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Author Letelier, O.R.; Espinoza, D.; Goycoolea, M.; Moreno, E.; Munoz, G. doi  openurl
  Title Production Scheduling for Strategic Open Pit Mine Planning: A Mixed-Integer Programming Approach Type
  Year 2020 Publication Operations Research Abbreviated Journal Oper. Res.  
  Volume 68 Issue 5 Pages 1425-1444  
  Keywords open pit mining; production scheduling; column generation; heuristics; cutting planes; integer programming applications  
  Abstract Given a discretized representation of an ore body known as a block model, the open pit mining production scheduling problem that we consider consists of defining which blocks to extract, when to extract them, and how or whether to process them, in such a way as to comply with operational constraints and maximize net present value. Although it has been established that this problem can be modeled with mixed-integer programming, the number of blocks used to represent real-world mines (millions) has made solving large instances nearly impossible in practice. In this article, we introduce a new methodology for tackling this problem and conduct computational tests using real problem sets ranging in size from 20,000 to 5,000,000 blocks and spanning 20 to 50 time periods. We consider both direct block scheduling and bench-phase scheduling problems, with capacity, blending, and minimum production constraints. Using new preprocessing and cutting planes techniques, we are able to reduce the linear programming relaxation value by up to 33%, depending on the instance. Then, using new heuristics, we are able to compute feasible solutions with an average gap of 1.52% relative to the previously computed bound. Moreover, after four hours of running a customized branch-and-bound algorithm on the problems with larger gaps, we are able to further reduce the average from 1.52% to 0.71%.  
  Address [Rivera Letelier, Orlando] Univ Adolfo Ibanez, Doctoral Program Ind Engn & Operat Res, Santiago 7941169, Chile, Email: orlando.rivera@uai.cl;  
  Corporate Author Thesis  
  Publisher Informs Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0030-364x ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000574409100008 Approved  
  Call Number UAI @ alexi.delcanto @ Serial 1250  
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Author Alvarez-Miranda, E.; Chace, S.; Pereira, J. doi  openurl
  Title Assembly line balancing with parallel workstations Type
  Year 2021 Publication International Journal Of Production Research Abbreviated Journal Int. J. Prod. Res.  
  Volume Early Access Issue Pages 21 pp  
  Keywords Line balancing; parallel stations; dynamic programming; hybrid metaheuristic; matheuristic  
  Abstract The simple assembly line balancing problem (SALBP) considers work division among different workstations of a serially arranged assembly process to maximise its efficiency under workload (cumulative) and technological (precedence) constraints. In this work, we consider a variant of the SALBP which allows parallel workstations. To study the effect of parallel stations, we propose a new problem (the parallel station assembly line balancing problem or PSALBP) in which the objective is to minimise the number of parallel stations required to obtain the maximum theoretical efficiency of the assembly process. We study the complexity of the problem and identify a polynomially solvable case. This result is then used as a building block for the development of a heuristic solution procedure. Finally, we carry out a computational experiment to identify the characteristics of assembly lines that may benefit from station paralleling and to evaluate the performance of the proposed heuristic.  
  Address [alvarez-Miranda, Eduardo] Univ Talca, Fac Engn, Dept Ind Engn, Curico, Chile, Email: jorge.pereira@uai.cl  
  Corporate Author Thesis  
  Publisher Taylor & Francis Ltd Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0020-7543 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000569837900001 Approved  
  Call Number UAI @ alexi.delcanto @ Serial 1243  
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Author Lespay, H.; Suchan, K. doi  openurl
  Title A case study of consistent vehicle routing problem with time windows Type
  Year 2021 Publication International Transactions In Operational Research Abbreviated Journal Int. Trans. Oper. Res.  
