A Stock Control Policy for Important Spares in a Two Level Stores System

This paper describes the results of an investigation to determine correct re-order levels and order quantities. The problem had three important features:

1. i)
   a simple stock control system was required for about 15,000 items;
    
2. ii)
   run-out costs needed to be estimated;
    
3. iii)
   the solution required best stock levels and order quantities for a central store and for smaller stores supplied by it.
    

The problem arose because it was felt that production delays were being caused by the stores too frequently being unable to supply spares.Items were grouped by their importance and portability. Average run-out costs were estimated for each group. An approximate model of the two level stock holding problem was derived. An iterative process was required to obtain solutions.It was observed that the stock control rules were insensitive to run-out cost, and that items of equal run-out cost had widely differing run-out probabilities. This indicates that, in this case, it is invalid to group items by importance and to assign fixed run-out probabilities to each group.     

Forecasting and Stock Control for Intermittent Demands

Exponential smoothing is frequently used for the forecasts in stock control systems. The analysis given shows that intermittent demands almost always produce inappropriate stock levels. Demand for constant quantities at fixed intervals may generate stock levels of up to double the quantity really needed. A method of overcoming these difficulties is described, using separate estimates of the size of demand, and of the demand frequency. The rules for setting the safety stock levels have also to be adjusted before consistent protection can be obtained against being out of stock.     

一体化生产企业进货决策研究

综合考虑一体化生产企业原料使用中存在的间接消耗和循环消耗情况、企业进货受到的多种约束条件的限制以及多种物资的批量折扣的存在,在建立企业物资需求模型、进行物资需求量计算的基础上,建立了一体化生产企业进货决策模型,进而提出了模型的两种可供选用的求解方法：分解法、调整法。算例求解结果正确合理。     

ACD模型在沪市中的实证研究

在证券交易中,交易持续期反映了市场交易的重要信息,因此对交易者行为具有重要的影响,并且影响到证券市场的流动性.为了检验在交易中交易持续期对交易的影响,本文选择了沪市A股的四只股票,利用由Engle和Russell提出ACD模型对其交易持续期进行了实证研究,讨论了交易持续期的相关性质,表明交易持续期具有明显的日内模式,并检验log-WACD模型与中国证券市场的吻合程度.     

Stock Control of Manufacturing Parts — A Case Study

The approach adopted for stock control of manufacturing parts in a small company is described. In particular, material requirements planning is compared with the standard stock control method previously in use, and safety buffering is considered. By altering the company's stock-holding and ordering policies a significant saving is achieved.     

The Determination of the Optimum Joint Replenishment Policy for a Group of Discount-Connected Stock Lines

This paper investigates the situation where a joint replenishment order for a group of stock lines from a common supplier qualifies for a quantity discount provided the total order equals a specified number of units. It is assumed that, when any line in the group reaches its reorder point, an order of this size is made for the whole group and it is the problem of how to determine the optimum order "mix" which is considered here. In the case of a group consisting of two lines only, an analytical solution is derived which, assuming Poisson sales-rates, gives the individual stock levels for which the expected number of sales between successive replenishments is maximized for a given total stock. However, for groups of more than two lines, it was necessary to resort to numerical methods and a computer program is described which uses a quasi dynamic-programming approach to determine the optimum set of individual stocks for any given set of sales-rates and total stock. Based on the results from this program, a "ready reckoner" has been constructed which permits an easy look-up to obtain the optimum allocation of any given total stock between the lines of a group of any size and sales-rates. Finally, the possible extension of this approach to other multi-item inventory problems is discussed.     

Stock Control and the Undershoot of the Re-order Level

Practical stock-control systems are frequently based on a policy of reviewing the stock balance and placing an order if this has fallen to or below a set level R. In order to facilitate the calculation of the control parameters, the assumption is generally made that the stock balance is exactly R when an order is placed, whereas in practice it may have fallen below R. This paper uses a steady-state analysis to evaluate some relatively simple adjustments which may be incorporated to handle this undershoot.     

