Publications
8 results found
Afèche P, Liu Z, Maglaras C, 2023, Ride-Hailing Networks with Strategic Drivers: The Impact of Platform Control Capabilities on Performance, Manufacturing & Service Operations Management, Vol: 25, Pages: 1890-1908, ISSN: 1523-4614
<jats:p> Problem definition: Motivated by ride-hailing platforms such as Uber, Lyft and Didi, we study the problem of matching riders with self-interested drivers over a spatial network. We focus on the performance impact of two operational platform controls—demand-side admission control and supply-side repositioning control—considering the interplay with two practically important challenges: (i) spatial demand imbalances prevail for extended periods of time; and (ii) self-interested drivers strategically decide whether to join the network, and, if so, whether to reposition when not serving riders. Methodology/results: We develop and analyze the steady-state behavior of a novel game-theoretic fluid model of a two-location, four-route loss network. First, we fully characterize and compare the steady-state system equilibria under three control regimes, from minimal control to centralized control. Second, we provide insights on how and why platform control impacts equilibrium performance, notably with new findings on the role of admission control: the platform may find it optimal to strategically reject demand at the low-demand location even if drivers are in excess supply, to induce repositioning to the high-demand location. We provide necessary and sufficient conditions for this policy. Third, we derive upper bounds on the platform’s and drivers’ benefits caused by increased platform control; these are more significant under moderate capacity and significant cross-location demand imbalance. Managerial implications: Our results contribute important guidelines on the optimal operations of ride-hailing networks. Our model can also inform the design of driver compensation structures that support more centralized network control. </jats:p><jats:p> Supplemental Material: The e-companion and Supplemental Material are available at https://doi.org/10.1287/msom.2023.1221 . </jats:p>
Afeche P, Liu Z, Maglaras C, 2023, Ride-hailing networks with strategic drivers: the impact of platform control capabilities on performance, Manufacturing & Service Operations Management, Pages: 1-19, ISSN: 1526-5498
Problem definition: Motivated by ride-hailing platforms such as Uber, Lyft and Didi, we study the problem of matching riders with self-interested drivers over a spatial network. We focus on the performance impact of two operational platform controls—demand-side admission control and supply-side repositioning control—considering the interplay with two practically important challenges: (i) spatial demand imbalances prevail for extended periods of time; and (ii) self-interested drivers strategically decide whether to join the network, and, if so, whether to reposition when not serving riders. Methodology/results: We develop and analyze the steady-state behavior of a novel game-theoretic fluid model of a two-location, four-route loss network. First, we fully characterize and compare the steady-state system equilibria under three control regimes, from minimal control to centralized control. Second, we provide insights on how and why platform control impacts equilibrium performance, notably with new findings on the role of admission control: the platform may find it optimal to strategically reject demand at the low-demand location even if drivers are in excess supply, to induce repositioning to the high-demand location. We provide necessary and sufficient conditions for this policy. Third, we derive upper bounds on the platform’s and drivers’ benefits caused by increased platform control; these are more significant under moderate capacity and significant cross-location demand imbalance. Managerial implications: Our results contribute important guidelines on the optimal operations of ride-hailing networks. Our model can also inform the design of driver compensation structures that support more centralized network control.
Federgruen A, Liu Z, Lu J, 2023, Sourcing in an Increasingly Volatile World: Offshoring, Onshoring or Both?, Publisher: Elsevier BV
Federgruen A, Liu Z, Lu J, 2022, Combined pricing and inventory control with multiple unreliable suppliers, Operations Research Letters, Vol: 51, Pages: 60-66, ISSN: 0167-6377
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 general independent supply mechanisms. Under random capacities—one of the special random supply mechanisms—they also extend to suppliers that are positively dependent on each other.
Federgruen A, Liu Z, Lu L, 2022, Dual sourcing: Creating and utilizing flexible capacities with a second supply source, Production and Operations Management, Vol: 31, Pages: 2789-2805, ISSN: 1059-1478
We study a finite horizon, single product, periodic review inventory system with two supply sources and a salvage option. These supply sources are typically capacitated and capacity levels often need to be reserved or installed in advance of the operational planning horizon. The supply sources may thus be differentiated by their lead times, capacities, and fixed and variable order costs. Salvage options allow for inventory reductions and incur fixed cost and variable revenues. We first analyze the tactical problem of determining an optimal procurement strategy under given capacity profiles at the two suppliers. We then address the strategic model in which optimal capacity profiles, both static and dynamically adjusted, are obtained based on two-part capacity contracts. We characterize the structure of optimal procurement strategies when the lead times of the two suppliers differ by a single period and the lead time for salvage opportunities matches that of one of the suppliers. For general lead time combinations, we show that the optimal procurement strategies satisfy monotonicity and limited sensitivity properties, and construct effective heuristics and upper and lower bounds based on our structural results.
Federgruen A, Liu Z, Lu L, 2020, Synthesis and generalization of structural results in inventory management: a generalized convexity property, Mathematics of Operations Research, Vol: 45, Pages: 547-575, ISSN: 0364-765X
We address a general periodic review inventory control model with the simultaneous presence of the following complications: (a) bilateral inventory adjustment options, via procurement orders and salvage sales or returns to the supplier; (b) fixed costs associated with procurement orders and downward inventory adjustments (via salvage sales or returns); and (c) capacity limits associated with upward or downward inventory adjustments. We characterize the optimal adjustment strategy, both for finite and infinite horizon periodic review models, by showing that in each period the inventory position line is to be partitioned into (maximally) five regions. Our results are obtained by identifying a novel generalized convexity property for the value functions, which we refer to as strong (C1K1, C2K2)-convexity. To our knowledge, we recover most existing structural results for models with exogenous demands as special cases of a unified analysis.
Liu Z, Kee Y, Zhou D, et al., 2017, Preconditioned total field inversion (TFI) method for quantitative susceptibility mapping, MAGNETIC RESONANCE IN MEDICINE, Vol: 78, Pages: 303-315, ISSN: 0740-3194
- Author Web Link
- Cite
- Citations: 79
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.