Recursos de colección

Estudo Geral - Universidade de Coimbra (19.630 recursos)

ESTUDO GERAL é a designação do repositório digital da produção científica da Universidade de Coimbra, com o objectivo de divulgar conteúdos digitais de natureza científica de autores ligados à Universidade de Coimbra. A sua criação insere-se no movimento de Acesso Livre à Literatura científica (Open Access), ao qual o Conselho de Reitores das Universidades Portuguesas aderiu em 2006 e que a Universidade de Coimbra subscreveu. À semelhança de outras grandes universidades nacionais e internacionais, a UC tem o maior interesse em aumentar a sua presença na rede informática mundial, sendo cada vez mais - e também por essa via - um emissor de conhecimento e cultura.

FCTUC Matemática - Artigos em Revistas Nacionais

Mostrando recursos 1 - 20 de 120

  1. A new improvement for a K shortest paths algorithm

    Martins, Ernesto de Queirós Vieira; Pascoal, Marta Madalena Braz; Santos, José Luís Esteves

  2. Aplicação do algoritmo volumétrico na resolução aproximada e exacta do problema do caixeiro viajante assimétrico

    Rocha, Ana Maria; Fernandes, Edite M. G. P.; Soares, João
    Neste artigo apresentamos resultados computacionais obtidos com o algoritmo volumétrico, uma variante do método do subgradiente, na resolução da relaxação linear que decorre da formulação estendida de fluxo desagregado para o problema do Caixeiro Viajante Assimétrico. As experiências computacionais foram realizadas numa selecção de instâncias da TSPLib e num conjunto de instâncias geradas aleatoriamente de acordo com o Dimacs Implementation Challenge. Também experimentámos a aplicação de heurísticas durante a execução do algoritmo volumétrico. As experiências computacionais mostram sucesso moderado com instâncias de média dimensão.

  3. Um melhor limite inferior para o problema do caixeiro viajante assimétrico baseado no problema da afectação

    Ramires, Ana; Soares, João
    Neste artigo explicamos como obter um limite inferior para o valor óptimo do problema do caixeiro viajante assimétrico melhor do que o que advém do problema de afectação através da resolução sucessiva de problemas de afectação. O algoritmo que propomos é um método de primeira ordem baseado na função de penalidade exponencial cujas direcções de deslocamento são definidas com base numa relaxação disjuntiva que propomos ser de dois tipos, uma baseada em ciclos e a outra baseada em cliques.

  4. On computing real logarithms for matrices in the Lie group of special Euclidean motions in Rn

    Cardoso, J. R.; Leite, F. Silva
    We show that the diagonal Pade approximants methods, both for computing the principal logarithm of matrices belonging to the Lie groupSE (n, IR) of special Euclidean motions in IRn and to compute the matrix exponential of elements in the corresponding Lie algebra se(n, IR), are structure preserving. Also, for the particular cases when n == 2,3 we present an alternative closed form to compute the principal logarithm. These low dimensional Lie groups play an important role in the kinematic motion of many mechanical systems and, for that reason, the results presented here have immediate applications in robotics

  5. Covariance estimator for associated random variables

    Henriques, Carla; Oliveira, Paulo Eduardo
    Considering an associated and strictly stationary sequence of random variables we introduce an histogram estimator for the covariances between indicator functions of those random variables. We find conditions on the covariance structure of the original random variables for the almost sure convergence of the estimator and for the convergence in distribution of the finite dimensional distributions. Finally we characterize the usual error criteria finding their convergence rates under assumptions on the convergence rate of the covariances

  6. On indicatrices

    Carvalho, F. J. Craveiro de

  7. On decompositions in generalised Lorentz-Zygmund spaces

    Neves, J. S.

  8. Finite preorders and topological descent

    Janelidze, George; Sobral, Manuela
    It is shown that the descent constructions of finite preorders provide a simple motivation for those of topological spaces, and new counter-examples to open problems in Topological descent theory are constructed

  9. Asymptotic separation in bilinear models

    Gonçalves, E.; Martins, C. M.; Mendes-Lopes, N.
    This paper presents a generalisation of a non classical decision procedure for simple bilinear models with a general error process proposed by Gon calves Jacob and Mendes Lopes This decision method involves two hypotheses on the model and its consis tence is obtained by establishing the asymptotic separation of the sequences of probability laws de ned by each hypothesis Studies on the rate of convergence in the diagonal case are presented and an exponential decay is obtained Simulation experiments are used to illustrate the behaviour of the power and level functions in small and moderate samples when this procedure is used as a test

  10. About fitted finite-difference operators and fitted meshes for solving singularly perturbed linear problems in one dimension

