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Elismar R. Oliveira

Publications and source records attributed to Elismar R. Oliveira.

At least 19 recordsLinked to original sources

Most A$_α$-eigenvalues of a tree are small

We study the distribution of $A_α$-eigenvalues of a tree. We extend the works \cite{Jacobs2021} and \cite{SIN2020} by proving that the number of $A_α$-eigenvalues, for $0\leq α\leq \frac{1}{2}$, less than or equal to the average degree $d_α= α(2- 2/n)$ is, at least, $\lceil \frac{n}{2} \rceil$ for a tree with $n$ vertices. Several counterexamples for $\frac{1}{2} < α\leq 1$ are exhibited. We also derive the same result for other well-known families such as the Deformed Laplacian and the matrix $B_β$.

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Stability Theory for Local Iterated Function Systems

We develop a stability theory for contractive local IFSs on compact metric spaces. Unlike the classical global setting, local systems may exhibit a richer symbolic and geometric structure, including code spaces that are not of finite type and attractors with endpoints, leading to new mechanisms of instability. We first prove that concordant shadowing implies upper semicontinuity of the local attractor and persistence of the code space, yielding a criterion for combinatorial stability under perturbations. Under the open set condition, we establish a strong form of topological stability for combinatorially stable contractive local systems, and prove the converse implication on compact manifolds of dimension at least three. In particular, we show that contractive graph-directed IFSs are topologically stable. We also construct contractive local IFSs derived from beta-transformations that are combinatorially unstable. These results show that stability in the local setting is governed by the interplay between contraction and the combinatorial rigidity of the code space. Applications to graph-directed IFSs and pseudogroup actions are also given.

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Foundations of local iterated function systems

In this paper we present a systematic study of continuous local iterated function systems. We prove local iterated function systems admit compact attractors and, under a contractivity assumption, construct their code space and present an extended shift that describes admissible compositions. In particular, the possible combinatorial structure of a local iterated function system is in bijection with the space of invariant subsets of the full shift. Nevertheless, these objects reveal a degree of unexpectedness relative to the classical framework, as we build examples of local iterated function systems which are not modeled by subshifts of finite type and give rise to non self-similar attractors. We also prove that all attractors of graph-directed IFSs are obtained from local IFSs on an enriched compact metric space. We provide several classes of examples illustrating the scope of our results, emphasizing both their contrasts and connections with the classical theory of iterated function systems.

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Distribution of deformed Laplacian limit points

This paper investigates limit points of the deformed Laplacian matrix, which merges the Laplacian and signless Laplacian matrices of a graph through a quadractic one-parameter family of matrices. First, we show that any value greater or equal to 1 is a deformed Laplacian limit point (for different values of the parameter $s$) using a simple family of trees. Second, we define $(T_k)_{k \in \mathbb{N}}$ the Shearer's sequence of caterpillars for $λ>1$ and we present a convergence criterion based on Shearer's approach. Our main result is that for any fixed value $λ_0>1$ there exists a unique value $0<s^* <\sqrt{λ_0} -1$ such that, and for any $s \in (0,s^*)$ the interval $[λ_0, \; +\infty)$ is entirely formed by $s$-deformed Laplacian limit points (for the same value of $s$). Finally, we provide some numerical data exploring the limit properties.

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Spectral properties of the deformed Laplacian matrix of trees and H-join graphs

This paper investigates spectral properties of the deformed Laplacian matrix, which merges the Laplacian and signless Laplacian matrices of a graph through a one-parameter family of matrices. We present general results on the eigenvalues of these matrices for simple undirected graphs. Additionally, we analyze the spectrum of the deformed Laplacian in the specific cases of trees and H-join graphs. For trees, we derive strong results on the localization of eigenvalues, while for H-join graphs, we explicitly compute the spectrum of the deformed Laplacian.

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Blending attractors of Iterated Function Systems

In this paper we discuss a new method to blend fractal attractors using the code map for the IFS formed by the Hutchinson--Barnsley operators of a finite family of hyperbolic IFSs. We introduce a parameter called blending coefficient to measure the similarity between the blended set and each one of the original attractors. We also introduce a discrete approximation algorithm and prove a rigorous error estimation used to approximate these new objects. Several simulation results are provided illustrating our techniques.

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The Hutchinson-Barnsley theory for iterated function systems with general measures

In this work we present iterated function systems with general measures(IFSm) formed by a set of maps $τ_λ$ acting over a compact space $X$, for a compact space of indices, $Λ$. The Markov process $Z_k$ associated to the IFS iteration is defined using a general family of probabilities measures $q_x$ on $Λ$, where $x \in X$: $Z_{k+1}$ is given by $τ_λ(Z_k)$, with $λ$ randomly chosen according to $q_x$. We prove the existence of the topological attractor and the existence of the invariant attracting measure for the Markov Process. We also prove that the support of the invariant measure is given by the attractor and results on the stochastic stability of the invariant measures, with respect to changes in the family $q_x$.

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On the Higuchi fractal dimension of invariant measures for countable idempotent iterated function systems

We investigate the set of invariant idempotent probabilities for countable idempotent iterated function systems (IFS) defined in compact metric spaces. We demonstrate that, with constant weights, there exists a unique invariant idempotent probability. Utilizing Secelean's approach to countable IFSs, we introduce partially finite idempotent IFSs and prove that the sequence of invariant idempotent measures for these systems converges to the invariant measure of the original countable IFS. We then apply these results to approximate such measures with discrete systems, producing, in the one-dimensional case, data series whose Higuchi fractal dimension can be calculated. Finally, we provide numerical approximations for two-dimensional cases and discuss the application of generalized Higuchi dimensions in these scenarios.

