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Publicações

Publicações por LIAAD

2005

Beam search algorithms for the early/tardy scheduling problem with release dates

Autores
Valente, JMS; Alves, RAFS;

Publicação
JOURNAL OF MANUFACTURING SYSTEMS

Abstract
This paper presents several beam search algorithms for the single-machine earliness/tardiness scheduling problem with release dates and no unforced idle time. These algorithms include classical beam search procedures, with both priority and total cost evaluation functions, as well as the filtered and recovering variants. Both priority evaluation functions and problem-specific properties were considered for the filtering step used in the filtered and recovering procedures. The computational results show that the recovering beam search algorithms outperform their filtered counterparts, while the priority-based filtering procedure proves superior to the rules-based alternative. The beam search procedure with a total cost function provides very good results but is computationally expensive. The recovering algorithm is quite close in solution quality and is significantly faster, so it can be used to solve even large instances.

2005

An exact approach to early/tardy scheduling with release dates

Autores
Valente, JMS; Alves, RAFS;

Publicação
COMPUTERS & OPERATIONS RESEARCH

Abstract
In this paper, we consider the single machine earliness/tardiness scheduling problem with different release dates and no unforced idle time. The problem is decomposed into weighted earliness and weighted tardiness subproblems. Lower bounding procedures are proposed for each of these subproblems, and the lower bound for the original problem is the sum of the lower bounds for the two subproblems. The lower bounds and several version, of a branch-and-bound algorithm are then tested on a set of randomly generated problems, and instances with up to 30 jobs are solved to optimality. To the best of our knowledge, this is the first exact approach for the early/tardy scheduling problem with release dates and no unforced idle time.

2005

Improved heuristics for the early/tardy scheduling problem with no idle time

Autores
Valente, JMS; Alves, RAFS;

Publicação
COMPUTERS & OPERATIONS RESEARCH

Abstract
A dispatch rule and a greedy procedure are presented for the single machine earliness/tardiness scheduling problem with no idle time and compared with the best of the existing dispatch rules. Both dispatch rules use a lookahead parameter that had previously been set at a fixed value. We develop functions that map some instance statistics into appropriate values for that parameter. We also consider the use of dominance rules to improve the solutions obtained by the heuristics. The computational results show that the function-based versions of the heuristics outperform their fixed value counterparts and that the use of the dominance rules can indeed improve solution quality with little additional computational effort.

2005

Filtered and recovering beam search algorithms for the early/tardy scheduling problem with no idle time

Autores
Valente, JMS; Alves, RAFS;

Publicação
COMPUTERS & INDUSTRIAL ENGINEERING

Abstract
In this paper, we present filtered and recovering beam search algorithms for the single machine earliness/tardiness scheduling problem with no idle time, and compare them with existing neighbourhood search and dispatch rule heuristics. Filtering procedures using both priority evaluation functions and problem-specific properties have been considered. The computational results show that the recovering beam search algorithms outperform their filtered counterparts, while the priority-based filtering procedure proves superior to the rules-based alternative. The best solutions are given by the neighbourhood search algorithm, but this procedure is computationally intensive and can only be applied to small or medium size instances. The recovering beam search heuristic provides results that are close in solution quality and is significantly faster, so it can be used to solve even large problems.

2005

Protein sequence classification through relevant sequence mining and Bayes Classifiers

Autores
Ferreira, PG; Azevedo, PJ;

Publicação
PROGRESS IN ARTIFICIAL INTELLIGENCE, PROCEEDINGS

Abstract
We tackle the problem of sequence classification using relevant subsequences found in a dataset of protein labelled sequences. A subsequence is relevant if it is frequent and has a minimal length. For each query sequence a vector of features is obtained. The features consist in the number and average length of the relevant subsequences shared with each of the protein families. Classification is performed by combining these features in a Bayes Classifier. The combination of these characteristics results in a multi-class and multi-domain method that is exempt of data transformation and background knowledge. We illustrate the performance of our method using three collections of protein datasets. The performed tests showed that the method has an equivalent performance to state of the art methods in protein classification.

2005

Protein sequence pattern mining with constraints

Autores
Ferreira, PG; Azevedo, PJ;

Publicação
KNOWLEDGE DISCOVERY IN DATABASES: PKDD 2005

Abstract
Considering the characteristics of biological sequence databases, which typically have a small alphabet, a very long length and a relative small size (several hundreds of sequences), we propose a new sequence mining algorithm (gIL). gIL was developed for linear sequence pattern mining and results from the combination of some of the most efficient techniques used in sequence and itemset mining. The algorithm exhibits a high adaptability, yielding a smooth and direct introduction of various types of features into the mining process, namely the extraction of rigid and arbitrary gap patterns. Both breadth or a depth first traversal are possible. The experimental evaluation, in synthetic and real life protein databases, has shown that our algorithm has superior performance to state-of-the art algorithms. The use of constraints has also proved to be a very useful tool to specify user interesting patterns.

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