14 resultados para Linear and multilinear programming

em Instituto Politécnico do Porto, Portugal


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The ecotoxicological response of the living organisms in an aquatic system depends on the physical, chemical and bacteriological variables, as well as the interactions between them. An important challenge to scientists is to understand the interaction and behaviour of factors involved in a multidimensional process such as the ecotoxicological response.With this aim, multiple linear regression (MLR) and principal component regression were applied to the ecotoxicity bioassay response of Chlorella vulgaris and Vibrio fischeri in water collected at seven sites of Leça river during five monitoring campaigns (February, May, June, August and September of 2006). The river water characterization included the analysis of 22 physicochemical and 3 microbiological parameters. The model that best fitted the data was MLR, which shows: (i) a negative correlation with dissolved organic carbon, zinc and manganese, and a positive one with turbidity and arsenic, regarding C. vulgaris toxic response; (ii) a negative correlation with conductivity and turbidity and a positive one with phosphorus, hardness, iron, mercury, arsenic and faecal coliforms, concerning V. fischeri toxic response. This integrated assessment may allow the evaluation of the effect of future pollution abatement measures over the water quality of Leça River.

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The e-Framework is arguably the most prominent e-learning framework currently in use. For this reason it was selected as basis for modelling a programming exercises evaluation service. The purpose of this type of evaluator is to mark and grade exercises in computer programming courses and in programming contests. By exposing its functions as services a programming exercise evaluator is able to participate in business processes integrating different system types, such as Programming Contest Management Systems, Learning Management Systems, Integrated Development Environments and Learning Object Repositories. This paper formalizes the approaches to be used in the implementation of a programming exercise evaluator as a service on the e-Framework.

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This paper presents a tool called Petcha that acts as an automated Teaching Assistant in computer programming courses. The ultimate objective of Petcha is to increase the number of programming exercises effectively solved by students. Petcha meets this objective by helping both teachers to author programming exercises and students to solve them. It also coordinates a network of heterogeneous systems, integrating automatic program evaluators, learning management systems, learning object repositories and integrated programming environments. This paper presents the concept and the design of Petcha and sets this tool in a service oriented architecture for managing learning processes based on the automatic evaluation of programming exercises. The paper presents also a case study that validates the use of Petcha and of the proposed architecture.

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Recently, operational matrices were adapted for solving several kinds of fractional differential equations (FDEs). The use of numerical techniques in conjunction with operational matrices of some orthogonal polynomials, for the solution of FDEs on finite and infinite intervals, produced highly accurate solutions for such equations. This article discusses spectral techniques based on operational matrices of fractional derivatives and integrals for solving several kinds of linear and nonlinear FDEs. More precisely, we present the operational matrices of fractional derivatives and integrals, for several polynomials on bounded domains, such as the Legendre, Chebyshev, Jacobi and Bernstein polynomials, and we use them with different spectral techniques for solving the aforementioned equations on bounded domains. The operational matrices of fractional derivatives and integrals are also presented for orthogonal Laguerre and modified generalized Laguerre polynomials, and their use with numerical techniques for solving FDEs on a semi-infinite interval is discussed. Several examples are presented to illustrate the numerical and theoretical properties of various spectral techniques for solving FDEs on finite and semi-infinite intervals.

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The optimal power flow problem has been widely studied in order to improve power systems operation and planning. For real power systems, the problem is formulated as a non-linear and as a large combinatorial problem. The first approaches used to solve this problem were based on mathematical methods which required huge computational efforts. Lately, artificial intelligence techniques, such as metaheuristics based on biological processes, were adopted. Metaheuristics require lower computational resources, which is a clear advantage for addressing the problem in large power systems. This paper proposes a methodology to solve optimal power flow on economic dispatch context using a Simulated Annealing algorithm inspired on the cooling temperature process seen in metallurgy. The main contribution of the proposed method is the specific neighborhood generation according to the optimal power flow problem characteristics. The proposed methodology has been tested with IEEE 6 bus and 30 bus networks. The obtained results are compared with other wellknown methodologies presented in the literature, showing the effectiveness of the proposed method.

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To maintain a power system within operation limits, a level ahead planning it is necessary to apply competitive techniques to solve the optimal power flow (OPF). OPF is a non-linear and a large combinatorial problem. The Ant Colony Search (ACS) optimization algorithm is inspired by the organized natural movement of real ants and has been successfully applied to different large combinatorial optimization problems. This paper presents an implementation of Ant Colony optimization to solve the OPF in an economic dispatch context. The proposed methodology has been developed to be used for maintenance and repairing planning with 48 to 24 hours antecipation. The main advantage of this method is its low execution time that allows the use of OPF when a large set of scenarios has to be analyzed. The paper includes a case study using the IEEE 30 bus network. The results are compared with other well-known methodologies presented in the literature.

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Mathematical Program with Complementarity Constraints (MPCC) finds many applications in fields such as engineering design, economic equilibrium and mathematical programming theory itself. A queueing system model resulting from a single signalized intersection regulated by pre-timed control in traffic network is considered. The model is formulated as an MPCC problem. A MATLAB implementation based on an hyperbolic penalty function is used to solve this practical problem, computing the total average waiting time of the vehicles in all queues and the green split allocation. The problem was codified in AMPL.

