Jorge M. S. Valente

University of Porto, Oporto, Porto, Portugal

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Publications (31)26 Total impact

  • J. Schaller, J. M. S. Valente
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    ABSTRACT: This paper presents several procedures for developing non-delay schedules for a permutation flow shop with family setups when the objective is to minimize total earliness and tardiness. These procedures consist of heuristics that were found to be effective for minimizing total tardiness in flow shops without family setups, modified to consider family setups and the total earliness and tardiness objective. These procedures are tested on several problem sets with varying conditions. The results show that variable greedy algorithms are effective when solving small problems, but using a genetic algorithm that includes a neighbourhood defined by the sequence of batches of jobs belonging to the same set-up family is effective when solving medium- or large-sized problems. The results also show that if setup times can be reduced a significant reduction in total earliness and tardiness could result.
    Journal of the Operational Research Society 06/2013; · 0.99 Impact Factor
  • A. Singh, Jorge M.S. Valente, Maria R.A. Moreira
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    ABSTRACT: In this paper we present three hybrid heuristics for the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. Our heuristic is a combination of a steady-state genetic algorithm and three improvement procedures. The two computationally less expensive of these three improvement procedures are used inside the genetic algorithm to improve the schedule obtained after the application of genetic operators, whereas the more expensive one is used to improve the best solution returned by the genetic algorithm. We have compared our hybrid approaches against existing recovering beam search and genetic algorithms. The computational results show the effectiveness of our hybrid approaches. Indeed, our hybrid approaches outperformed the existing heuristics in terms of solution quality as well as running time.
    International Journal of Machine Learning and Cybernetics. 02/2012; 3(4):327-333.
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    Jeffrey E. Schaller, Jorge M. S. Valente
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    ABSTRACT: This paper considers a problem in which there is a set of jobs to be sequenced on a single machine. Each job has a weight and the objective is to sequence the jobs to minimize total weighted squared tardiness. A branch-and-bound algorithm is developed for optimally solving the problem. Several dominance conditions are presented for possible inclusion in the branch-and-bound algorithm. The dominance conditions are included in the branch-and-bound algorithm, which is tested on randomly generated problems of various numbers of jobs, due date tightness and due date ranges. The results show that the dominance conditions dramatically improve the efficiency of the branch-and-bound algorithm.
    Computers & Operations Research 01/2012; 39:919-928. · 1.91 Impact Factor
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    Jorge M. S. Valente, Jeffrey E. Schaller
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with weighted quadratic tardiness costs. Several efficient dispatching rules are proposed. These include existing heuristics for the linear problem, as well as procedures suitably adapted to the quadratic objective function. Also, both forward and backward scheduling procedures are considered.The computational results show that the heuristics that specifically take into account the quadratic objective significantly outperform their linear counterparts. Also, the backward scheduling approach proves to be superior, and the difference in performance is even more noticeable for the harder instances.The best of the backward scheduling heuristics is both quite efficient and effective. Indeed, this procedure can quickly generate a schedule even for large instances. Also, its relative deviation from the optimum is usually rather low, and it performs adequately even for the more difficult instances.
    Computers & Operations Research 01/2012; 39:2223-2231. · 1.91 Impact Factor
  • Jeffrey Schaller, Jorge M. S. Valente
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    ABSTRACT: This paper considers the problem of scheduling jobs in a permutation flow shop with the objective of minimising total earliness and tardiness. A genetic algorithm is proposed for the problem. This procedure and five other procedures were tested on problem sets that varied in terms of number of jobs, machines and the tightness and range of due dates. It was found that the genetic algorithm procedure was consistently effective in generating good solutions relative to the other procedures.
    International Journal of Production Research 01/2012; · 1.46 Impact Factor
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. We propose a genetic approach based on a random key alphabet, and present several algorithms based on this approach. These versions differ on the generation of both the initial population and the individuals added in the migration step, as well as on the use of local search. The proposed procedures are compared with the best existing heuristics, as well as with optimal solutions for the smaller instance sizes. The computational results show that the proposed algorithms clearly outperform the existing procedures, and are quite close to the optimum. The improvement over the existing heuristics increases with both the difficulty and the size of the instances. The performance of the proposed genetic approach is improved by the initialization of the initial population, the generation of greedy randomized solutions and the addition of the local search procedure. Indeed, the more sophisticated versions can obtain similar or better solutions, and are much faster. The genetic version that incorporates all the considered features is the new heuristic of choice for small and medium size instances.