我国股市收益的双长记忆性检验——基于VaR估计的ARFIMA-HYGARcH-skt模型

针对股市收益分布的"尖峰肥尾"特征,引入了偏t分布作为新息分布。基于VaR方法,从风险估计的角度,利用ARFIMA(2,d_1,0)-HYGARCH(1,d_2,1)-skt模型对1996年12月17日至2007年7月5日期间的沪深股市收益进行了实证分析.实证结果显示:沪深股市具有显著的双长记忆特征;上海股市的日收益率和波动率的长记忆性均比深圳股市强;ARFIMA(2,d_1,0)- HYGARCH(1,d_2,1)-skt模型对我国股市收益具有较强的风险估计和预测能力。     

Stock Control—Experience and Usable Theory

Previous work on stock control has been mainly concerned with specific models or situations. This paper is an attempt at a more general method capable of dealing with distributed demands coupled with distributed lead times for a single stage stock system. Although primarily intended for manual operation, extensions to computer use are indicated. The criterion for determining stock investment is discussed and one based on return on capital employed is advocated.     

Application of Dynamic Programming to the Control of Stock and to the Calculation of a Maximum Stock Capacity

At the beginning the problem, as expressed by the heads of the Company which posed it, was in essence to find out whether, within the framework of a limited and well-defined expansion to level off in 1961, the existing capacity for stocks at a port used for shipping overseas would or would not be sufficient (it was thought it would not be).If more warehouses were shown to be needed, the amount of this extra capacity was to be worked out.It was very quickly discovered by an examination of the situation that the real problem would be rather to advise rules of stock management so as to take the best advantage of the existing stock capacity, in this way reducing the investment in buildings and maintenance to a minimum.Study of the model confirmed that the new management rules would make it unnecessary to increase the existing stock capacity.The model has the following characteristics: non-stationary process (e.g. an ever-changing situation), and an absence of any hypothesis on even the type of decision as to the method of renewing stock.Dynamic Programming used for this set of circumstances has made it possible to arrive at optimum management rules, demonstrating, incidentally, the power of this method in the study of non-stationary processes.     

侦测股市时间序列相关性的三种方法

运用方差方法.重标极差方法(R/S)和消除趋势波动分析方法(DFA)对美国股市标准普尔500指数的收盘价进行分析.结果表明:此股票市场指数具有状态持续性特征及自相似特征.同时兼具混沌等非线性特征.通过这三种方法对同一股市进行分析更能全方位的诠释相关性在股票市场理论应用的必要性及可行性,并且对股票市场理论建模.预测和管控策略的制定及实施具有重要意义.     

The Cutting Stock Problem in the Flat Glass Industry -- Selection of Stock Sizes

In the glass industry holding good stock sizes appears to have at least as big an impact on trim loss as cutting up the stock plates efficiently. In this paper two tech niques are described for determining "optimal" stock sizes, one a heuristic method and the other an integer programming algorithm. Several actual applications within the glass industry are described, and illustrative results of the improvements in wastage that have been achieved are given.     

A Simple Method of Production Planning in Multi-item Situations

The paper describes a simple method of stock control and scheduling of the production of many items due originally to Spencer. Two case studies are presented in which the basic ideas of this method are used to adjust smoothed production plans to meet capacity or raw material availabilities.     

股灾背景下中美股市风险溢出的结构转换研究

选取中美股票市场的上证综指、恒生指数和标普500指数作为研究对象进行风险溢出效应研究,结果表明,总体而言上海市场与香港市场之间双向风险溢出效应最为显著,香港市场和美国市场次之,而上海市场与美国市场之间的双向风险溢出效应最不显著;从风险溢出方向与强度方面分析,无论牛熊市,香港市场对上海市场在极端风险时刻的风险溢出要显著强于上海市场对香港市场的溢出,而香港市场与美国市场之间在牛市行情下双向风险溢出效应相对均衡,在熊市行情下香港对美国的风险溢出相对更大,与常理不一致的结果是上海市场在牛市期间对香港市场的风险溢出效应要大于熊市,围绕这一点进一步采用Chi-plot相关图进行分析表明中国市场还未达到“中国打喷嚏,世界经济感冒”的状态;从风险溢出效应的动态趋势分析看出两个牛市阶段各市场的风险溢出呈现不同特征。美国市场对中国市场的风险溢出效应总体平稳,而中国市场对美国市场的风险溢出效应存在一定差异,在低分位数水平相差较大,随分位数水平提高两个牛市阶段的风险溢出趋于一致。但上海市场对香港市场的风险溢出随时间变化在牛市阶段逐步增强,而香港市场对上海市场的风险溢出则逐渐下降。     

