经济决策定量方法第三章课件.ppt

1 1 Chapter3 Inventory Models ★ deterministic model ★ stochastic model Inventory Models The study of inventory models is concerned with two basic questions: How much should be ordered each time When should the reordering occur The objective is to minimize total variable cost over a specified time period (assumed to be annual in the following review). Inventory Costs Ordering cost -- salaries and expenses of processing an order, regardless of the order quantity Holding cost -- usually a percentage of the value of the item assessed for keeping an item in inventory (including finance costs, insurance, security costs, taxes, warehouse overhead, and other related variable expenses) Backorder cost -- costs associated with being out of stock when an item is demanded (including lost goodwill) Purchase cost -- the actual price of the items Other costs Deterministic Models The simplest inventory models assume demand and the other parameters of the problem to be deterministic and constant. The deterministic models covered in this chapter are: Economic order quantity (EOQ) Economic production lot size EOQ with planned shortages EOQ with quantity discounts Economic Order Quantity (EOQ) The most basic of the deterministic inventory models is the economic order quantity (EOQ). The variable costs in this model are annual holding cost and annual ordering cost. For the EOQ, annual holding and ordering costs are equal. Deterministic Model Economic Order Quantity Assumptions A : Annual number of items demanded, c : Unit cost of procuring an item, T : Time between orders, h : Annual cost per dollar value of holding items in inventory. K：fixed cost per order The order quantity (Q) to replenish inventory arrives all at once just when desired, namely, when the inventory level drops to 0. Planned shortages are not allowed Economic Order Quantity Deterministic Model Deterministic Model Deterministic Model Deterministic Model Deterministic Model When the unit holding