11/2018 |
On Space Maximal Curves Paulo César Oliveira, Fernando Torres Any maximal curve X is equipped with an intrinsic embedding π : X → Pr which reveal outstanding properties of the curve. By dealing with the contact divisors of the curve π(X) and tangent lines, in this paper we investigate the ﬁrst positive element that the Weierstrass semigroup at rational points can have whenever r = 3 and π(X) is contained in a cubic surface. rp-2018-11.pdf |

10/2018 |
Locally Recoverable Codes From Algebraic Curves with Separated Variables Carlos Munuera, Wanderson Tenório, Fernando Torres A Locally Recoverable code is an error-correcting code such that any erasure in a single coordinate of a codeword can be recovered from a small subset of other coordinates. We study Locally Recoverable Algebraic Geometry codes arising from certain curves deﬁned by equations with separated variables. The recovery of erasures is obtained by means of Lagrangian interpolation in general, and simply by one addition in some particular cases. rp-2018-10.pdf |

9/2018 |
The Multivariate Birnbaum-Saunders Distribution Based on a Asymmetric Distribution: EM-Estimation Filidor Vilca, Camila Borelli Zeller, N. Balakrishnan We derive here a multivariate generalization of the bivariate Birnbaum-Saunders (BS) distribution of Kundu et al. (2010) by basing it on the multivariate skew-normal (SN) distribution. The resulting multivariate Birnbaum-Saunders type distribution is an absolutely continuous distribution whose marginals are in the form of univariate Birnbaum-Saunders type distributions discussed by Vilca et al. (2011). We then study its characteristics and properties, such as the joint distribution function, marginal and conditional distributions. Next, we introduce a non-central multivariate BS distribution in order to present analytically a simple EM-algorithm for iteratively computing the maximum likelihood estimates of the model parameters, and compare the performance of this method with the estimation approach of Jamalizadeh and Kundu (2015). Moreover, the observed Fisher information matrix is analytically derived under the bivariate case, and some simulation studies and an application to a real data set are ﬁnally presented for the propose of illustrating the model and inferential results developed here. rp-2018-09.pdf |

8/2018 |
Estimates for Entropy Numbers of Sets of Smooth Functions on the Torus Td R. L. B. Stabile, S. A. Tozoni In this paper, we investigate entropy numbers of multiplier operators of functions defined on the d-dimensional torus. In the first part, upper and lower bounds are established for entropy numbers of general multiplier operators bounded from Lp to Lq. In the second part, we apply these results to study entropy numbers of sets of finitely differentiable functions, in particular Sobolev classes, and sets of infinitely differentiable and analytic functions, on the d-dimensional torus. We prove that, the estimates for the entropy numbers are order sharp in various important situations. rp-2018-08.pdf |

7/2018 |
A log Birnbaum-Saunders regression model based on the skew-normal distribution under the centred parameterization Nathalia L. Chaves, Caio L. N. Azevedo, Filidor Vilca-Labra, Juvêncio S. Nobre In this paper, we introduce a new regression model for positive and skewed data, a log Birnbaum-Saunders model based on the centred skew-normal distribution, and we present a several inference tools for this model. Initially, we developed a new version of skew-sinh-normal distribution and we describe some of its properties. For the proposed regression model, we carry out, through of the expectation conditional maximization (ECM) algorithm, the parameter estimation, model fit assessment, model comparison and residual analysis. Finally, our model accommodates more suitably the asymmetry of the data, compared with the usual log Birnbaum-Saunders model, which is illustrated through real data analysis. rp-2018-07.pdf |

6/2018 |
A new Birnbaum-Saunders model based on the skew-normal distribution under the centred parameterization Nathalia L. Chaves, Caio L. N. Azevedo, Filidor Vilca-Labra, Juvêncio S. Nobre In this paper we introduce a new distribution for positive and skewed data by combining the Birnbaum-Saunders (BS) distribution and the centred skew-normal distribution. Several of its properties are developed. Our model accommodates both positively and negatively skewed positive data. Also, we show that our model circumvents some problems related to another BS distribution, based on the skew-normal distribution under the direct parameterization, previously presented in the literature. We developed both maximum likelihood (ML) and Bayesian estimation procedures, comparing them through a suitable simulation study. The convergence of the expectation conditional maximization (ECM) (for ML inference) and MCMC algorithms (for Bayesian inference) were veried and several factors of interest were compared in the parameter recovery study. In general, as the sample size increases, the results indicated that the Bayesian approach provided the most accurate estimates. Finally, our model accommodates the asymmetry of the data, compared with the usual BS model, which is illustrated through real data analysis. rp-2018-06.pdf |

5/2018 |
Optimal Approximation by sk-Splines on the Torus J. G. Oliveira, S. A. Tozoni Fixed a continuous kernel rp-2018-5.pdf |

4/2018 |
On the Ree Curve Saeed Tafazolian, Fernando Torres We point out a characterization of the Ree curve which involves the number of rational points, the genus, and the shape of two elements of the Weierstrass semigroup at a rational point. rp-2018-042018.pdf |

3/2018 |
Limit Cycles Bifurcating From Discontinuous Polynomial Pertubations of Higher Dimensional Linear Differential Systems Jaume Llibre, Douglas D. Novaes, Iris O. Zeli We study the periodic solutions bifurcating from periodic orbits of linear differential systems x0 = Mx, when they are perturbed inside a class of discontinuous piecewise polynomial differential systems with two zones. More precisely, we study the periodic solutions of the differential system x0 = Mx + "F n 1 (x) + "2Fn2 (x); rp-2018-03.pdf |

2/2018 |
Normal Forms of Bireversible Vector Fields P. H. Baptistelli, M. Manoel, I.O. Zeli In this paper we adapt the method of [P. H. Baptistelli, M. Manoel and I. O. Zeli. Normal form theory for reversible equivariant vector elds. Bull. Braz. Math. Soc., New Series 47 (2016), no. 3, 935-954] to obtain normal forms of a class of smooth bireversible vector elds. These are vector elds reversible under the action of two linear involution and whose linearization has a nilpotent part and a semisimple part with purely imaginary eigenvalues. We show that these can be put formally in normal form preserving the reversing symmetries and their linearization. The approach we use is based on an algebraic structure of the set of this type of vector elds. Although this can lead to extensive rp-2018-02.pdf |

A Biblioteca do IMECC faz parte de um contexto de expressiva produção do instituto. Conheça nossos números.

Responsável pelas informações nesta página: