OPTIMAL SAFETY-STOCK INVESTMENT THROUGH SUBJECTIVE EVALUATION OF STOCKOUT COSTS

This paper solves the problem of setting safety stocks by combining a subjective evaluation of the stockout-cost function with the usual holding-cost function. The technique given in this paper for estimating a decision maker's (DM's) disvalue function for stockouts is robust in terms of the shapes permissible for this function and allows for uncertainty on the part of the DM in expressing his/her trade-offs. The estimation technique could be applied to situations other than the safety-stock problem. We provide an optimization routine for the safety-stock problem which is designed to operate in conjunction with the estimation technique. Safety-stock levels are arrived at iteratively.     

Solving the Economic Lot-Scheduling Problem Using the Method of Prime Subperiods

In recent years the reported successes of Japanese production systems, particularly the just-in-time approach to inventory control, has caused managers to focus more of their attention on efficient decision-making procedures for determining production schedules that minimize inventory costs. One such potential area of attention is the economic lot-scheduling problem (ELSP), which occurs in a variety of manufacturing environments where machining operations are prevalent. The economic lot-scheduling problem addresses the determination of lot sizes for N products with constant demand (and cycled through one machine with a given production rate) to minimize setup and inventory costs. The most successful solution approaches to the ELSP have been based on the concept of a basic period that is of sufficient length for the production of all items, even though each item might not be produced during each repetition of the basic period. This paper proposes a heuristic approach to the solution of the ELSP (referred to as the method of prime subperiods), which is an extension of the basic period approaches. The procedure is described and demonstrated via an example and then tested using a set of six example problems previously employed in the literature related to the ELSP. The results indicate as good or superior performance by the proposed method of prime subperiods.     

The Airline Discount Fare Allocation Problem

This paper describes a useful extension of the well-known, single-period inventory or newsboy problem. Given a fixed number of identical seats available on a scheduled airline flight, what percentage should be offered for early sale at a predetermined discount fare and what percentage reserved for later sale at a higher full fare? This two-tiered pricing strategy with early discount pricing might be appropriate in any situation in which the price sensitivity of the inventoried items decreases as the end of the period approaches. Similar to the newsboy problem solution, the decision rule that maximizes expected profit is expressed as a simple function of the percentage difference in the two fares and two carefully defined probabilities.     

A Comparative Analysis of the Relative Effectiveness of Four Dynamic Lot-Sizing Techniques on Return on Investment

The relative performance of dynamic lot-sizing techniques has been of considerable interest to researchers in recent years. While research has addressed performance in terms of cost-effectiveness, researchers have not determined the impact of dynamic lot-sizing techniques on return on investment (ROI) as it applies to finished goods' schedules. The purpose of this research is to explore the relative performance of four dynamic lot-sizing techniques with regard to ROI, namely the Wagner-Whitin, Incremental Part Period, Silver-Meal, and Groff techniques. Computer graphics are employed to analyze the relative ROI effectiveness.     

Inventory Control and Scheduling of Multiple Products in a Common Facility*

Consider a set of chemical products to be produced in a single facility. Each product has its own unique reaction time (which is assumed to be independent of its batch size), as well as other cost and demand values. In this paper, we address the problem of determining the optimal number of batches, batch sizes, and an accompanying production schedule for these products in the single facility that will minimize the total cost. Two different algorithms have been developed for this problem, the performances of which are contrasted with classical cyclic production schedules. Finally, some guidelines for the application of these methods to real-life problems are outlined.     

On a stochastic process with a heavy-tailed distributed component describing inventory model type of (s,S)

In the present study, the stochastic process X(t) describing inventory model type of (s, S) with a heavy-tailed distributed demands is considered. The asymptotic expansions at sufficiently large values of parameter β = S ? s for the ergodic distribution and nth-order moment of the process X(t) based on the main results of the studies Teugels (1968 Teugels, J.L. (1968). Renewal theorems when the first or the second moment is infinite. Ann. Math. Stat. 39(4):1210–1219.[Crossref] , [Google Scholar]) and Geluk and Frenk (2011 Geluk, J.L., Frenk, J.B.G. (2011). Renewal theory for random variables with a heavy tailed distribution and finite variance. Stat. Probab. Lett. 81:77–82.[Crossref], [Web of Science ®] , [Google Scholar]) are obtained.     

“A JOINT ECONOMIC-LOT-SIZE MODEL FOR PURCHASER AND VENDOR”: A COMMENT*

Banerjee [1] developed a joint economic-lot-size model for the case where a vendor produces to order for a purchaser on a lot-for-lot basis under deterministic conditions. The assumption of lot-for-lot bases is restrictive in nature. In this note, a more general joint economic-lot-size model is suggested and it is shown to provide a lower or equal joint total relevant cost as compared to the model of Banerjee.     

An Empirical Study of Inbound Consolidation Opportunities

The current deregulated transportation environment has fostered wider freight rate differentials based on shipping weight. As a result, grouping inventory items for the purpose of consolidating inbound replenishment orders can be cost-effective. The pressure in some industries for just-in-time delivery of small lots has also created new opportunities for consolidation of orders. The objective of this research is to identify inventory-transport conditions where a consolidation strategy has cost-reduction potential. Logistics cost generated by ordering an ensemble of items consolidated into groups is compared to those generated by two independent, item reorder strategies. Using data from 150 ensembles, the cost-reduction potential of consolidating was correlated with characteristics of the individual inventory items in an ensemble, a dominant group of items in the ensemble, and the ensemble itself. Finally, response functions were derived and used to test the external validity of the results. For this purpose we used 25 randomly selected inventory ensembles obtained from a retail merchandising firm.     

REORDER-POINT MODELS WITH DISCRETE PROBABILITY DISTRIBUTIONS

This paper is concerned with the determination of reorder points and safety-stock levels for situations where both the demand and lead-time distributions are discrete and independent. Formulas are developed for computing exact probabilities for the lead-time demand distribution on the basis of empirical distributions. Practitioners can use the model to obtain exact probabilities for situations where the computational burden is justified, while academicians can use the model to evaluate heuristic approaches to the reorder-point problem.     

Consignment or wholesale: Retailer and supplier preferences and incentives for compromise

We consider two independently managed parties, a retailer and a supplier, that are considering either a wholesale or a consignment contract to produce and market a single good. Both parties have an interest in reaching an agreement, but their first choice of contract type are generally not the same. We define the strength of retailer and supplier preferences for their respective choices of contract type as the ratio of their expected profits for their first choice of contract type over that for the alternative contract type. We study how uncontrollable factors as well as controllable factors affect the strength of retailer and supplier contract preferences. We develop incentive payments that can potentially be used to increase the likelihood of success in negotiating an agreement.