  Volume Early Access Issue Pages 29 pp  
  Keywords vehicle routing; multiperiod routing; distribution logistics; service consistency; customer satisfaction; heuristics  
  Abstract We develop a heuristic for the consistent vehicle routing problem with time windows (ConVRPTW), which is motivated by a real-world application at a food company's distribution center. Besides standard VRPTW restrictions, ConVRPTW assigns each customer just one driver to fulfill his or her orders during the whole multiperiod planning horizon. For each driver and period, a route is sought to serve all their customers with positive demand. For each customer, the number of periods between consecutive orders and the ordered quantities is highly irregular. This causes difficulties in the daily routing, negatively impacting the service level of the company. Similar problems have been studied as ConVRP, where the number of drivers is fixeda priori, and only the total travel time is minimized. Moreover, the clients present no time window constraints, but the visits should be scheduled with a small arrival time variation. In our model, the objective is to minimize the number of drivers. We impose hard time windows but do not consider time consistency in more detail. We compare solutions given by the heuristic with solutions of a mixed-integer linear programming model on a set of small artificial instances and solutions used by the food company on real-world instances. The results show the effectiveness of the heuristic. For the company, we obtain significant improvements in the routing plans, with a lower number of vehicles and a higher rate of orders delivered within the prescribed time window.  
  Address [Lespay, Hernan] Univ Adolfo Ibanez, Fac Ingn & Ciencias, Ave Diagonal Torres 2640, Santiago 7941169, Chile, Email: hlespay@alumnos.uai.cl;  
  Corporate Author Thesis  
  Publisher Wiley Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0969-6016 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000579246000001 Approved  
  Call Number UAI @ alexi.delcanto @ Serial 1232  
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Author Ritt, M.; Pereira, J. doi  openurl
  Title Heuristic and exact algorithms for minimum-weight non-spanning arborescences Type
  Year 2020 Publication European Journal Of Operational Research Abbreviated Journal Eur. J. Oper. Res.  
  Volume 287 Issue 1 Pages 61-75  
  Keywords Minimum-weight non-spanning arborescence; Heuristic; Iterated Local Search; Branch-and-cut  
  Abstract We address the problem of finding an arborescence of minimum total edge weight rooted at a given vertex in a directed, edge-weighted graph. If the arborescence must span all vertices the problem is solvable in polynomial time, but the non-spanning version is NP-hard. We propose reduction rules which determine vertices that are required or can be excluded from optimal solutions, a modification of Edmonds algorithm to construct arborescences that span a given set of selected vertices, and embed this procedure into an iterated local search for good vertex selections. Moreover, we propose a cutset-based integer linear programming formulation, provide different linear relaxations to reduce the number of variables in the model and solve the reduced model using a branch-and-cut approach. We give extensive computational results showing that both the heuristic and the exact methods are effective and obtain better solutions on instances from the literature than existing approaches, often in much less time. (C) 2020 Elsevier B.V. All rights reserved.  
  Address [Ritt, Marcus] Univ Fed Rio Grande do Sul, Inst Informat, Av Bento Goncalves 9500, Porto Alegre, RS, Brazil, Email: marcus.ritt@inf.ufrgs.br;  
  Corporate Author Thesis  
  Publisher Elsevier Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0377-2217 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000541072800005 Approved  
  Call Number UAI @ eduardo.moreno @ Serial 1187  
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Author Pereira, J. pdf  doi
openurl 
  Title Modelling and solving a cost-oriented resource-constrained multi-model assembly line balancing problem Type
  Year 2018 Publication International Journal Of Production Research Abbreviated Journal Int. J. Prod. Res.  
  Volume 56 Issue 11 Pages 3994-4016  
  Keywords assembly line balancing; combinatorial optimisation; lower bound; heuristics; estimation of distribution algorithm  
  Abstract A line balancing problem considers the assignment of operations to workstations in an assembly line. While assembly lines are usually associated to mass production of standardised goods, their advantages have led to their widespread use whenever a product-oriented production system is applicable and the benefits of the labour division and specialisation are significant, even when some of its characteristics may deviate from classical assembly lines. In this work, we study a line balancing problem found in the textile industry in which the line must be balanced for multiple types of goods taking into account resource requirements. In order to solve the problem, a hybrid method that combines classical methods for line balancing with an Estimation of Distribution Algorithm is proposed. Computational experiments show that the new procedure improves upon the state of the art when compared using a benchmark set derived from the literature, as well as when compared using data from the manufacturer that originated this research work.  
