this reason, in some
real cases, it is not practicable to apply an exact algorithm for solving the problem; thus, the authors also propose a branch
and bound based heuristic.