Fyralagersmodell

Fyralagersmodell, often translated as the four-warehouse model, is a conceptual framework used in inventory management and supply chain planning to study distribution problems across four facilities. The model abstracts stockholding and movement of goods among four warehouses and to end customers, enabling analysis of how different cost components and constraints influence distribution choices.

Typically, each warehouse can hold stock, trigger replenishments, and transfer goods to other warehouses or directly to customers. The decision variables include inventory levels at each warehouse, quantities shipped between warehouses, and quantities delivered to customers, all across one or more time periods. The model accounts for demand at customer locations, capacity limits, lead times, and possibly service-level requirements.

The objective is usually to minimize total cost, comprising purchasing or production costs, inventory holding costs, transportation and inter-warehouse transfer costs, and fixed ordering or setup costs, while satisfying demand and respecting capacities. The model can also be formulated to maximize service level or minimize total cost under backorder or stockout allowances.

From a mathematical perspective, the fyralagersmodell can be formulated as a linear programming or mixed-integer programming problem, or as a multi-period network flow problem. It typically involves decision variables for initial stock, replenishment quantities, inter-warehouse transfers, and customer shipments, subject to demand balance constraints, warehouse capacity constraints, and nonnegativity restrictions.

Applications include strategic network design, routine distribution planning, and multi-echelon inventory management, particularly in networks with four facilities or when studying the effects of adding or removing a warehouse. Variants may extend the number of facilities, incorporate stochastic demand, or integrate production, routing, and scheduling decisions.