    International Journal of Advanced Manufacturing Technology 01/2011; 54(1-4):251-265. · 1.78 Impact Factor
  • Jorge M.S. Valente, Jeffrey E. Schaller
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    ABSTRACT: This paper considers the single machine scheduling problem with linear earliness and quadratic tardiness costs. The research on the version with an inserted idle time focused on an exact approach, while several heuristics were already proposed for the version with no idle time. These heuristics were then the basis for the development of new heuristic procedures for the version with idle time. Some improvement procedures were also considered. The new heuristics outperformed the existing procedures. A genetic algorithm provides the best results in terms of solution quality, but is computationally intensive. One of the backward scheduling dispatching rules provides results of similar quality and can quickly solve even large instances. The new heuristics were also applied, with the appropriate modifications, to the version with no idle time. Again, the new procedures provided better results than the existing heuristics. Therefore, the procedures developed in this paper are the new heuristics of choice for both versions of the considered problem. [Received 09 October 2008; Revised 02 February 2009; Accepted 20 February 2009]
    European Journal of Industrial Engineering. 01/2010; 4(1):99-129.
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    Jorge M. S. Valente, Maria R. A. Moreira
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    ABSTRACT: In this paper, we present greedy randomised dispatching heuristics for the single-machine scheduling problem with quadratic earliness and tardiness costs and no machine idle time. The several heuristic versions differ, on the one hand, on the strategies involved in the construction of the greedy randomised schedules. On the other hand, these versions also differ on whether they employ only a final improvement step or perform a local search after each greedy randomised construction. The proposed heuristics were compared with existing procedures as well as with optimum solutions for some instance sizes. The computational results show that the proposed procedures clearly outperform their underlying dispatching heuristic, and the best of these procedures provide results that are quite close to the optimum. The best of the proposed algorithms is the new recommended heuristic for large instances as well as a suitable alternative to the best existing procedure for the larger of the middle-sized instances.
    International Journal of Advanced Manufacturing Technology 10/2009; 44(9):995-1009. · 1.78 Impact Factor
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    JORGE M. S. VALENTE
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with linear earliness and quadratic tardiness costs, and no machine idle time. We present heuristic algorithms based on the beam search technique. These algorithms include classic beam search procedures, as well as the filtered and recovering variants. Several dispatching rules are considered as evaluation functions, to analyze the effect of different rules on the effectiveness of the beam search algorithms.The computational results show that using better rules improves the performance of the beam search heuristics. The detailed, filtered beam search (FBS) and recovering beam search (RBS) procedures outperform the best existing heuristic. The best results are given by the recovering and detailed variants, which provide objective function values that are quite close to the optimum. For small to medium size instances, either of these procedures can be used. For larger instances, the detailed beam search (DBS) algorithm requires excessive computation times, and the RBS procedure then becomes the heuristic of choice.
    Asia Pacific Journal of Operational Research 01/2009; 26(03):319-339. · 0.30 Impact Factor
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    Pedro Abreu, Carlos Soares, Jorge M. S. Valente
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    ABSTRACT: We present a general methodology to model the behavior of heuristics for the Job-Shop Scheduling that address the problem by solv- ing conflicts between dierent operations on the same machine. Our ap- proach is based on the prediction of the gaps in the operation of machines, which are then combined to estimate the performance of the methods. We tested it using two well know heuristics: Shortest Processing Time and Longest Processing Time. Our results show that it is possible to predict the value of the gaps between consecutive operations from same job, on random instances. However, we fail to predict the relative perfor- mance of the two heuristic. We also analyse the impact of features in the linear model of the gaps to understand the importance of each feature.
