全球化趨勢下一般企業經常面對的問題. 高度需求變動 訂貨前置時間長 不可靠的供應程序 大量的儲存單位 (SKUs). 案例. 三＊工業的問題 …( 前置時間 ) 手機的產品壽命週期： 20000 0 元 ( 產品壽週期需求變異 ) Ipad 對電子書的衝擊 … ( 競爭需求變異 ) 新機推出後一個月 — IPhone 跌 2 千； hTC 跌 5 千；三星跌 3 千 … 智慧型手機可能帶來衝擊 … 電子書 遊戲機 隨身聽 衛星導航 …. Why Is Inventory Important? 1.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Distribution and inventory (logistics) costs are quitesubstantial
Total U.S. Manufacturing Inventories ($m):
InventorySales Ratio (U.S. Manufacturers):
Note:
• No Stockouts
• Order when no inventory
• Order Size determines policy
Inventory
Order
Size
Avg. Inven
Time
Cycle Time =T
(the time that elapses between the placement of an order and its receipt)
Total inventory cost relatively insensitive to order quantities
Actual order quantity: Q
Q is a multiple bof the optimal order quantity Q*.
For a given b, the quantity ordered is Q = bQ*
Short lifecycle products(例如，ipad…)
Example – Swimsuit production
Example – Swimsuit production
Example – Swimsuit production
Example – Swimsuit production
FIGURE 26: Average profit as a function of production quantity
Selling Price  Variable Ordering (or, Production) Cost
Variable Ordering (or, Production) Cost  Salvage Value
=> optimal production quantity < average demand.
Example – Swimsuit production
Example – Swimsuit production
225000
FIGURE 28: Profit and the impact of initial inventory
Example – Swimsuit production
225,000 (from the figure) + 5,000 x 80 = 625,000 (125 5000=625000)
371,000 (from the figure) + 5,000 80 = 771,000
Example – Swimsuit production
Let X is the tradeoff point
Example – Swimsuit production
(s, S) policy or (min, max) policy
REASONS
where z is chosen from statistical tables to ensure that the probability of stockouts during leadtime is100%SL.
z is chosen from statistical tables to ensure
that the probability of stockouts during lead time is exactly 1  α
FIGURE 29: Inventory level as a function of time in a (Q,R) policy
Inventory level before receiving an order =
Inventory level after receiving an order =
Average Inventory =
Average monthly demand = 191.17
Standard deviation of monthly demand = 66.53
Average weekly demand = Average Monthly Demand/4.3 =44.58
Standard deviation of weekly demand = Monthly standard deviation/√4.3=32.08
Weekly holding cost =
Optimal order quantity =
Average inventory level = 679/2 + 86.20 = 426
r = length of the review period
L = lead time
AVG = average daily demand
STD = standard deviation of this daily demand.
(basestock level)
(訂購量=保護期間的預期需求+安全存量再訂購點時的現有數量)
FIGURE 210: Inventory level as a function of time in a periodic review policy
FIGURE 211: Service level inventory versus inventory level as a function of lead time
FIGURE 212: Service level optimization by SKU
Warehouse One
Supplier
Warehouse Two
Market Two
Market One
Warehouse
Supplier
Market Two
Risk Pooling ― Question1FIGURE 213: A serial supply chain
FIGURE 214: The warehouse echelon inventory
The reorder point of warehouseis
Where
Le=echelon lead time, defined as the lead time between the retailers and the warehouseplusthe lead time between the warehouse and its supplier
AVG=average demandacross all retailers
STD=standard deviation of demand across all retailers
FOCUS: not reducing costsbut reducing inventory levels. (JIT)
Significant effort in industry to increase inventory turnover
嗯, 請給我一分鐘想想.... 上週我們已銷售250個輪胎.... 所以下週我們將要銷售....
Ft = Ft1 + (Dt1  Ft1)
=Dt1 +(1 )Ft1
Ft：第t期的預測需求
Dt：第t期的實際需求
α：平滑係數
Suppose the projected demand for year 3 is 1320 units.
quarter
quarter
quarter
quarter
TM 12.3b
Actual
forecast
MAD
=
n
]
[
Actualt
forecastt
2
100%
(
Actual
forecast)
MSE
=
Actualt
MAPE
=
n

1
n
平均絕對誤差、均方誤差與平均絕對百分比誤差平均絕對誤差、均方誤差與平均絕對百分比誤差