Working papers

Abstract: A key feature of many real-world matching markets is congestion, i.e., market participants struggle to find match partners. We characterize congestion in a model of random matching markets where an agent pair must perform an inspection to verify compatibility prior to matching with each other. Motivated by the notion of regret-free stability, we assume agents are only willing to inspect their current favorite agent and will do so only if, upon a successful inspection, that match is guaranteed. We ask when, in large random two-sided markets, will information deadlocks arise in which many agents delay inspections indefinitely awaiting a match guarantee. The market consists of N women and αN men. We obtain a sharp characterization of the existence and size of information deadlock as a function of the men-to-women ratio α, women’s average size K of the consideration set, and an inspection’s success probability p, as N grows. Our analysis is inspired by the machinery of message passing and density evolution from statistical physics. We find a phase transition from a deadlock-free regime (where a vanishingly small fraction of agents are stuck waiting) to the information deadlock regime as we increase K, decrease α or decrease p. A number of market design insights emerge from our characterization, for example, the market connectivity K which maximizes the number of matches formed is that which causes the market to be at the phase boundary between the deadlock-free regime and the deadlock regime. Vertical differentiation between agents reduces deadlock, as does a willingness by agents to perform parallel inspections.

2. Sourcing in an Increasingly Volatile World: Offshoring, Onshoring or Both?, with Awi Federgruen and Zhe Liu, under review at Operations Research

Abstract: We study a dual sourcing problem in an increasingly volatile world. We consider two types of volatilities. The first type models fluctuating economic conditions via an underlying Markovmodulated state-of-the-world which affects the two suppliers’ cost structures, capacity limits, and demands. The other type of volatility affects the actual outputs resulting from random supply processes. We develop two approaches to show how the optimal combined ordering strategy from the two suppliers, along with a salvaging policy, can be efficiently computed, and characterize the relatively simple structure of the optimal policies. We also present various comparison results of the expected total costs under different environments. We find that the firm can, by exploiting the dual sourcing options, benefit from environmental volatilities that affect the suppliers’ cost structures or capacity limits; indeed, benefits increase as volatilities increase in specific ways. Numerical studies illustrate these results and reject other reasonable conjectures.

3. Sourcing with Demand Updates, with Awi Federgruen and Zhe Liu, revise and resubmit at Management Science

Abstract: We address a two-stage Newsvendor model in which the mean demand -- but not the actual demand -- at first random itself, gets revealed in midstream, in time to place a second order, albeit that the unit cost price of this second order is higher than that of the original one. The two-stage process is most relevant to many retail organizations, where the retailer has access to two supply options: one with a relatively long lead time where orders need to be placed with much uncertainty about even the mean demand for the season, and a second more expensive option with a much smaller lead time that can be exercised after a signal is revealed, which provides the decision maker with an update of the mean demand. We show that the optimal first-round order can be found by solving a simple ordinary differential equation, while the second-round order is analytically available. We characterize the asymptotic behavior of the initial order, derive analytical upper and lower bounds for this initial procurement, and extend our results to the case where procurement capacities prevail. A numerical study shows the benefits of postponed procurements. We also show necessary and sufficient conditions under which a simple heuristic, suggested by the asymptotic analysis, outperforms the optimal single-stage Newsvendor solution.

4. Allocating Emission Permits Efficiently via Uniform Linear Mechanisms, with Xingyu Lin, submitted (extended abstract appeared in WINE 2023)

Abstract: We study the problem of allocating emission permits in an emissions trading system and provide efficiency guarantee of simple uniform linear allocation mechanisms in the broad class of component-wise concave mechanisms. It was well accepted in the literature that the equilibrium consumer surplus and social welfare are not affected by the initial allocation of emission permits in a deterministic system without trading fractions. However, the initial allocations previously considered were largely restricted to constant ones that do not depend on the firms’ current production decisions. We show that, by allowing more general mechanisms that are component-wise concave in the firm’s production decision, which capture many realistic allocation rules including lump-sum allocations (such as grandfathering), output-based allocations (either top-down or bottom-up), etc., consumer surplus will no longer be independent of the initial allocations. In particular, for N firms operating under Cournot competition that differs in their abatement abilities, uniform linear permit allocation mechanisms are the most efficient, i.e., achieve the maximum equilibrium aggregate production output given the same level of equilibrium emission, hence the maximum consumer surplus. By defining a monopoly’s problem that is equivalent to the original N-firm system, the regulator can thus reduce the search space of N-dimensional allocation mechanisms to a single coefficient. Numerical experiments show that the benefit of uniform linear mechanisms compared to constant ones can be large.

5. Managing Newsvendors via Demand Nudging, with Yilun Chen, submitted

Abstract: The increasingly prevalent "fulfillment by platform" practice in the digital economy presents platforms with the unique challenge of managing their third-party sellers' autonomous inventory decision-making. In this work, we explore a novel idea to mitigate this challenge through nudging demand among sellers, which reshapes their perceived demand and incentivizes them to make platform-favorable inventory decisions. To this end, we study a stylized Stackelberg game between a platform and a continuum of third-party sellers selling substitutable products on the platform. The platform aims to design a demand nudging policy to maximize her profit, while the sellers, in response, determine their inventory according to the post-nudge demand in a newsvendor manner. We establish in closed form the platform's optimal policy. It employs a simple cut-off structure called defluctuating and resembles risk pooling in the centralization setting where the platform can make joint demand-substitution and inventory decisions. Despite the power of this control on the off-equilibrium path, we show that it is Pareto-improving for both the platform and the sellers under a mild condition. Furthermore, when the products are substitutable enough, the platform can achieve the centralization benchmark. On the contrary, if the products are not substitutable enough, the platform's service level to the customers may, in certain primitive regimes, decrease.

Publications

1. Managing Customer Churn via Service Model Control, with Yash Kanoria and Ilan Lobel, Mathematics of Operations Research (2023)

Abstract: We introduce a novel stochastic control model for the problem of a service firm interacting over time with one of its customers. The firm has two service modes available, which differ in their expected reward rates as well as their volatilities (risk). The firm’s objective is to maximize the rewards generated over the customer’s lifetime. Meanwhile, the customer is unsophisticated and might, probabilistically, abandon the system if unsatisfied with recent rewards. We show that the firm’s optimal policy is either myopic or a sandwich policy. A sandwich policy is one where the firm utilizes the myopically optimal service mode when the customer is either very happy or very unhappy but that utilizes the service mode with inferior reward rate when the customer happiness is in a specific interval near the satisfaction threshold. Specifically, the firm should be risk averse when the customer is marginally satisfied and risk seeking when the customer is marginally unsatisfied. We find numerically that the customer lifetime value under the optimal policy is large relative to that under the myopic policy. We also show that our results are robust to a variety of alternative model specifications.

2. Combined Pricing and Inventory Control with Multiple Unreliable Suppliers, with Awi Federgruen and Zhe Liu, Operations Research Letters, Vol: 51 (2023), Pages: 60-66, ISSN: 0167-6377

Abstract: We study a general finite horizon, periodic review combined inventory and pricing model with N suppliers and T periods, where both the demands and the supply mechanisms are random. The random supply mechanisms are of a general type that includes most structures encountered in practice. Demands are price-dependent according to general, stochastic demand functions. We characterize the optimal combined pricing and ordering policies to all N suppliers. The general results pertain to independent supply mechanisms but under random capacities — one of the special random supply mechanisms — they also extend to suppliers that are positively dependent on each other.