موجودی موفق فروشنده با یک تولید کننده توانا و خرده فروشان چندگانه: رهبری خرده فروش در مقابل رهبری تولید کننده

Considering a supply chain composed of a single capacitated manufacturer and multiple retailers, we model a Stackelberg game vendor managed inventory framework under two scenarios: in the first, we follow the traditional approach wherein the manufacturer is the leader; in the second, we let one of the retailers act as the dominant player of the supply chain. Is retailer dominance a preferred outcome by all retailers? Can the supply chain efficiency be improved by having the dominance gravitated from the manufacturer to one of the retailers? Solving the corresponding MINLP problems, we provide some insights using numerical examples.

Reducing inventory levels of finished products is a major supply chain management challenge. Recent developments in information technology have facilitated the emergence of new cooperative supply chain contracts such as vendor managed inventory (VMI). VMI is an inventory management strategy whereby the upstream vendor manages the downstream retailers’ inventories. It allows the vendor to gain access to inventory and market-related information of the retailers he supplies. This strategy is increasingly being adopted by retailers and their suppliers alike as it benefits both of them: the retailer can improve his fill rates and decrease inventory stockouts, while the supplier, by having access to the downstream market information, enjoys the benefits of better production planning. Additionally, VMI contracts make the downstream retailers sticky, in the sense that they are less likely to switch to a competitive supplier. Examples of successful implementation of VMI strategies are abundant. For instance, Barilla, after adopting a VMI strategy, became the largest pasta manufacturer in the world in 1990. Other examples, include retailers such as Home Depot, Kmart, Dillard Department Stores, and JCPenney, who are often referred to as the early adopters of VMI strategies. While the mainstream supply chain literature, in most instances, considers the upstream member of the supply chain as the leader, reality provides evidence that the retailers may, in fact, play a dominant role in the interaction between them. An example of such a powerful retailer is Wal-Mart, who continually exerts pressure on its suppliers to reduce their wholesale prices and improve delivery times. Messinger and Narasimhan (1995) provide a discussion on how the bargaining power has shifted to the retailers in the grocery channel. Modeling powerful retailers, i.e., the bargaining power shifts downstream, may result in different optimal decisions by the members of the supply chain than when the supply chain is lead by the manufacturer. Ertek and Griffen (2002) investigate the impact of shifting power from the manufacturer to the retailer on price structure and profits in a two stage supply chain. The dominance of powerful retailers raises concerns about the optimality of previously derived results of VMI contracts. Namely, VMI contracts could be set off by retailers such as Wal-Mart and Home Depot, and then the supplying manufacturer could end up offering the same VMI contract to all its downstream retailers. Having the same VMI contract available for all retailers was assumed e.g. by Yang and Zhou (2006), Yuang et al. (2006), and Yu et al. (2009). Moreover, offering the same contract for all retailers is very useful in practice, because it can shield manufacturers from antitrust litigation under Robinson-Patman act ( Iyer, 1998). Iyer (1998) shows that offering similar contracts to all the retailers is sufficient only in markets with substantial locational differentiation. To that end, we formulate the inventory decisions in the supply chain using a Stackelberg framework. We first consider the benchmark setting whereby the manufacturer is the leader and offer the same VMI contract to all retailers. Thereafter, we allow one of the retailers to act as the dominant retailer. This retailer sets forward the initial part of the VMI contract, which stands valid also for the VMI contract the manufacturer later offers to the remaining retailers. The two scenarios are formulated as a two-stage mixed integer nonlinear problems for the leader and the followers, respectively. We transform these problems into a single nonlinear problem by adding the followers’ responses into the leader optimization problem. We solve the general nonlinear problem using an appropriate solver and the results are illustrated through numerical examples. We find that the leader retailer enjoys the benefits of leadership in terms of higher profits and lower fraction of backlogging compared to the manufacturer leadership. Also, retailer leadership decreases the product wholesale price and consequently, the market price of the product, which is a plausible outcome for customers. We compare the supply chain overall efficiency when the manufacturer is the leader versus different settings for retailer leaders and we find that the overall efficiency of the supply chain increases as the leader retailer market scale decreases. The rest of the paper is organized as follows: Section 2 reviews pertinent literature; Section 3 presents the VMI problem formulation; Section 4 studies the benchmark model with the manufacturer being the leader, while Section 5 considers the case of a powerful retailer; finally, Section 6 concludes.

In this paper we formulated a vendor managed inventory, VMI, supply chain that consists of a single capacity-constrained manufacturer and multiple retailers. Using a Stackelberg framework, we raised the question: Are retailers, manufacturers, and entire supply chain better off under manufacturer dominance, or when dominance shifts to one of the retailers? We formulated each player's profit maximization problem as a MINLP. We investigated the retailer leader problem as well as the manufacturer leader problem, and we used the latter as a benchmark for the proposed retailer leader setting. We varied the supply chain parameters to understand the behavior of the system under various settings. Based on the numerical analysis, it appears that retailer dominance, in general, results in higher supply chain efficiency. This study has shown that the highest overall efficiency can be achieved, when a retailer dominates the supply chain, is when the leader has the lowest market scale among the retailers. And the lowest supply chain efficiency occurs when the leader has the highest market scale. While the leader retailer profit increases with respect to the manufacturer leader case, the manufacturer always favor to be the leader in the supply chain because he has higher profits. One obvious finding to emerge from this study is that; the manufacturer's parameters and the market-related parameters of retailers have significant impact on the system optimal results and each member in the supply chain profits. Any change in a retailer's market characteristics affect the retailer itself in addition to the vendor in the supply chain only, but does not much affect other retailers decisions. If a VMI supply chain is dominated by a retailer, the manufacturer benefits much less and the retailers (leader and followers) have increased net profits only if the leader retailer has a small market. Other retailers markets may benefit from this change of strategies in the supply chain depending on their market scale. In future research, this work could be expanded by investigating the leader retailer problem when the leader has a unique contract with the manufacturer instead of our assumption that all retailers have identical contracts. This can be done by offering a menu of prices for retailers based on the quantity they consume. The more they order, the lower is the wholesale price. Considering uncapacitated manufacturer could be an another extension to this work since, as we have shown, the limited capacity of the manufacturer has played a vital role in the model outcomes.