arXiv subjects

T. Jordão

Publications and source records attributed to T. Jordão.

5 recordsLinked to original sources

arXiv2025

Asymptotic analysis on a non-standard Hilbert space of non-absolutely integrable functions

In this work, we study the Kuelbs-Steadman-2 space (KS-2 space), a Hilbert space constructed via the Henstock-Kurzweil integral, which allows handling non-absolutely integrable functions. We present the construction of the KS-2 space over measurable subsets of $\mathbb{R}^d$ and explore its functional properties with particular focus on integral operators associated with symmetric kernels. A Mercer-type representation theorem is established for such kernels in a KS-2 space, leading to the characterization of the associated Reproducing Kernel Hilbert Spaces (RKHS). As an application, we derive asymptotic upper and lower bounds for the covering numbers of the embedding of the RKHS into the KS-2 space, highlighting how the Fourier coefficients decay rate of the kernels influences the estimates.

math.FA↗

arXiv2023

A close look at the entropy numbers of the unit ball of the Reproducing Hilbert Space of isotropic positive definite kernels

We present accurate upper and lower bounds for the covering numbers, with explicit constants, of the unit ball for two general classes of Reproducing Kernel Hilbert Space (RKHS) on the unit sphere of $\mathbb{R}^{d+1}$. In both classes, the RKHS is generated by an isotropic continuous positive definite kernel. The upper and lower bounds we present carry precise information about the asymptotic constants, depending on the dimension of the sphere and the monotonic behavior of the Schoenberg/Fourier coefficients of the isotropic kernel.

math.FA↗

arXiv2023

Sharp estimates for the covering numbers of the Weierstrass fractal kernel

In this paper, we present sharp estimates for the covering numbers of the embedding of the reproducing kernel Hilbert space (RKHS) associated with the Weierstrass fractal kernel into the space of continuous functions. The method we apply is based on the characterization of the infinite-dimensional RKHS generated by the Weierstrass fractal kernel and it requires estimates for the norm operator of orthogonal projections on the RKHS.

math.FA↗

arXiv2019

Super-exponential decay rates for eigenvalues and singular values of integral operators on the sphere

This paper brings results about the behavior of sequences of eigenvalues or singular values of integral operators generated by square-integrable kernels on the real m-dimensional unit sphere, $m\leq2$. Under smoothness assumptions on the generating kernels, given via Laplace-Beltrami differentiability, we obtain super-exponential decay rates for the eigenvalues of the generated positive integral operators and for singular values of those integral operators which are non-positive. We show an optimal-type result and provide a list of parametric families of kernels which are of interest for numerical analysis and geostatistical communities and satisfy the smoothness assumptions for the positive case.

math.FA↗

arXiv2018

On approximation tools and its applications on compact homogeneous spaces

We prove a characterization for the Peetre type $K$-functional on $\mathbb{M}$, a compact two-point homogeneous space, in terms the rate of approximation of a family of multipliers operator defined to this purpose. This extends the well known results on the spherical setting. The characterization is employed to show that an abstract Hölder condition or finite order of differentiability condition imposed on kernels generating certain operators implies a sharp decay rates for their eigenvalues sequences. The latest is employed to obtain estimates for the Kolmogorov $n$-width of unit balls in Reproducing Kernel Hilbert Space (RKHS).

math.FA↗