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Thermodynamic Formalism for a family of cellular automata and duality with the shift

We will consider a family of cellular automata $Φ: \{1,2,...,r\}^\mathbb{N}\circlearrowright$ that are not of algebraic type. Our first goal is to determine conditions that result in the identification of probabilities that are at the same time $σ$-invariant and $Φ$-invariant, where $σ$ is the full shift. Via the use of versions of the Ruelle operator $\mathcal{L}_{A,σ}$ and $\mathcal{L}_{B,Φ}$ we will show that there is an abundant set of measures with this property; they will be equilibrium probabilities for different Lispchitz potentials $A,B$ and for the corresponding dynamics $σ$ and $Φ$. Via the use of a version of the involution kernel $W$ for a $(σ,Φ)$-mixed skew product $\hatΦ: \{1,2,...,r\}^\mathbb{Z}\circlearrowright$, given $A$ one can determine $B$, in such way that the integral kernel $e^W$ produce a duality between eigenprobabilities $ρ_A$ for $(\mathcal{L}_{A,σ})^*$ and eigenfunctions $ψ_B$ for $\mathcal{L}_{B,Φ}$. In another direction, considering the non-mixed extension $\hatΦ_n : \{1,2,...,r\}^\mathbb{Z}\circlearrowright$ of $Φ$, given a Lispchitz potential $\hat{A} : \{1,2,...,r\}^\mathbb{Z}\to \mathbb{R}$, we can identify a Lipschitz potential $A:\{1,2,...,r\}^\mathbb{N} \to \mathbb{R} $, in such away that relates the variational problem of $\hatΦ_n$-Topological Pressure for $\hat{A}$ with the $Φ$-Topological Pressure for $A$. We also present a version of Livsic's Theorem. Whether or not $Φ$ (or $\hatΦ)$ can eventually be conjugated with another shift of finite type is irrelevant in our context.

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Large deviation for Gibbs probabilities at zero temperature and invariant idempotent probabilities for iterated function systems

We consider two compact metric spaces $J$ and $X$ and a uniform contractible iterated function system $\{ϕ_j: X \to X \, | \, j \in J \}$. For a Lipschitz continuous function $A$ on $J \times X$ and for each $β>0$ we consider the Gibbs probability $ρ_{_{βA}}$. Our goal is to study a large deviation principle for such family of probabilities as $β\to +\infty$ and its connections with idempotent probabilities. In the non-place dependent case ($A(j,x)=A_j,\,\forall x\in X$) we will prove that $(ρ_{_{βA}})$ satisfy a LDP and $-I$ (where $I$ is the deviation function) is the density of the unique invariant idempotent probability for a mpIFS associated to $A$. In the place dependent case, we prove that, if $(ρ_{_{βA}})$ satisfy a LDP, then $-I$ is the density of an invariant idempotent probability. Such idempotent probabilities were recently characterized through the Mañé potential and Aubry set, therefore we will obtain an identical characterization for $-I$.

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Limit points of (signless) Laplacian spectral radii of linear trees

We study limit points of the spectral radii of Laplacian matrices of graphs. We adapted the method used by J. B. Shearer in 1989, devised to prove the density of adjacency limit points of caterpillars, to Laplacian limit points. We show that this fails, in the sense that there is an interval for which the method produces no limit points. Then we generalize the method to Laplacian limit points of linear trees and prove that it generates a larger set of limit points. The results of this manuscript may provide important tools for proving the density of Laplacian limit points in $[4.38+, \infty)$.

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Invariant measures for place dependent idempotent iterated function systems

We study the set of invariant idempotent probabilities for place dependent idempotent iterated function systems defined in compact metric spaces. Using well-known ideas from dynamical systems, such as the Mañé potential and the Aubry set, we provide a complete characterization of the densities of such idempotent probabilities. As an application, we provide an alternative formula for the attractor of a class of fuzzy iterated function systems.

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Limit points of $A_α$-matrices of graphs

We study limit points of the spectral radii of $A_α$-matrices of graphs. Adapting a method used by J. B. Shearer in 1989, we prove a density property of $A_α$-limit points of caterpillars for $α$ close to zero. Precisely, we show that for $α\in [0, 1/2)$ there exists a positive number $τ_2(α)>2$ such that any value $λ> τ_2(α)$ is an $A_α$-limit point. We also determine the existence of other intervals for which all its points are $A_α$-limit points.

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The Hutchinson-Barnsley theory for generalized iterated function systems by means of infinite iterated function systems

The study of generalized iterated function systems (GIFS) was introduced by Mihail and Miculescu in 2008. We provide a new approach to study those systems as the limit of the Hutchinson-Barnsley setting for infinite iterated function systems (IIFS) which has been developed by many authors in the last years. We show that any attractor of a contractive generalized iterated function system is the limit with respect to Hausdorff-Pompeiu metric of attractors of contractive infinite iterated function systems. We also prove that any Hutchinson measure for a contractive generalized iterated function system with probabilities is the limit with respect to the Monge-Kantorovich metric of the Hutchinson measures for contractive infinite iterated function systems with probabilities.

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Thermodynamic formalism for general iterated function systems with measures

This paper introduces a theory of Thermodynamic Formalism for Iterated Function Systems with Measures (IFSm). We study the spectral properties of the Transfer and Markov operators associated to a IFSm. We introduce variational formulations for the topological entropy of holonomic measures and the topological pressure of IFSm given by a potential. A definition of equilibrium state is then natural and we prove its existence for any continuous potential. We show, in this setting, a uniqueness result for the equilibrium state requiring only the Gâteaux differentiability of the pressure functional.

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On I-eigenvalue free threshold graphs

A graph is said to be I-eigenvalue free if it has no eigenvalues in the interval I with respect to the adjacency matrix A. In this paper we present two algorithms for generating I-eigenvalue free threshold graphs.

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