Papers by Sachin Jayaswal
We study a duopoly market in which customers are heterogeneous in their sensitivity to price and ... more We study a duopoly market in which customers are heterogeneous in their sensitivity to price and leadtime, and can be segmented as price sensitive or time sensitive. Each rm tailors (dierentiates) its products/services for the two customer classes solely based on price and the corresponding guaranteed leadtime. Our objective is to understand how competition aects price and leadtime dierentiation of the rms since the extant literature reports very contradicting results. Our results suggest that when rms use dedicated resources to serve the two market segments, pure price competition always tends to decrease individual prices as well as price dierentiation, irrespective of the market behavior. Further, the eect of competition is more pronounced when customers
RePEc: Research Papers in Economics, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
RePEc: Research Papers in Economics, Nov 7, 2013
The advent of Just-in-Time (JIT) and Group Technology philosophies has popularized Ushaped assemb... more The advent of Just-in-Time (JIT) and Group Technology philosophies has popularized Ushaped assembly lines, which help overcome many of the disadvantages, like line inflexibility, job monotony, large inventories, etc., typically associated with straight assembly lines. Although U-shaped layout has demonstrated it supremacy over the traditional straight layout, the problem of U-shaped assembly line balancing (ULB) is much more complex. The extant literature on ULB assumes that each assembly task requires a fixed (or no) equipment and a fixed number of workers. However, it is often desirable to reduce certain task times by assigning more workers or alternative equipments at a given workstation. The problem in such cases is to assign not only the task but also resource alternatives (number of workers and equipment type) to workstations. Research on such resource dependent U-shaped assembly line balancing (RDULB) is scarce. We address the problem of RDULB and propose a Simulated Annealing (SA) based metaheuristic, which gives optimal solution for most of the small-to-medium problem instances. For very large problems, while SA generates a good feasible solution within half an hour to 1.5 hours, Cplex is unable to find a single feasible solution even after 10 times the CPU time required by SA.
We study a duopoly market in which customers are heterogeneous in their sensitivity to price and ... more We study a duopoly market in which customers are heterogeneous in their sensitivity to price and leadtime, and can be segmented as price sensitive or time sensitive. Each rm tailors (dierentiates) its products/services for the two customer classes solely based on price and the corresponding guaranteed leadtime. Our objective is to understand how competition aects price and leadtime dierentiation of the rms since the extant literature reports very contradicting results. Our results suggest that when rms use dedicated resources to serve the two market segments, pure price competition always tends to decrease individual prices as well as price dierentiation, irrespective of the market behavior. Further, the eect of competition is more pronounced when customers
Journal of Manufacturing Systems, Oct 1, 2014
The advent of Just-in-Time (JIT) and Group Technology philosophies has popularized Ushaped assemb... more The advent of Just-in-Time (JIT) and Group Technology philosophies has popularized Ushaped assembly lines, which help overcome many of the disadvantages, like line inflexibility, job monotony, large inventories, etc., typically associated with straight assembly lines. Although U-shaped layout has demonstrated it supremacy over the traditional straight layout, the problem of U-shaped assembly line balancing (ULB) is much more complex. The extant literature on ULB assumes that each assembly task requires a fixed (or no) equipment and a fixed number of workers. However, it is often desirable to reduce certain task times by assigning more workers or alternative equipments at a given workstation. The problem in such cases is to assign not only the task but also resource alternatives (number of workers and equipment type) to workstations. Research on such resource dependent U-shaped assembly line balancing (RDULB) is scarce. We address the problem of RDULB and propose a Simulated Annealing (SA) based metaheuristic, which gives optimal solution for most of the small-to-medium problem instances. For very large problems, while SA generates a good feasible solution within half an hour to 1.5 hours, Cplex is unable to find a single feasible solution even after 10 times the CPU time required by SA.
European Journal of Operational Research, Sep 1, 2023
European Journal of Operational Research, Apr 1, 2021
The main objective of the Working Paper series of IIMA is to help faculty members, research staff... more The main objective of the Working Paper series of IIMA is to help faculty members, research staff, and doctoral students to speedily share their research findings with professional colleagues and to test out their research findings at the pre-publication stage.
European Journal of Operational Research, Oct 1, 2018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights • This paper studies a bilevel Hub Interdiction and trilevel Hub Protection Problem. • We study efficient methods to reduce the bilevel problem to single level. • We present different closest assignment constraints to enable this reduction. • We propose a Benders Decomposition method that solves large interdiction problems.
