H. Edwin Romeijn
Georgia Institute of Technology
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Featured researches published by H. Edwin Romeijn.
European Journal of Operational Research | 2015
Mehmet Önal; H. Edwin Romeijn; Amar Sapra; Wilco van den Heuvel
We consider the economic lot-sizing problem with perishable items (ELS-PI), where each item has a deterministic expiration date. Although all items in stock are equivalent regardless of procurement or expiration date, we allow for an allocation mechanism that defines an order in which the items are allocated to the consumers. In particular, we consider the following allocation mechanisms: First Expiration, First Out (FEFO), Last Expiration, First Out (LEFO), First In, First Out (FIFO) and Last In, First Out (LIFO). We show that the ELS-PI can be solved in polynomial time under all four allocation mechanisms in case of no procurement capacities. This result still holds in case of time-invariant procurement capacities under the FIFO and LEFO allocation mechanisms, but the problem becomes NP-hard under the FEFO and LIFO allocation mechanisms.
European Journal of Operational Research | 2016
Joseph Geunes; H. Edwin Romeijn; Wilco van den Heuvel
In a decentralized two-stage supply chain where a supplier serves a retailer who, in turn, serves end customers, operations decisions based on local incentives often lead to suboptimal system performance. Operating decisions based on local incentives may in such cases lead to a lack of system coordination, wherein one party’s decisions put the other party and/or the system at a disadvantage. While models and mechanisms for such problem classes have been considered in the literature, little work to date has considered such problems under nonstationary demands and fixed replenishment order costs. This paper models such two-stage problems as a class of Stackelberg games where the supplier announces a set of time-phased ordering costs to the retailer over a discrete time horizon of finite length, and the retailer then creates an order plan, which then serves as the supplier’s demand. We provide metrics for characterizing the degree of efficiency (and coordination) associated with a solution, and provide a set of easily understood and implemented mechanisms that can increase this efficiency and reduce the negative impacts of uncoordinated decisions.
Operations Research | 2017
Ilbin Lee; Marina A. Epelman; H. Edwin Romeijn; Robert L. Smith
We consider discounted Markov decision processes (MDPs) with countably-infinite state spaces, finite action spaces, and unbounded rewards. Typical examples of such MDPs are inventory management and queueing control problems in which there is no specific limit on the size of inventory or queue. Existing solution methods obtain a sequence of policies that converges to optimality in value but may not improve monotonically, ie., a policy in the sequence may be worse than preceding policies. Our proposed approach considers countably-infinite linear programming (CILP) formulations of the MDPs (a CILP is defined as a linear program (LP) with countably-infinite numbers of variables and constraints). Under standard assumptions for analyzing MDPs with countably-infinite state spaces and unbounded rewards, we extend the major theoretical extreme point and duality results to the resulting CILPs. Under additional mild assumptions, which are satisfied by several applications of interest, we present a simplex-type algor...
Operations Research | 2018
Zohar M.A. Strinka; H. Edwin Romeijn
We study a class of problems with both binary selection decisions and associated continuous choices that result in stochastic rewards and costs. The rewards are received based on the decision maker’s selection, and the costs depend both on the decisions and realizations of the stochastic variables. We consider a family of risk-based objective functions that contains the traditional risk-neutral expected-value objective as a special case. A combination of rounding and sample average approximation is used to produce solutions that are guaranteed to be close to the optimal solution with high probability. We also provide an empirical comparison of the performance of the algorithms on a set of randomly generated instances of a supply chain example problem. The computational results illustrate the theoretical claims in the paper that, for this problem, high-quality solutions can be found with small computational effort.
Archive | 2005
Joseph Geunes; Yasemin Merzifonluoglu; H. Edwin Romeijn; Kevin Taaffe
Physics in Medicine and Biology | 2016
V Wu; Marina A. Epelman; Hesheng Wang; H. Edwin Romeijn; Mary Feng; Yue Cao; Randall K. Ten Haken; M.M. Matuszak
Naval Research Logistics | 2016
Majid Mohammed Al-Gwaiz; Xiuli Chao; H. Edwin Romeijn
IVHS Technical Report | 1992
H. Edwin Romeijn; Robert Little Smith
IVHS TECHNICAL REPORT ; | 1991
H. Edwin Romeijn; Robert L. Smith
Archive | 2001
Yu-Li Chou; Stephen M. Pollock; H. Edwin Romeijn; Robert L. Smith