34 resultados para Problems solving


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Dissertação de mestrado em Direito dos Contratos e da Empresa

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Tese de Doutoramento em Engenharia Industrial e de Sistemas (PDEIS)

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The Closest Vector Problem (CVP) and the Shortest Vector Problem (SVP) are prime problems in lattice-based cryptanalysis, since they underpin the security of many lattice-based cryptosystems. Despite the importance of these problems, there are only a few CVP-solvers publicly available, and their scalability was never studied. This paper presents a scalable implementation of an enumeration-based CVP-solver for multi-cores, which can be easily adapted to solve the SVP. In particular, it achieves super-linear speedups in some instances on up to 8 cores and almost linear speedups on 16 cores when solving the CVP on a 50-dimensional lattice. Our results show that enumeration-based CVP-solvers can be parallelized as effectively as enumeration-based solvers for the SVP, based on a comparison with a state of the art SVP-solver. In addition, we show that we can optimize the SVP variant of our solver in such a way that it becomes 35%-60% faster than the fastest enumeration-based SVP-solver to date.

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In this paper a comparison between using global and local optimization techniques for solving the problem of generating human-like arm and hand movements for an anthropomorphic dual arm robot is made. Although the objective function involved in each optimization problem is convex, there is no evidence that the admissible regions of these problems are convex sets. For the sequence of movements for which the numerical tests were done there were no significant differences between the optimal solutions obtained using the global and the local techniques. This suggests that the optimal solution obtained using the local solver is indeed a global solution.

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Natural selection favors the survival and reproduction of organisms that are best adapted to their environment. Selection mechanism in evolutionary algorithms mimics this process, aiming to create environmental conditions in which artificial organisms could evolve solving the problem at hand. This paper proposes a new selection scheme for evolutionary multiobjective optimization. The similarity measure that defines the concept of the neighborhood is a key feature of the proposed selection. Contrary to commonly used approaches, usually defined on the basis of distances between either individuals or weight vectors, it is suggested to consider the similarity and neighborhood based on the angle between individuals in the objective space. The smaller the angle, the more similar individuals. This notion is exploited during the mating and environmental selections. The convergence is ensured by minimizing distances from individuals to a reference point, whereas the diversity is preserved by maximizing angles between neighboring individuals. Experimental results reveal a highly competitive performance and useful characteristics of the proposed selection. Its strong diversity preserving ability allows to produce a significantly better performance on some problems when compared with stat-of-the-art algorithms.

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Dissertação de mestrado integrado em Engenharia e Gestão Industrial

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Dissertação de mestrado em Engenharia Eletrónica Industrial e Computadores (área de especialização em Robótica)

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Dissertação de mestrado em Engenharia Mecatrónica

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Dissertação de mestrado em Ciências – Formação Contínua de Professores (área de especialização em Biologia e Geologia)

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Dissertação de mestrado em Engenharia Mecânica

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Dissertação de mestrado integrado em Engenharia e Gestão de Sistemas de Informação

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Tese de Doutoramento em Ciências da Educação (área de especilização em Desenvolvimento Curricular).

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Dissertação de mestrado integrado em Engenharia Civil

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Doctoral Thesis in Juridical Sciences (Specialty in Public Legal Sciences)