European Journal of Operational Research, May 1, 2011
We study a firm selling two products/services, which are differentiated solely in their prices an... more We study a firm selling two products/services, which are differentiated solely in their prices and delivery times, to two different customer segments in a capacitated environment. From demand perspective, when both products are available to all customers, they act as substitutes, affecting each other's demand. Customized products for each segment, on the other hand, result in independent demand for each product. On the supply side, the firm may either share the same capacity to serve the two market segments, or may dedicate capacity for each segment. Our objective is to understand the interaction between product substitution and the firm's operations strategy (dedicated versus shared capacity), and how it shapes the optimal product differentiation strategy. We show that in a highly capacitated system, if the firm decides to move from a dedicated to a shared capacity setting it will need to offer more differentiated products, whether the products are substitutable or not. In contrast, when independent products become substitutable, a more homogeneous pricing scheme results. However, whether the delivery times are more differentiated or more similar depends on the firm's capacity strategy and cost, as well as market characteristics. Moreover, the optimal response to an increase in capacity cost also depends on the firm's operations strategy. In a dedicated capacity scenario, the optimal response is always to offer more homogeneous prices and delivery times. In a shared capacity setting, it is always optimal to quote more homogeneous delivery times, but increase or decrease the price differentiation depending on whether the status-quo capacity cost is high or low, respectively. We demonstrate that the above results are corroborated by real-life practices, and provide a number of managerial implications in terms of dealing with issues like volatile fuel prices.
arXiv (Cornell University), Jul 25, 2023
In this paper, we propose an exact general algorithm for solving non-convex optimization problems... more In this paper, we propose an exact general algorithm for solving non-convex optimization problems, where the non-convexity arises due to the presence of an inverse S-shaped function. The proposed method involves iteratively approximating the inverse S-shaped function through piece-wise linear inner and outer approximations. In particular, the concave part of the inverse S-shaped function is inner-approximated through an auxiliary linear program, resulting in a bilevel program, which is reduced to a single level using KKT conditions before solving it using the cutting plane technique. To test the computational efficiency of the algorithm, we solve a facility location problem involving economies and dis-economies of scale for each of the facilities. The computational experiments indicate that our proposed algorithm significantly outperforms the previously reported methods. We solve non-convex facility location problems with sizes up to 30 potential facilities and 150 customers. The computational experiments indicate that our proposed algorithm converges to the global optimum within a maximum computational time of 3 hours for 95% of the datasets. For almost 60 percent of the test cases, the proposed algorithm outperforms the benchmark methods by an order of magnitude. The paper ends with managerial insights on facility network design involving economies and dis-economies of scale. One of the important insights points out that it may be optimal to increase the number of production facilities operating under dis-economies of scale with an overall decrease in transportation costs.
arXiv (Cornell University), Jul 20, 2021
We study a general class of quadratic capacitated p-location problems facility location problems ... more We study a general class of quadratic capacitated p-location problems facility location problems with single assignment where a non-separable, non-convex, quadratic term is introduced in the objective function to account for the interaction cost between facilities and customer assignments. This problem has many applications in the field of transportation and logistics where its most well-known special case is the single-allocation hub location problem and its many variants. The non-convex, binary quadratic program is linearized by applying a reformulation-linearization technique and the resulting continuous auxiliary variables are projected out using Benders decomposition. The obtained Benders reformulation is then solved using an exact branch-and-cut algorithm that exploits the underlying network flow structure of the decomposed separation subproblems to efficiently generate strong Pareto-optimal Benders cuts. Additional enhancements such as a matheuristic, a partial enumeration procedure, and variable elimination tests are also embedded in the proposed algorithmic framework. Extensive computational experiments on benchmark instances (with up to 500 nodes) and on a new set of instances (with up to 1,000 nodes) of four variants of single-allocation hub location problems confirm the algorithm's ability to scale to large-scale instances.
RePEc: Research Papers in Economics, 2019
RePEc: Research Papers in Economics, 2018
In this paper, we study the single allocation hub location problem with capacity selection in the... more In this paper, we study the single allocation hub location problem with capacity selection in the presence of congestion at hubs. Accounting for congestion at hubs leads to a non-linear mixed integer program, for which we propose 18 alternate mixed integer second order conic program (MISOCP) reformulations. Based on our computational studies, we identify the best MISOCP-based reformulation, which turns out to be 20−60 times faster than the state-of-the-art. Using the best MISOCP-based reformulation, we are able to exactly solve instances up to 50 nodes in less than half-an-hour. We also theoretically examine the dimensionality of the second order cones associated with different formulations, based on which their computational performances can be predicted. Our computational results corroborate our theoretical findings. Such insights can be helpful in the generation of efficient MISOCPs for similar classes of problems.
RePEc: Research Papers in Economics, 2018
Optimization of charging infrastructure for electric buses is critical for the transition from co... more Optimization of charging infrastructure for electric buses is critical for the transition from conventional buses to electric buses since chargers, especially for chargers since they constitute almost two-thirds of the total charging infrastructure costs. Different modeling frameworks to optimize the charging capacity are developed separately for the depot charging and opportunity charging and tested for the transit network of Navi Mumbai Municipal Transport (India). The models determine the optimal number and capacity of chargers such that the existing bus operational schedules are maintained – a prime requirement of bus operators. Since the route coverage per bus per day would require en-route charging, the opportunity charging model determines the optimal locations for installing these chargers. A sensitivity analysis is also conducted to analyze the effects of the specific energy consumption of the buses and their rated battery capacity on charger selection. These models are first of their kind to be used for electric bus adoption in India. Keywords: Electric bus, charging infrastructure, charging schedule, cost optimization modeling, public transit networks
RePEc: Research Papers in Economics, Mar 7, 2016
We study a nonlinear 0-1 knapsack problem with capacity selection decision, as it arises as a par... more We study a nonlinear 0-1 knapsack problem with capacity selection decision, as it arises as a part of facility location/service system design problems with congestion. The capacity selection decision gives rise to a non-convex objective function. We present two cutting plane based solution approaches: one based on Generalized Benders decomposition based, and the other based on a reformulation of the problem using additional auxiliary variables, followed by outer linearization of a resulting simple concave func- tion in the constraint.
RePEc: Research Papers in Economics, Oct 25, 2016
In this paper, we present computationally efficient formulations for the hub interdiction and hub... more In this paper, we present computationally efficient formulations for the hub interdiction and hub protection problems, which are bi-level and tri-level mixed integer linear programs, respectively. In the hub interdiction problem, the aim is to identify a set of r critical hubs from an existing set of p hubs that when interdicted results in the greatest disruption cost to the hub-andspoke network. Reduction of the bi-level interdiction model to single level is straightforward using Karush-Kuhn-Tucker (KKT) conditions corresponding to the lower level problem; however, this turns out to be computationally inefficient in this context. Therefore, we exploit the structure of the problem using various closest assignment constraints to reduce the hub interdiction problem to single level. The modifications lead to computational savings of almost an order of magnitude when compared against the only model existing in the literature. Further, our proposed modifications offer structural advantages for Benders decomposition, which lead to substantial savings, particularly for large problems. Finally, we study and solve the hub protection problem exactly by utilizing the ideas developed for the hub interdiction problem. The tri-level protection problem is otherwise intractable, and to our best knowledge, has not been solved in the literature.
Elizabeth Jewkes, for her continuous moral, intellectual and financial support during my Ph.D. st... more Elizabeth Jewkes, for her continuous moral, intellectual and financial support during my Ph.D. study at the Department of Management Sciences, University of Waterloo. She has always been available for any help I needed. I would like to express my special thanks to my co-advisor, Dr. Saibal Ray, without whose guidance this thesis would not have been possible. I am very grateful to have had the chance to work with my advisors, who have encouraged me at every step of my Ph.D. study with great patience. My gratitude also goes to the faculty of the Department of Management Sciences for providing me with the foundations for my Ph.D. research. I would like to thank Dr. James H. Bookbinder, Dr. Samir Elhedhli and Dr. Steve Drekic for their time and effort in serving on my Ph.D. committee. My special thanks to Dr. Miguel Anjos and Dr. Benny Martin who have always been available for their friendly advice. I would like to thank all my friends in Waterloo-Kitchener who made my stay in Canada so memorable, especially my great house mates Sarvagya, Akhilesh, Aashish and Guru Prakash, who besides sharing the chores of my kitchen have also shared all my sorrows and happiness in last 4 years. I would also like to thank Emre Celebi, my first friend in the department, Meyappan, Edward, Joe, Bissan and Eman whose company I always enjoyed. My special thanks to my office mate, Navneet Vidyarthi, and his wife, Geetali Vidyarthi, for their love and affection. Finally, I am forever indebted to my parents for their unconditional love and support, and for the sacrifices they have always made to see me realize my dreams in life. I am also indebted to my brother, Suman Jayaswal, my sisters, Sushma Jayaswal and Seema Jayaswal, for sharing my responsibilities towards my parents while I was away from home to pursue my studies. I am specially thankful to my sister, Seema Jayaswal, who trusts me more than I do myself, and has always reminded me of my responsibilities in life. My very special thanks goes to my vi fiancee, Ritika, who has been solidly behind me during the good and bad phases of my life. vii Dedication To my parents for the sacrifices they have always made to see me realize my dreams in life viii Contents List of Tables xiv List of Figures xvi List of Figures 2.1 Schematic representation of a monopolistic model. .. .. .. .. .
We study a firm selling two products/services, which are differentiated solely in their prices an... more We study a firm selling two products/services, which are differentiated solely in their prices and delivery times, to two different customer segments in a capacitated environment. From a demand perspective, when both products are available to all customers, they act as substitutes, affecting each other's demand. Customized products for each segment, on the other hand, result in independent demand for each product. From a supply perspective, the firm may either share the same capacity or may dedicate a different capacity for each segment. Our objective is to understand the interaction between product substitution and the firm's operations strategy (dedicated versus shared capacity), and how this interaction shapes the optimal product differentiation strategy. We show that in a highly capacitated system, if the firm decides to move from a dedicated to a shared capacity setting, it will need to offer more differentiated products, whether the products are substitutable or not. In contrast, when independent products become substitutable, it results in a more homogeneous pricing scheme. Moreover, the optimal response to an increase in capacity cost also depends on the firm's operations strategy. In a dedicated capacity scenario, the optimal response is always to offer more homogeneous prices and delivery times. In a shared capacity setting, it is always optimal to quote more homogeneous delivery times, but to increase or decrease the price differentiation depending on whether the status-quo capacity cost is high or low, respectively.
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Papers by Sachin Jayaswal