In this paper, an urban aerial delivery problem (UADP) is investigated, where the parcel transportation service is accomplished by drones in an urban setting. The aim of the problem is to minimize the total service co...
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In this paper, an urban aerial delivery problem (UADP) is investigated, where the parcel transportation service is accomplished by drones in an urban setting. The aim of the problem is to minimize the total service completion time, by taking into account of the flow balance, the energy consumption, and the response time window. To fully explore the structure of the UADP, a mixed integer linear programming (MILP) model is constructed based on an arc-flow scheme. However, directly handling the UADP with commercial solvers is time consuming. In order to enhance the responsiveness of urban courier services and speed up the solving process, a set-covering model (UADP-SC) is proposed with a linear programming based relaxation. Then a branch-and-price algorithm is designed with pricing accelerating strategies based on heuristics. The computational experiments show that the proposed branch-and-price algorithm outperforms the off-the-shelf commercial solvers in terms of computation efficiency. In the mean time, the proposed algorithm can also serve to obtain optimal battery swapping and path planing decisions in face of the large-scale urban aerial delivery problem with energy constraints.
Crew planning, involving how to best schedule crew members during a given period, is a significant problem for urban rail transit companies. This paper proposes a new integer linear programming (ILP) model that can si...
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Crew planning, involving how to best schedule crew members during a given period, is a significant problem for urban rail transit companies. This paper proposes a new integer linear programming (ILP) model that can simultaneously optimize urban rail crew scheduling and rostering problems. The proposed ILP model is a set partitioning-based model with only one type of important duty selection variable that connects the two-level problem and circumvents the drawbacks of conventional approaches that usually formulate the crew scheduling and rostering problems separately and couple these two problems through linking constraints. This study demonstrates that the structure of the underlying network used to model the problem enables the development of an effective, heuristic branch-and-price procedure. The study compares the proposed approach with two other decomposition methods, namely Lagrangian relaxation and alternating direction method of multipliers (ADMM), on problems of different sizes and shows that the method provides lower bounds that are on average 16.4% better than Lagrangian relaxation and 5.03% better than ADMM, respectively. Furthermore, the study shows that, with an average optimality gap of 3.28%, the proposed approach obtains high-quality integer solutions to the integrated problem.
Motivated by express and e-commerce companies' distribution practices, we study a two-echelon electric vehicle routing problem. In this problem, fuel-powered vehicles are used to transport goods from a depot to in...
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Motivated by express and e-commerce companies' distribution practices, we study a two-echelon electric vehicle routing problem. In this problem, fuel-powered vehicles are used to transport goods from a depot to intermediate facilities (satellites) in the first echelon, whereas electric vehicles, which have limited driving ranges and need to be recharged at recharging stations, are used to transfer goods from the satellites to customers in the second echelon. We model the problem as an arc flow model and decompose the model into a master problem and pricing subproblem. We propose a branch-and-price algorithm to solve it. We use column generation to solve the restricted master problem to provide lower bounds. By enumerating all the subsets of the satellites, we generate feasible columns by solving the elementary shortest path problem with resource constraints in the first echelon. Then, we design a bidirectional labeling algorithm to generate feasible routes in the second echelon. Comparing the performance of our proposed algorithm with that of CPLEX in solving a set of small-sized instances, we demonstrate the former's effectiveness. We further assess our algorithm in solving two sets of larger scale instances. We also examine the impacts of some model parameters on the solution.
Industry 4.0 technologies, such as artificial intelligence, the internet of things and 3D printing are aiding the manufacturers by complementing their skilled workforce and transforming the way factories are run. This...
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Industry 4.0 technologies, such as artificial intelligence, the internet of things and 3D printing are aiding the manufacturers by complementing their skilled workforce and transforming the way factories are run. This paper studies an integrated production and transportation scheduling problem in the context of the spare parts supply chain by integrating 3D printing with JIT delivery systems. This work aims to find a synchronised production and distribution schedule that minimises the weighted sum of delivery times and transportation costs. Based on the characteristics of the problem, we propose a new set-covering formulation. An enhanced branch-and-price algorithm is designed to solve the problem instances to optimality. To expedite the column generation process, two acceleration strategies are also used. The computational results are in favour of the proposed algorithm and the acceleration strategies. Further, the results indicate that integrating the production and transportation scheduling decisions leads to an average savings of about 16.27% of the total costs.
This paper presents the problem of batching and scheduling jobs belonging to incompatible job families on unrelated-parallel machines. More specifically, we investigate cost-efficient approaches for solving batching a...