    Learning and Intelligent Optimization, Third International Conference, LION 3, Trento, Italy, January 14-18, 2009. Selected Papers; 01/2009
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    Jorge M.S. Valente, Rui A.F.S. Alves
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    ABSTRACT: In this paper, we consider the single machine weighted tardiness scheduling problem with sequence-dependent setups. We present heuristic algorithms based on the beam search technique. These algorithms include classic beam search procedures, as well as the filtered and recovering variants. Previous beam search implementations use fixed beam and filter widths. We consider the usual fixed width algorithms, and develop new versions that use variable beam and filter widths.The computational results show that the beam search versions with a variable width are marginally superior to their fixed value counterparts, even when a lower average number of beam and filter nodes is used. The best results are given by the recovering beam search algorithms. For large problems, however, these procedures require excessive computation times. The priority beam search algorithms are much faster, and can therefore be used for the largest instances.Scope and purposeWe consider the single machine weighted tardiness scheduling problem with sequence-dependent setups. In the current competitive environment, it is important that companies meet the shipping dates, as failure to do so can result in a significant loss of goodwill. The weighted tardiness criterion is a standard way of measuring compliance with the due dates. Also, the importance of sequence-dependent setups in practical applications has been established in several studies.In this paper, we present several heuristics based on the beam search technique. In previous beam search implementations, fixed beam and filter widths have been used. We consider the usual fixed width algorithms, and also develop new versions with variable beam and filter widths.The computational tests show that the beam search versions with a variable width are marginally superior to their fixed value counterparts. The recovering beam search procedures are the heuristic of choice for small and medium size instances, but require excessive computation times for large problems. The priority beam search algorithm is the fastest of the beam search heuristics, and can be used for the largest instances.
    Computers & Operations Research 07/2008; 35(7):2388–2405. · 1.91 Impact Factor
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    Jorge M. S. Valente, José Fernando Gonçalves
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with linear earliness and quadratic tardiness costs, and no machine idle time. We propose a genetic approach based on a random key alphabet. Several genetic algorithms based on this approach are presented. These versions differ on the generation of the initial population, as well as on the use of local search. The proposed procedures are compared with the best existing heuristic, as well as with optimal solutions for the smaller instance sizes. The computational results show that the performance of the proposed genetic approach is improved by the addition of a local search procedure, as well as by the insertion of simple heuristic solutions in the initial population. Indeed, the genetic versions that include either or both of these features not only provide significantly better results, but are also much faster. The genetic versions that use local search are clearly superior to the best existing heuristic, and the improvement in performance increases with both the size and difficulty of the instances. These procedures are also quite close to the optimum, and provided an optimal solution for most of the test instances.
    Computers & Operations Research 02/2008; · 1.91 Impact Factor
  • JORGE M. S. VALENTE
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with linear earliness and quadratic tardiness costs, and no machine idle time. We propose a lower bounding procedure based on the relaxation of the jobs' completion times. Optimal branch-and-bound algorithms are then presented. These algorithms incorporate the proposed lower bound, as well as an insertion-based dominance test.The branch-and-bound procedures are tested on a wide set of randomly generated problems. The computational results show that the branch-and-bound algorithms are capable of optimally solving, within reasonable computation times, instances with up to 20 jobs.
    Asia Pacific Journal of Operational Research 02/2008; 25(02):169-186. · 0.30 Impact Factor
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    ABSTRACT: This paper proposes an evolutionary model that captures the main dynamics of a world where heterogeneous firms and workers interact and co-evolve. Within a micro-meso perspective, the model focuses on the influence of firms' "institutional settings" on industry dynamics, formalizing these settings as firms' labor choices. Benefiting from insights offered by mainstream labor economics, we introduce the dynamic processes of job search, bargaining and matching in an evolutionary framework. The results of a computer simulation model show that in a stable environment there is an initial clear improvement in the average fitness of the population of incumbent firms, which then evolves around an evolutionary stationary threshold. The consideration of endogenous matching and bargaining processes in the labor market results in important frictions. Furthermore, the simulation results show an increasing wage inequality between the two types of workers considered in the model. We also consider the effect of both positive and negative demand shocks. The turbulence in the industry increases (decreases) after the negative (positive) demand shock. As expected, the negative demand shock causes a decrease in the number of vacancies and, consequently, the unemployment rates increase considerably. Following the positive demand shock, on the other hand, the firms slightly increase the number of vacancies, so the behavior in terms of unemployment rates is better than in the model without shocks.
    Journal of Economic Interaction and Coordination 05/2007; · 0.57 Impact Factor
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    Jorge M. S. Valente
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. We propose two different lower bounds, as well as a lower bounding procedure that combines these two bounds. Optimal branch-and-bound algorithms are then presented. These algorithms incorporate the proposed lower bound, as well as an insertion-based dominance test. The lower bounding procedure and the branch-and-bound algorithms are tested on a wide set of randomly generated problems. The computational results show that the branch-and-bound algorithms are capable of optimally solving, within reasonable computation times, instances with up to 20 jobs.
