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C. A. Morales

Publications and source records attributed to C. A. Morales.

At least 19 recordsLinked to original sources
arXiv2026

Topological Expansivity and Shadowing for Anosov Diffeomorphisms

We show that every Anosov diffeomorphism is topologically expansive in the sense of [9]. We also prove that Lipschitz shadowing forces the stable and unstable bundles to be uniformly transverse, with a quantitative bound in terms of the shadowing constant. Finally, we give two examples on complete Riemannian manifolds: one is expansive but does not have the shadowing property, while the other has finite volume, bounded sectional curvature, Lipschitz shadowing, and orthogonal invariant bundles, but is not expansive with respect to its Riemannian distance.

math.DS↗
arXiv2026

Entropy on regular sets and periodic-orbit growth for singular flows

We study entropy and periodic-orbit growth for flows on metric spaces. First, we prove that the finite topological entropy of a flow on a compact metric space is completely carried by compact subsets of its regular set. Next, we establish a Bowen--Walters inequality for geometrically separating flows on possibly noncompact metric spaces, under uniform control at time zero and dynamical isolation at infinity. As applications, we obtain the Bowen--Walters inequality for singular suspension flows over expansive homeomorphisms, multisingular-hyperbolic sets---extending the upper-bound part of \cite{pyyz}---and asymptotically sectional-hyperbolic attractors such as Rovella's \cite{r}.

math.DS↗
arXiv2026

At most exponential growth of periodic orbits for star flows

We prove that on any closed manifold there exists a C1 open and dense subset of star flows for which the periodic orbits grow at most expo- nentially. We also explain how our methods apply to the sectional-hyperbolic attractors including the Lorenz polynomial equation.

math.DS↗
arXiv2026

Topological shadowing for linear operators

We prove a linear operator of a finite-dimensional Banach space has the topological shadowing property, as introduced in \cite{lny}, if and only if its spectrum lies either within the open unit complex disk or outside the closure of that disk. Moreover, the spectrum of every uniformly expansive linear operator with the topological shadowing property lies either within the open unit complex disk or outside the closure of that disk. Lastly, we prove that a normal operator with the topological shadowing property on a Hilbert space does not have any nonzero nonwandering points.

math.FA↗
arXiv2026

Robust transitivity without sectional-hyperbolicity

For any integer $n \geq 5$, we construct an $n$-dimensional $C^1$ vector field exhibiting a robustly transitive singular attractor which is not sectional-hyperbolic. Nevertheless, the attractor is singular-hyperbolic. This provides the first such examples improving some features of the constructions in [17, 32].

math.DS↗
arXiv2025

Topological stability from a measurable viewpoint

We introduce the {\em $μ$-topological stability}. This is a type of stability depending on the measure $μ$ different from the set-valued approach \cite{lm}. We prove that the map $f$ is $m_p$-topologically stable if and only if $p$ is a topologically stable point ($m_p$ is the Dirac measure supported on $p$). On closed manifolds of dimension $\geq2$ we prove that every $μ$-topologically stable map has the $μ$-shadowing property for finitely supported measures $μ$. Moreover the $μ$-topological stability is invariant under topological conjugacy or restriction to compact invariant sets of full measure. We also prove for expansive maps that the set of measures $μ$ for which the map is $μ$-topologically stable is convex. We analyze the relationship between $μ$-topological stability for absolutely continuous measures. In the nonatomic case we show that the $μ$-topological stability implies the set-valued stability approach in \cite{lm}. Finally, we show that every expansive map with the weak $μ$-shadowing property (c.f. \cite{lr}) is $μ$-topologically stable.

math.DS↗
arXiv2025

Characterizing expansivity through $C^*$-algebras

We study expansive homeomorphisms of a compact metric space $X$ through the lens of the commutative $C^*$-algebra $C(X)$ of continuous complex-valued functions, viewed as observables of the system. We introduce the notion of expansive observables: elements of $C(X)$ whose level sets distinguish distinct orbits. We prove that the expansive observables form an F$_σ$-subalgebra of $C(X)$, and we characterize them completely for connected equicontinuous homeomorphisms, showing that only constant observables are expansive in this setting. Furthermore, we establish that topologically conjugate homeomorphisms share the same algebra of expansive observables. Using this framework, we show that the set of periodic points intersects at most countably many level sets of any expansive observable. This provides $C^*$-algebraic proofs of well-known facts like for instance that the set of periodic points of an expansive homeomorphism is countable or that the sole continuum exhibiting homeomorphisms which are both expansive and equicontinuous are the degenerated ones. Finally, we prove that no homeomorphism of the circle or the unit interval admits a dense set of expansive observables, yielding a $C^*$-algebraic demonstration of the nonexistence of expansive homeomorphisms in these spaces.