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This paper presents the problem of batching and scheduling jobs belonging to incompatible job families on unrelated-parallel machines. More specifically, we investigate cost-efficient approaches for solving batching and scheduling problems concerning the desired lower bounds on batch sizes (LBb), which indirectly has a considerable impact on the production cost. Batch scheduling is a more realistic extension of the traditional group scheduling approach, in which the jobs belonging to a job family can be processed as multiple batches. The objective is to minimize the total weighted job completion time and tardiness subject to a machine- and sequence-dependent setup time, dynamic machine availability and job release times, customer segments and job priority, and different machine capability and eligibility criteria for processing. Solving this type of batch scheduling problem is a big challenge due to the high computational complexity incurred by both the sequencing assignment and batching composition. A machine learning random forest classification algorithm is used for the LBb determination. Then, an efficient mixed-integer linear programming model (MILP) is developed based on the flow conservation constraints of jobs on machines to reduce the computational complexity. By mapping the MILP model onto a network formulation, an equivalent integer set partitioning type formulation is developed for a branch-and-price optimization algorithm. Computational experiments carried out over different sets of instances, indicate the efficiency and effectiveness of the optimization algorithm, compared to the linear relaxation and relaxed MILP models. Regarding the only available benchmark in the literature, the optimization algorithm yields optimal solutions with affordable computational time.
A proper coloring of a given graph is an assignment of a positive integer number (color) to each vertex such that two adjacent vertices receive different colors. This paper studies the Minimum Sum Coloring Problem (MS...
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A proper coloring of a given graph is an assignment of a positive integer number (color) to each vertex such that two adjacent vertices receive different colors. This paper studies the Minimum Sum Coloring Problem (MSCP), which asks for finding a proper coloring while minimizing the sum of the colors assigned to the vertices. We propose the first branch-and-price algorithm to solve the MSCP to proven optimality. The newly developed exact approach is based on an Integer Programming (IP) formulation with an exponential number of variables which is tackled by column generation. We present extensive computational experiments, on synthetic and benchmark DIMACS graphs from the literature, to compare the performance of our newly developed branch-and-price algorithm against three compact IP formulations. On synthetic graphs, our algorithm outperforms the compact formulations in terms of: (i) number of solved instances, (ii) running times and (iii) exit gaps obtained when optimality is not achieved. For the DIMACS instances, our algorithm is competitive with the best compact formulation and provides very strong dual bounds. (C) 2020 Elsevier B.V. All rights reserved.
We consider the robust single-source capacitated facility location problem with uncertainty in customer demands. A cardinality-constrained uncertainty set is assumed for the robust problem. To solve it efficiently, we...
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We consider the robust single-source capacitated facility location problem with uncertainty in customer demands. A cardinality-constrained uncertainty set is assumed for the robust problem. To solve it efficiently, we propose an allocation-based formulation derived by Dantzig-Wolfe decomposition and a branch-and-price algorithm. The computational experiments show that our branch-and-price algorithm outperforms CPLEX in many cases, which solves the ordinary robust reformulation. We also examine the trade-off relationship between the empirical probability of infeasibility and the additional costs incurred and observe that the robustness of solutions can be improved significantly with small additional costs.
We study an extension of the classical Bin Packing Problem, where each item consumes the bin capacity during a given time window that depends on the item itself. The problem asks for finding the minimum number of bins...
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We study an extension of the classical Bin Packing Problem, where each item consumes the bin capacity during a given time window that depends on the item itself. The problem asks for finding the minimum number of bins to pack all the items while respecting the bin capacity at any time instant. A polynomial-size formulation, an exponential-size formulation, and a number of lower and upper bounds are studied. A branch-and-price algorithm for solving the exponential-size formulation is introduced. An overall algorithm combining the different methods is then proposed and tested through extensive computational experiments. (C) 2019 Elsevier Ltd. All rights reserved.
Freight train formation plan is the basic technical document of railway freight transport organization, it decides the efficiency of railway freight transport. In this paper, we introduce the train formation plan opti...
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ISBN:
(纸本)9781728147628
Freight train formation plan is the basic technical document of railway freight transport organization, it decides the efficiency of railway freight transport. In this paper, we introduce the train formation plan optimization problem in railway network. Then we propose the 0-1 integrated optimization model with the object function to minimize the sum of accumulation time, running time and transit time. According to the characteristics of the model, an improved solution algorithm is designed based on the branch-and-price algorithm. The algorithm is programmed in C# language to solve the model. Finally, the computation results on a case study of simplified China's railway network with 14 large marshalling stations demonstrate the effectiveness and feasibility of the proposed optimization method, which shows the application on the actual railway engineering industry.
This study introduces the multi-trip multi-repairman problem with time windows where an integrated traveling cost involving distance-dependent and time-dependent costs needs to be minimized. The problem is formulated ...
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This study introduces the multi-trip multi-repairman problem with time windows where an integrated traveling cost involving distance-dependent and time-dependent costs needs to be minimized. The problem is formulated as two mixed integer programming models. A branch-and-price algorithm is proposed, in which two route-generating approaches are devised to handle the pricing sub-problem. A large number of instances are randomly generated based on an actual service network of China. The proposed algorithm is validated based on these instances and compared to the direct solving method using Cplex. The comparison to the single-trip mode indicates the advantages of the multi-trip mode.
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