    Oliveira, F. Aragão
    Classical finite-difference operators on uniform meshes are not appropriate for solving singularly perturbed differential equations due to the effect of the boundary layers.If we want uniformly convergent difference schemes (with respect to some discrete norm), we need to adequate the numerical operator or the mesh, or both, the operator and the mesh. We summarize some recent results about uniform convergent methods for a general linear two point boundary value problem and present two algorithms related with the numerical method, which give indication about the transition points of the solution in the given domain. They are transition point indicators

  11. L-splines - A manifestation of optimal control

    Rodrigues, Rui C.; Leite, F. Silva
    We show how to generate a class of Euclidean splines, called L-splines, as solutions of a high-order variational problem. We also show connections between L-splines and optimal control theory, leading to the conclusion that L-splines are manifestations of an optimal behavior

  12. Hölder continuity of local weak solutions for parabolic equations exhibiting two degeneracies

    Urbano, José Miguel
    We consider equations of the form atv - div(Q ( v)Vv) == 0 , where v E [0,1] and Q(v) degenerates for v == 0 and v == 1. We show that local weak solutions are locally Holder continuous provided Q behaves like a power near the two degeneracies. We adopt the technique of intrinsic rescaling developed by DiBenedetto.

  13. Histogram estimation of Radon-Nikodym derivatives for strong mixing data

    Bensaïd, Nadia; Oliveira, Paulo Eduardo
    Nonparametric inference for point processes is discussed by way histograms, which provide a nice tool for the analysis of on-line data. The construction of histograms depends on a sequence of partitions, which we take to be nonembedded to allow partitions with sets of equal measure. This presents some theoretical problems, which are addressed with an assumption on the decomposition of second order moments. In another direction, we drop the usual independence assumption on the sample, replacing it by a strong mixing assumption. Under this setting, we study the convergence of the histogram in probability, which depends on approximation conditions between the distributions of random pairs and the...

  14. Algebraically linearizable dynamical systems

    Caseiro, R.; Françoise, J. P.
    The main result of this paper is the evidence of an explicit linearization of dynamical systems of Ruijsenaars-Schneider (RS) type and of the perturbations introduced by F. Calogero of these systems with all orbits periodic of same period. Several other systems share the existence of this explicit linearization, among them, the Calogero-Moser system (with and without external potential) and the Calogero-Sutherland system. This explicit linearization is compared with the notion of maximal superintegrability which has been discussed in several articles (to quote few of them, Hietarinta [12], Henon [11], Harnad-Winternitz [10], S. Wojchiechowsky [15]).

  15. On coregular closure operators

    Gutierres, Gonçalo
    Among closure operators in the sense of Dikranjan and Giuli [5] the regular ones have a relevant role and have been widely investigated. On the contrary, the coregular closure operators were introduced only recently in [3] and they need to be further investigated. In this paper we study co regular closure operators, in connection connectednesses and disconnectednesses, in the realm of topological spaces and modules.

  16. Some remarks on the Poisson-Nijenhuis and the Jacobi structures

    Costa, J. M. Nunes da
    We study the relationship between two (compatible) J acobi structures on a manifold M, using their associated homogeneous Poisson structures on lR x M, in the case where these Poisson tensors are related by a Nijenhuis tensor.

  17. A singular-degenerate parabolic problem: regularity up to the Dirichlet boundary

    Urbano, José Miguel
    We show that weak solutions of a free boundary problem, modeling a waterice phase transition in the case of nonlinear heat diffusion, are continuous up to the lateral boundary. We consider homogeneous Dirichlet boundary conditions and assume that the lateral boundary of the space-time domain satisfies the property of positive geometric density. The results are a follow up from recent results by the author concerning the interior regularity.

  18. Locally Sierpinski Quotients of the Sorgenfrey Line

    Carvalho, F. J. Craveiro de

  19. A Free Boundary Problem: contributions from modern analysis

    Urbano, José Miguel
    We exemplify the role of Free Boundary Problems as an important source of ideas in modern analysis. With the help of a model problem we illustrate the use of analytical, algebraic and geometrical techniques obtaining uniqueness of weak solutions via the use of entropy inequalities, existence through nonlinear semigroup theory, and regularity using a method, called intrinsic scaling, based on interpreting a partial differential equation in a geometry dictated by its own structure

  20. Complementarity and genetic algorithms for an optimization shell problem

    Figueiredo, Isabel N.; Júdice, Joaquim J.; Oliveira, Pedro N.
    The application of complementarity and genetic algorithms to an optimization thin laminated shallow shell problem is discussed. The discrete form of the problem leads to a Mathematical Program with Equilibrium Constraints (MPEC) [1], whose constraint set consists of a variational inequality and a set of equality constraints. Furthermore the variables are discrete. Special instances of the general problem are considered and indicate that the choice of the algorithm depends on the problem to be linear or nonlinear.

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