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This paper studies the optimization of complex-order algorithms for the discrete-time control of linear and nonlinear systems. The fundamentals of fractional systems and genetic algorithms are introduced. Based on these concepts, complexorder control schemes and their implementation are evaluated in the perspective of evolutionary optimization. The results demonstrate not only that complex-order derivatives constitute a valuable alternative for deriving control algorithms, but also the feasibility of the adopted optimization strategy.

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Computational Intelligence (CI) includes four main areas: Evolutionary Computation (genetic algorithms and genetic programming), Swarm Intelligence, Fuzzy Systems and Neural Networks. This article shows how CI techniques overpass the strict limits of Artificial Intelligence field and can help solving real problems from distinct engineering areas: Mechanical, Computer Science and Electrical Engineering.

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This study addresses the optimization of fractional algorithms for the discrete-time control of linear and non-linear systems. The paper starts by analyzing the fundamentals of fractional control systems and genetic algorithms. In a second phase the paper evaluates the problem in an optimization perspective. The results demonstrate the feasibility of the evolutionary strategy and the adaptability to distinct types of systems.

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Atualmente a vantagem competitiva de uma empresa passa pela sua rápida adaptação às variações de procura do mercado, sendo necessário garantir elevados níveis de produtividade e, simultaneamente, grande flexibilidade, indispensável ao fabrico de pequenos lotes. A necessidade de ajuste do processo e a diminuição da média de vida do produto levam a paragens cada vez mais frequentes da célula de fabrico para programação e afinação, com consequentes perdas de produtividade. De forma a dar resposta a estes problemas, neste trabalho é testada a viabilidade da utilização da programação e simulação offline de tarefas de lixamento na Grohe Portugal, complementando a solução com o desenvolvimento de um novo método de afinação do programa, permitindo uma adaptação às flutuações do processo produtivo. Para isso foi necessário analisar o estado da arte dos robôs industriais na área de acabamento superficial e respetivos métodos de programação. Em seguida, após um trabalho prévio rigoroso de preparação e modelação da célula de trabalho, é possível fazer a programação offline das várias rotinas e trajetórias complexas que compõem um ciclo de lixamento de um produto, contribuindo para o aumento da qualidade do produto final sem comprometer os níveis de produtividade. Nesta dissertação são descritos e detalhados alguns dos procedimentos fulcrais no sucesso da aplicação deste método de programação. Por último é feita uma nova abordagem ao método de ajuste ponto-a-ponto convencional, desenvolvendo-se para isso um sistema de ajuste automático do programa, dotando o robô da capacidade de se adaptar às variações do processo, assegurando a consistência do mesmo. Foram realizados testes em pequena escala, extrapolando-se os resultados para a aplicação deste novo método no processo produtivo da Grohe Portugal, como forma de complemento ao método convencional de ajuste ponto-a-ponto do programa, reduzindo o tempo de paragem da célula de trabalho.

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In this paper we propose a novel fully probabilistic solution to the stereo egomotion estimation problem. We extend the notion of probabilistic correspondence to the stereo case which allow us to compute the whole 6D motion information in a probabilistic way. We compare the developed approach against other known state-of-the-art methods for stereo egomotion estimation, and the obtained results compare favorably both for the linear and angular velocities estimation.

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This article presents a novel method for visualizing the control systems behavior. The proposed scheme uses the tools of fractional calculus and computes the signals propagating within the system structure as a time/frequency-space wave. Linear and nonlinear closed-loop control systems are analyzed, for both the time and frequency responses, under the action of a reference step input signal. Several nonlinearities, namely, Coulomb friction and backlash, are also tested. The numerical experiments demonstrate the feasibility of the proposed methodology as a visualization tool and motivate its extension for other systems and classes of nonlinearities.

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Este trabalho pretende estabelecer uma relação entre o Work Index e algumas propriedades das rochas. Através da pesquisa bibliográfica foram identificadas varias propriedades com possível influência no valor do Work Index, das quais foram seleccionadas a massa volúmica aparente, a resistência à carga pontual, a composição química, a composição mineralógica e a abrasividade. Adicionalmente a porosidade aberta e resistência à compressão também foram analisadas. Assim foram analisadas 10 amostras de rocha, quatro de granitos, uma de quartzodiorito, uma de ardósia, uma de serpentinito, uma de calcário, uma de mármore e uma de sienito nefelínico, sobre as quais já eram conhecidos os valores de cinco das propriedades referidas previamente, tendo sido determinados os valores das ainda desconhecidas, resistência à carga pontual e a abrasividade que está representada através do resultado do ensaio capon. Devido à dificuldade de execução do ensaio de determinação do Work Index de Bond foram recolhidos dados bibliográficos de valores do Work Index para as amostras de rocha seleccionadas e adoptado o valor médio para cada uma. Os dados obtidos foram tratados estatisticamente através do método de análise de componentes principais assim como através de regressões lineares simples e múltiplas. A análise de componentes principais permitiu identificar várias propriedades da rocha com possível influência sobre o Work Index de entre as analisadas. Foi possível estabelecer uma relação entre o Work Index e quatro das propriedades seleccionadas, designadamente a porosidade aberta, a resistência à compressão, a resistência à carga pontual e a abrasividade.