    03/2007;
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    Jorge M.S. Valente, Rui A.F.S. Alves
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    ABSTRACT: In this paper we consider the single machine earliness/tardiness scheduling problem with di?erent release dates and no unforced idle time. We analyse the performance of several dispatch rules, a greedy procedure and a decision theory local search heuristic. The dispatch rules use a lookahead parameter whose value must be specified. We perform some experiments to determine an appropriate value for this parameter. The use of dominance rules to improve the solutions obtained by these heuristics is also considered. The computational results show that the use of the dominance rules can indeed improve the solution quality with little additional computational e?ort. To the best of our knowledge, this is the first analysis of heuristic performance for the early/tardy scheduling problem with release dates and no unforced idle time.
    International Journal of Production Economics 02/2007; 106(1):261-274. · 2.08 Impact Factor
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    Jorge M.S. Valente
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    ABSTRACT: The apparent tardiness cost heuristic is one of the best performing dispatch rules for the weighted tardiness scheduling problem. This heuristic uses a lookahead parameter that has previously been set at a fixed value. We propose two different approaches for determining an appropriate value for this parameter. In the first approach, a function is used to map several instance statistics into an adequate value. The second method uses the characteristics of the current workload to determine an appropriate value each time a scheduling decision is to be made.The computational results show that the new procedures outperform the fixed value approach over a wide range of test instances and workload characteristics. The new versions are therefore suited for application in scheduling systems, since they are capable of adjusting themselves to changes in the workload, and provide important savings over the current fixed value implementations.
    International Journal of Production Economics 02/2007; 106(2):563-573. · 2.08 Impact Factor
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    Jorge M.S. Valente
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    ABSTRACT: This paper considers the single machine scheduling problem with linear earliness and quadratic tardiness costs, and no machine idle time. Several dispatching heuristics are proposed, and their performance is analysed on a wide range of instances. The heuristics include simple scheduling rules, as well as a procedure that takes advantage of the strengths of these rules. Linear early/quadratic tardy dispatching rules are also considered, as well as a greedy-type procedure. Extensive experiments are performed to determine appropriate values for the parameters required by some of the heuristics. The computational tests show that the best results are given by the linear early/quadratic tardy dispatching rule. This procedure is also quite efficient, and can quickly solve even very large instances. [Received 15 December 2006; Revised 20 July 2007; Accepted 24 July 2007]
    European Journal of Industrial Engineering. 02/2007; 1(4):431-448.
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    Jorge M. S. Valente, Rui A. F. S. Alves
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    ABSTRACT: In this paper, we consider the single machine scheduling problem with quadratic earliness and tardiness costs, and no machine idle time. We propose several dispatching heuristics, and analyse their performance on a wide range of instances. The heuristics include simple and widely used scheduling rules, as well as adaptations of those rules to a quadratic objective function. We also propose heuristic procedures that specifically address both the earliness and the tardiness penalties, as well as the quadratic cost function. Several improvement procedures were also analysed. These procedures are applied as an improvement step, once the heuristics have generated a schedule. The computational experiments show that the best results are provided by the heuristics that explicitly consider both early and tardy costs, and the quadratic objective function. Therefore, it is indeed important to specifically address the quadratic feature of the cost function, instead of simply using procedures originally developed for a linear objective function. The heuristics are quite fast, and are capable of quickly solving even very large instances. The use of an improvement step is recommended, since it usually improves the solution quality with little additional computational effort.
    Computers & Operations Research 01/2007; · 1.91 Impact Factor
  • Jorge M. S. Valente
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    ABSTRACT: In this paper, we consider the single machine earliness/tardiness scheduling problem with job-independent penalties, and no machine idle time. Several dispatching heuristics are proposed, and their performance is analysed on a wide range of instances. The heuristics include simple scheduling rules, as well as a procedure that takes advantage of the strengths of each of those rules. We also consider early/tardy dispatching procedures, and a heuristic method based on existing adjacent precedence conditions. An improvement procedure that can be used to improve the schedules generated by the heuristics is also proposed.The computational tests show that the best results are given by the early/tardy dispatching rules. These heuristics are also quite fast, and are capable of quickly solving even very large instances. The use of the improvement procedure is recommended, since it improves the solution quality, with little additional computational effort.
    Computers & Industrial Engineering - COMPUT IND ENG. 01/2007; 52(4):434-447.