Journal Articles by Burcu Keskin
We present an improved formulation for the maximum coverage patrol routing problem (MCPRP). The m... more We present an improved formulation for the maximum coverage patrol routing problem (MCPRP). The main goal of the patrol routing problem is to maximize the coverage of critical highway stretches while ensuring feasibility of routes and considering the availability of resources. By investigating the structural properties of the optimal solution, we formulate a new, improved mixed integer program that can solve real life instances to optimality within seconds, where methods proposed in prior literature fail to find a provably optimal solution within an hour. The improved formulation provides enhanced highway coverage for both randomly generated and real life instances. We show an average increase in coverage of nearly 20% for the randomly generated instances provided in literature, with a best case increase over 46%. Similarly, for the real life instances, we close the optimality gap within seconds and demonstrate an additional coverage of over 13% in the best case. The improved formulation also allows for testing a number of real life scenarios related to multi-start routes, delayed starts at the beginning of the shifts, and taking a planned break during the shift. Being able to solve these scenarios in short durations help decision and policy makers to better evaluate resource allocation options while serving public.
Papers by Burcu Keskin
Computers & Operations Research, Dec 1, 2010
We examine a generalized vendor selection problem of a multi-store firm where the goal is the sim... more We examine a generalized vendor selection problem of a multi-store firm where the goal is the simultaneous determination of (i) the set of vendors the firm should work with and (ii) how much each store should order from the selected vendors. In addition to the typical costs associated with vendor selection and delivery between the vendors and their assigned stores, we explicitly consider the inventory-related costs and decisions of the stores. We emphasize the relationship between facility location applications and the problem at hand, and we propose an integrated vendor selection and inventory optimization model. Also, arguing that our model creates a venue for precise incorporation of realistic capacity constraints, we model throughput and dispatch capacities, explicitly. The model is a challenging mixed integer nonlinear program for which we propose an efficient solution approach that relies on Generalized Benders Decomposition (GBD).
Computers & Operations Research, Oct 1, 2007
We consider a fixed charge two-stage location problem in which a given number of intermediate tra... more We consider a fixed charge two-stage location problem in which a given number of intermediate transshipment points are to be located between the supply plants and the customer locations. Both plants and transshipment points are capacitated. Scatter search is a population-based heuristic that has been applied to several combinatorial optimization problems. We develop an efficient scatter search-based heuristic approach with hybrid improvements including local search and path-relinking routines. Computational results demonstrate the effectiveness of the heuristic even for realistic problems with larger instances and tighter capacities.
European Journal of Operational Research, Apr 1, 2018
We consider an attractive orienteering problem for planning entertainment events. Specifically, w... more We consider an attractive orienteering problem for planning entertainment events. Specifically, we seek to determine a profit-maximizing tour and event plan among a set of candidate locations over a fixed time horizon. The revenue from a particular event depends on the total attendance. We approximate the total attendance to events using a time-varying attraction measure that accounts for the event location and time as well as events nearby in location and time. The influence of events nearby in location and time is known as the performance shadow. The profit calculation accounts for costs associated with travel to locations and holding events. We formulate a mixed-integer programming model that considers several practical constraints. However, the computational complexity of the problem forces us to develop local search and scatter search based heuristic methods to solve larger instances. We compare the performance of the exact formulation and heuristics using test cases based on regional and national tours within the continental U.S and a real life scenario based on U2's 2017 Joshua Tree tour. A scatter search-based heuristic outperforms all other methods in the experiment. This heuristic is able to find optimal solutions for smaller instances that are solved optimally by a commercial solver. For larger instances, the heuristic outperforms the profit of the best feasible solution returned by the commercial solver by 32.0%. Finally, for the real life comparison, the scatter search based heuristic improves the profit associated with the CPLEX solution and the actual tour by 52.9% and 16.5%, respectively.
The case for women, May 9, 2022
INFORMS Journal on Applied Analytics, 2020
We review 50 years of research published in INFORMS Journal on Applied Analytics (IJAA), formerly... more We review 50 years of research published in INFORMS Journal on Applied Analytics (IJAA), formerly named Interfaces. This historical review considers more than 3,000 publications and details the journal’s coverage evolution over five decades. We identify topics, industries, companies, and organizations that have played a significant role in positioning the journal as INFORMS’ premier outlet regarding the applications of operations research (OR) in practice. Our goal is to use historical observations to discuss the current state of the journal and reflect on the future, especially related to the increasingly popular area of analytics. We provide perspectives regarding how the fields of OR and analytics may continue to evolve as well as how researchers, practitioners, and IJAA can contribute to the continuing evolution of these two fields.