math.DS↗
arXiv2025

Expansiveness for flows on noncompact spaces

We introduce the concept of topological expansive flow. We prove that this concept is invariant by topological conjugacy and reduces to expansivity in the compact case. We characterize tiopological expansive flows as rescaling expansive flows for which the singularities are isolated points of the space. Finally, we prove that the growth rate of the periodic orbits of a topological expansive flow which is dynamically isolated at infinity is controlled by an entropy-like invariant. This extends Bowen-Walters inequality for expansive flows on compact spaces.

math.DS↗
arXiv2025

On the plaque topological stability of partially hyperbolic diffeomorphisms

We prove that every dynamically coherent plaque expansive partially hyperbolic diffeomorphism is topologically stable with respect to the central foliation (in short, {\em plaque topologically stable}). Next, we study partially hyperbolic diffeomorphisms that are both expansive and topologically stable with respect to a central foliation. We show that the center chain recurrent set for such diffeomorphisms belongs to the closure of the center periodic points.

math.DS↗
arXiv2025

A measure-theoretic expansion exponent

The expansion exponent (or expansion constant) for maps was introduced by Schreiber in \cite{s}. In this paper, we introduce the analogous exponent for measures. We shall prove the following results: The expansion exponent of a measurable maps is equal to the minimum of the expansion exponent taken over the Borel probability measures. In particular, a map expands small distances (in the sense of Reddy \cite{r}) if and only if every Borel probability has positive expansion exponent. Any nonatomic invariant measure with positive expansion exponent is positively expansive in the sense of \cite{m}. For ergodic invariant measures, the Kolmogorov-Sinai entropy is bounded below by the product of the expansion exponent and the measure upper capacity. As a consequence, any ergodic invariant measure with both positive upper capacity and positive expansion exponent must have positive entropy.

math.DS↗
arXiv2025

Measure-expansive systems

We call a dynamical system on a measurable metric space {\em measure-expansive} if the probability of two orbits remain close each other for all time is negligible (i.e. zero). We extend results of expansive systems on compact metric spaces to the measure-expansive context. For instance, the measure-expansive homeomorphisms are characterized as those homeomorphisms $f$ for which the diagonal is almost invariant for $f\times f$ with respect to the product measure. In addition, the set of points with converging semi-orbits for such homeomorphisms have measure zero. In particular, the set of periodic orbits for these homeomorphisms is also of measure zero. We also prove that there are no measure-expansive homeomorphisms in the interval and, in the circle, they are the Denjoy ones. As an application we obtain probabilistic proofs of some result of expansive systems. We also present some analogous results for continuous maps.

math.DS↗
arXiv2025

On the universal approximation of real functions with varying domain

We establish sufficient conditions for the density of shallow neural networks \cite{C89} on the family of continuous real functions defined on a compact metric space, taking into account variations in the function domains. For this we use the Gromov-Hausdorff distance defined in \cite{5G}.

math.GN↗
arXiv2024

L-shadowing lemma for the Cauchy equation

We prove that if the Cauchy problem $\dot{u}=Au$ in a Banach space is hyperbolic, then the problem has the L-shadowing property. Conversely, if the space is finite-dimensional and the L-shadowing property is satisfied, then the problem is hyperbolic. This generalizes a previous result by Ombach \cite{o, o1} for linear homeomorphisms. Some short applications are given.

math.AP↗
arXiv2023

Some remarks on projectile motion with a linear resistance force

In this article we revisit the projectile motion assuming a retarding force proportional to the velocity, $\vec{F_r} = -mk\vec{V}$. We obtain an analytical expression for the set of maxima of the trajectories, in Cartesian coordinates, without using the Lambert $W$ function. Also, we investigate the effect of the parameter $k$ on the radial distance of the projectile showing that the radial distance oscillates from a certain critical launch angle and find an approximate expression for it. In our analysis, we consider the impact of the parameter $k$ in the kinetic energy, the potential energy, the total energy and the rate of energy loss, and in the phase space. Our results can be included in an intermediate-level classical mechanics course.

physics.ed-ph↗
arXiv2016

On supports of expansive measures

We prove that a homeomorphism of a compact metric space has an expansive measure \cite{ms} if and only if it has many ones with invariant support. We also study homeomorphisms for which the expansive measures are dense in the space of Borel probability measures. It is proved that these homeomorphisms exhibit a dense set of Borel probability measures which are expansive with full support. Therefore, their sets of heteroclinic points has no interior and the spaces supporting them have no isolated points.

math.DS↗
arXiv2015

Pseudoconnections and Ricci flow

In this note we explain how a flow in the space of Riemmanian metrics (including Ricci's \cite{mt}) induces one in the space of pseudoconnections.

math.DG↗