  Address [Pereira, Jordi] Univ Adolfo Ibanez, Fac Engn & Sci, Vina Del Mar, Chile, Email: jorge.pereira@uai.cl  
  Corporate Author Thesis  
  Publisher Taylor & Francis Ltd Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0020-7543 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000438403800013 Approved  
  Call Number UAI @ eduardo.moreno @ Serial 889  
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Author Moreno, E.; Beghelli, A.; Cugini, F. pdf  doi
openurl 
  Title Traffic engineering in segment routing networks Type
  Year 2017 Publication Computer Networks Abbreviated Journal Comput. Netw.  
  Volume 114 Issue Pages 23-31  
  Keywords Segment routing; Integer Linear Programming; Heuristic  
  Abstract Segment routing (SR) has been recently proposed as an alternative traffic engineering (TE) technology enabling relevant simplifications in control plane operations. In the literature, preliminary investigations on SR have focused on label encoding algorithms and experimental assessments, without carefully addressing some key aspects of SR in terms of the overall network TE performance. In this study, ILP models and heuristics are proposed and successfully utilized to assess the TE performance of SR-based packet networks. Results show that the default SR behavior of exploiting equal cost multiple paths (ECMP) may lead to several drawbacks, including higher network resource utilization with respect to cases where ECMP is avoided. Moreover, results show that, by properly performing segment list computations, it is possible to achieve very effective TE solutions by just using a very limited number of stacked labels, thus successfully exploiting the benefits of the SR technology. (C) 2017 Elsevier B.V. All rights reserved.  
  Address [Moreno, Eduardo] Univ Adolfo Ibanez, Fac Sci & Engn, Santiago, Chile, Email: eduardo.moreno@uai.cl  
  Corporate Author Thesis  
  Publisher Elsevier Science Bv Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1389-1286 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000395214000003 Approved  
  Call Number UAI @ eduardo.moreno @ Serial 708  
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Author Tarifeno-Gajardo, M.; Beghelli, A.; Moreno, E. pdf  doi
openurl 
  Title Availability-Driven Optimal Design of Shared Path Protection in WDM Networks Type
  Year 2016 Publication Networks Abbreviated Journal Networks  
  Volume 68 Issue 3 Pages 224-237  
  Keywords optical networks; shared path protection; prioritized shared protection; availability-guarantees; integer linear programming; heuristic; wavelength division multiplexing networks  
  Abstract Availability, defined as the fraction of time a network service is operative, is a key network service parameter. Dedicated protection increases availability but also the cost. Shared protection instead decreases the cost, but also the availability. In this article, we formulate and solve an integer linear programming (ILP) model for the problem of minimizing the backup resources required by a shared-protected static optical network whilst guaranteeing an availability target per connection. The main research challenge is dealing with the nonlinear expression for the availability constraint. Taking the working/backup routes and the availability requirements as input data, the ILP model identifies the set of connections sharing backup resources in any given network link. We also propose a greedy heuristic to solve large instances in much shorter time than the ILP model with low levels of relative error (2.49% average error in the instances studied) and modify the ILP model to evaluate the impact of wavelength conversion. Results show that considering availability requirements can lead up to 56.4% higher backup resource requirements than not considering them at all, highlighting the importance of availability requirements in budget estimation. (C) 2016 Wiley Periodicals, Inc.  
  Address [Tarifeno-Gajardo, Marco] Univ Tecn Federico Santa Maria, Dept Elect Engn, Valparaiso, Chile, Email: marco.tarifeno@postgrado.usm.cl  
  Corporate Author Thesis  
  Publisher Wiley-Blackwell Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0028-3045 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:000388289300005 Approved  
  Call Number UAI @ eduardo.moreno @ Serial 678  
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