disciplines that comprise transportation through the mechanisms of education, research, and techn... more disciplines that comprise transportation through the mechanisms of education, research, and technology transfer while serving as a university-based center of excellence. ” The UTCA strategic plan contains six goals that support this mission: multiple transportation; Human Resources – increase the number of students, faculty, and staff who are attracted to and substantively of involved in the undergraduate, graduate, and professional programs of UTCA; Education – conduct a multidisciplinary program of coursework and experiential learning that reinforces the theme
of UTCA is “to advance the technology and expertise in the mission disciplines that comprise tran... more of UTCA is “to advance the technology and expertise in the mission disciplines that comprise transportation through the mechanisms of education, research, and technology transfer while serving as a university-based center of excellence. ” The UTCA strategic plan contains six goals that support this mission: multiple transportation; Human Resources – increase the number of students, faculty, and staff who are attracted to and substantively of involved in the undergraduate, graduate, and professional programs of UTCA;
Production and Operations Management, 2020
Computers & Operations Research, 2015
ABSTRACT We present an improved formulation for the maximum coverage patrol routing problem (MCPR... more ABSTRACT We present an improved formulation for the maximum coverage patrol routing problem (MCPRP). The main goal of the patrol routing problem is to maximize the coverage of critical highway stretches while ensuring the feasibility of routes and considering the availability of resources. By investigating the structural properties of the optimal solution, we formulate a new, improved mixed integer program that can solve real life instances to optimality within seconds, where methods proposed in prior literature fail to find a provably optimal solution within an hour. The improved formulation provides enhanced highway coverage for both randomly generated and real life instances. We show an average increase in coverage of nearly 20% for the randomly generated instances provided in the literature, with a best case increase over 46%. Similarly, for the real life instances, we close the optimality gap within seconds and demonstrate an additional coverage of over 13% in the best case. The improved formulation also allows for testing a number of real life scenarios related to multi-start routes, delayed starts at the beginning of the shifts, and taking a planned break during the shift. Being able to solve these scenarios in short durations help decision and policy makers to better evaluate resource allocation options while serving public.
Journal of the Operational Research Society, 2010
Computers & Operations Research, 2007
Computers & Operations Research, 2010
In this research, the integrated sourcing and inventory policy problem in a pharmaceutical distri... more In this research, the integrated sourcing and inventory policy problem in a pharmaceutical distribution company is investigated. In order to select the superior solution, a new tool is introduced. Sourcing is one of the most critical issues in pharmaceutical industry. In addition, drug inventory shortages can cause irreparable humanitarian crises. However, only a limited number of studies has been focused on integrated sourcing and inventory policy of drugs so far. In real-world problems, it is difficult to calculate the exact cost of inventory shortage such as company reputation and humanitarian crises. To overcome this obstacle, in this study, the number of shortage is considered as a separate objective. Likewise, demands of the distributors and breakdowns of suppliers are stochastic, and due to the complicated nature of the problem is difficult to calculate the objective function by using classic methods. So, simulation is used for estimating the objectives of the problem. It's been proved that the problem of this study is NP-Hard. Therefore, a metaheuristic multi-objective particle swarm optimization (MOPSO) method is used to find the optimal solution. To test the reliability of the model and the proposed algorithm, a real drug distributing problem is used and after estimating a Pareto front, the best answer is chosen by The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method.
INFORMS Journal on Applied Analytics
INFORMS Transactions on Education
On Monday morning, Alice Smith, vice president of supply chain (VP-SC) for GreatDeal, sat at her ... more On Monday morning, Alice Smith, vice president of supply chain (VP-SC) for GreatDeal, sat at her desk wondering how she and Rosie Dartmouth, the supply chain executive for NewChicken, are going to navigate the merger between their two companies. The merger was finalized last Friday, and NewChicken is now absorbed into GreatDeal. This week, Alice and Rosie, along with their team of experts, have to start the long and arduous process of reconfiguring their now combined supply chains to ensure the most profitable path for the company. Alice and Rosie are expected to give a presentation to the new chief executive officer, Michelle Shalhoub. The expectations from the merger are high, and there is no room for error. Furthermore, Ms. Shalhoub is known for asking for multiple competitive proposals so that she has the option to choose the best one. Depending on which proposal Ms. Shalhoub accepts, Alice may stay in her position as a VP or she may lose her title and office to Rosie. Hence, th...
INFORMS Transactions on Education
In this case study, we consider the design and redesign of an omni-channel supply chain, followin... more In this case study, we consider the design and redesign of an omni-channel supply chain, following a merger of two existing companies. Prior to the merger, each company has their existing supply chain and operational strengths. Specifically, one company is a more established brick-and-mortar chain and the other is a web-based, e-commerce retailer. Postmerger, they need to evaluate the supply chain structure in terms of sales channels, distribution and fulfillment strategies, and inventory management (especially for three specific groups of products). The case study presents information regarding the market conditions that forced the two companies to merge and offers information to evaluate two competing proposals from senior executives regarding navigating the integration of the online and physical supply chains. The case article discusses the role of this integrated problem within a supply chain management or an inventory management course. In the case article, we present a literat...
Journal of Data, Information and Management
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Journal Articles by Burcu Keskin
Papers by Burcu Keskin