考虑生产计划的多周期切割问题优化研究

切割生产广泛存在于工业企业,是原材料加工的重要环节。已有文献主要关注单周期切割问题,但是切割计划也是生产计划的一部分,切割计划和生产计划应该协调优化,达到全局最优。本文研究考虑生产计划的多周期切割问题,目标是最小化运营成本,包括准备成本、切割成本、库存成本以及母材消耗成本。首先建立混合整数规划模型;提出动态规划启发式算法;最后对算例在多种情境下测试,分析成本因子变化对最优结果的影响。算法结果与CPLEX最优结果比较,平均误差为1.85%,表明算法是有效的。     

基于GA-RS-LR算法的公司财务与个股投资探究

运用遗传算法-粗糙集-逻辑回归方法(GA-RS-LR)探讨我国A股上市公司财务与股票收益的关系.运用GA-RS方法获得财务指标最优约简;运用LR模型探求两者关系.最终,经GA-RS约简,60个财务指标中有17个对股票投资有重要影响;通过LR模型,4个指标具有显著效应;其中,负债与权益市价比为5.82%负效应,其余为正效应.对2015年股票相对波动进行预测得到70%的准确率,验证了GARS-LR模型对中长期投资的有效性.     

The Effect of Estimation Risk in Establishing Safety Stock Levels in an Inventory Model

This article illustrates the impact of estimation risk on decisions involving a one-period inventory problem such as the Christmas-tree stocking problem. It is shown that when estimation risk is ignored, stock levels may be incorrectly compiled and service levels may be inadequate. This article describes a regression-based method which adjusts the size of the stock by incorporating an additional safety stock requirement which reflects the uncertainty associated with lack of precise knowledge of the true parameters.     

流动性风险与股票收益率

文运用两阶段回归方法,利用上海证券交易所和深圳证券交易所的A股交易数据,针对流动性风险与股票收益率之间的关系进行了实证检验。在把流动性风险分解成系统流动性风险和个体流动性风险以后,作者发现无论是系统流动性风险还是个体流动性风险都对股票收益率有显著的影响;并且与成熟市场不同的是,在中国市场上个体流动性风险对收益率的影响比系统流动性风险的影响要更显著。因此在今后研究中国股市的流动性定价时,研究人员需要考虑个体流动性风险才能够对股票收益率进行更好的解释。     

Safety Stock Determination with Serially Correlated Demand in a Periodic-Review Inventory System

We consider a periodic-review inventory replenishment model with an order-up-to-R operating doctrine for the case of deterministic lead times and a covariance-stationary stochastic demand process. A method is derived for setting the inventory safety stock to achieve an exact desired stockout probability when the autocovariance function for Gaussian demand is known. Because the method does not require that parametric time-series models be fit to the data, it is easily implemented in practice. Moreover, the method is shown to be asymptotically valid when the autocovariance function of demand is estimated from historical data. The effects on the stockout rate of various levels of autocorrelated demand are demonstrated for situations in which autocorrelation in demand goes undetected or is ignored by the inventory manager. Similarly, the changes to the required level of safety stock are demonstrated for varying levels of autocorrelation.     

Stock Control Using the Stock Level Frequency Distribution

Stock level frequency distributions are derived for continuous review stock control policies in which the lead time demand is normally distributed. The percentage points of the distributions have been tabulated, and the table can be used to determine the reorder point that will meet a specified customer order quantity from stock with a specified probability. The results can also be used to determine the order up to point for a periodic review policy and the reorder point for a mixed policy.