日益增長的國際需求將近期內市場價格 推到一個未知水準，當然來是隨機的。採購已被認定為全球競爭市場中主要能力，許多公司人員面對許多挑戰，其中最大的一項就是如何在原物料市場價格不確定狀況下依然能滿足廠內原物料的需求。採購市場中價格支付狀況會高度影響總成本，所以面對不確定價格的狀況下，何時該購買是一項重要決策。
如今， 原物料價格占採購總成本的比例越來高決 策的複雜性在於策者必須 判斷未來價格將上漲或下跌，因此對於決策者說已有的庫存量和一期市場價格訊息可以幫助判斷。除此之 外， 這篇文章加入了先期指標的概念幫助決 策者定適當的採購量。 依據先期指標的資訊來幫助我們預測價格趨勢，在 指標顯示下跌 時，等待機會購買；在價格顯示上漲透過分散訂避開高市場的風險。

Growing international demand increasing recently pushed prices to unknown level. Naturally,the future market prices are stochastic. Procurement has been identified as a main ability to compete in the global marketplace in a manufacture's. Many procurement staff confronts one of the greatest challenges which are how to match the demand in the factory when material cost is always uncertainty. Price paid in procurement markets can highly influence the total cost.The decision to be made is facing fluctuating market price at which price to purchase.
Nowadays, raw material price are responsible for an increasing portion of total procurement cost. One of the complexities that decision-maker must deal with is to judge the price increase or decrease in the future. Therefore, for decision-maker, the information of the inventory in previous period and the real market price can help them to determine the appropriate lot size in each period.We are going to take leading indicator into account and provide an ordering policy to fit different situations. According to leading indicator, help us predict the price trend.When the leading indicator show that the price might go down in near future, we would keep remained inventory or ordering little quantities to wait a better market price to purchase more; or, when the leading indicator show the price might go up in near future, we would purchase at low spot price or discrete order quantity to avoid the risk of price.

[1] Harvey M. Wagner and Thomson M. Whitin, “Dynamic version of the economic lot size model”, Management Science, Vol 5, No. 1, pp. 89-96, October 1958.
[2] Fabian, T., et al., "Purchasing raw material on a fluctuating market", Operations Research, Vol.7, No.1, pp. 107-122, February 1959.
[3] B. Lev and A. L. Soyster, “An Inventory Model with Finite Horizon and Price Changes”, Vol. 30, No.1 , pp.43-53, January 1979.
[4] Benjamin Lev and Howard J. Weiss,“Inventory models with cost changes”, Operations Research, Vol 38, No.1 , pp. 53-63, February 1990.
[5] Horacio Hideki Yanasse, “EOQ systems: The case of an increase in purchase cost”,Operational Research Society, Vol 41, No. 7, pp.633-637, January 1990.
[6] Hariga, Moncer A., "Economic analysis of dynamic inventory models with non-stationary costs and demand", International Journal of Production Economics, Vol.36, No.3, pp. 255-266, October 1994.
[7] James Flynn and Stanley Garstka, “The Optimal Review Period in a Dynamic Inventory Model”,Operations Research, Vol. 45, No. 5, pp. 736-750, October 1997.
[8] Stef van Buuren,“Fitting arma time series by structural equation models”, Psychometrika, Vol 62, No.2, pp. 215-236, June 1997.
[9] James C. Benneyan, “Statistical Quality Control Methods in Infection Control and Hospital Epidemiology, Part II:Chart Use, Statistical Properties, and Research Issues”, Vol. 19, No. 4, pp.265-283, April 1998
[10] Martel, Alain, and Andre Gascon., "Dynamic lot-sizing with price changes and price-dependent holding costs", European Journal of Operational Research, Vol.111, No.1, pp. 114-128, November 1998.
[11] Gurnani, Haresh, and Christopher S. Tang., "Note: Optimal ordering decisions with uncertain cost and demand forecast updating", Management science, Vol. 45, No.10, pp. 1456-1462, October 1999.
[12] Montgomery, DQUGLAS C., and W. H. Woodall, “Research Issues and Ideas in Statistical Process Control”, Journal of Quality Technology, Vol. 31, No. 4, October 1999.
[13] Mary J. Meixell and S. David Wu, “Predicting the probability of a recession with nonlinear autoregressive leading-indicator models”, IEEE Transactions on semicondustor manufacturing, Vol. 14, No. 1, February 2001
[14] Boyd, Stephen P., and LievenVandenberghe, “Convex optimization.” Cambridge university press, United Kingdom, 2004.
[15] Jamali, Abdul Sattar, and Li Jinlin. (2006), "False alarm rates for the Shewhart control chart with interpretation rules", WSEAS Transactions on Information Science and Applications,Vol. 3, No. 7, pp.238-241, April 2006.
[16] Jan Arnold, et al., “Raw material procurement with fluctuating prices”, International Journal of Production Economics, Vol.121, No. 2, pp. 353-364, October 2009.
[17] ”Research on the strategy of construction material procurement when the price fluctuation is considered”, Management and Service Science (MASS), 2010 International Conference on. IEEE, pp. 1-4, 2010.
[18] Chung-Yuan Dye and Tsu-Pang Hsieh,”Deterministic ordering policy with price- and stock-dependent demand under fluctuating cost and limited capacity”,Expert Systems with Applications, Vol. 38, No. 12, pp. 14976-14983, December 2011