arXiv subjects

Egor A. Maximenko

Publications and source records attributed to Egor A. Maximenko.

At least 19 recordsLinked to original sources

arXiv2026

Eigenvalues of the tetradiagonal Toeplitz matrices with diagonals 1, 0, 0, 1

We perform a thorough analysis of the eigenvalues of tetradiagonal Toeplitz matrices of large order $n$ generated by the Laurent polynomial $a(t)=t^2+t^{-1}$. The spectra of these matrices are invariant under $2\pi/3$-rotation. They are contained in three segments of the complex plane and asymptotically fill these segments as $n$ tends to infinity. We apply Widom's formula for the determinants and transform the characteristic equation into a convenient form that can be solved by the fixed point iteration method. After that, we compute the asymptotic distribution of the eigenvalues. The main results are asymptotic formulas for the eigenvalues, both close to the origin and far from the origin. The main results are verified by numerical tests for moderate values of $n$.

math.SP↗

arXiv2026

Locally similar distances and equality of the induced intrinsic distances

Let $X$ be a set and $d_1,d_2$ be two distances on $X$. We say that $d_1$ and $d_2$ are locally similar and write $d_1\cong d_2$ if $d_1$ and $d_2$ are topologically equivalent and, for every $a$ in $X$, \[ \lim_{x\to a} \frac{d_2(x,a)}{d_1(x,a)}=1. \] We prove that if $d_1\cong d_2$, then the intrinsic distances induced by $d_1$ and $d_2$ coincide. We also provide sufficient conditions for $d_1\cong d_2$ and consider several examples related to reproducing kernel Hilbert spaces.

math.MG↗

arXiv2025

Integral representation of translation-invariant operators on reproducing kernel Hilbert spaces

We suppose that $G$ is a locally compact abelian group, $Y$ is a measure space, and $H$ is a reproducing kernel Hilbert space on $G\times Y$ such that $H$ is naturally embedded into $L^2(G\times Y)$ and it is invariant under the translations associated with $G$. We consider the von Neumann algebra of all bounded linear operators acting on $H$ that commute with these translations. Assuming that this algebra is commutative, we represent its elements as integral operators and characterize the corresponding integral kernels. Furthermore, we give W*-algebra structure on the functions associated with the integral kernels. We apply this general scheme to a series of examples, including rotation- or translation-invariant operators in Bergman or Fock spaces.

math.OA↗

arXiv2025

Toeplitz operators in Bergman space induced by radial measures

We study radial Carleson--Bergman measures on the unit disk and the corresponding Toeplitz operators acting in the Bergman space. First, we show that such Toeplitz operators are diagonal in the canonical basis, and we compute their eigenvalue sequences and Berezin transforms in terms of the radial component of the measure. Next, considering the average values of radial measures near the boundary, we give a simple characterization of radial Carleson--Bergman measures. Finally, we prove that the eigenvalue sequences of such Toeplitz operators are Lipschitz continuous with respect to the logarithmic distance on natural numbers. As a consequence, we describe the commutative C*-algebra generated by Toeplitz operators induced by radial Carleson--Bergman measures.

math.FA↗

arXiv2025

Constructive approximation of convergent sequences by eigenvalue sequences of radial Toeplitz--Fock operators

It is well known that for every measurable function $a$, essentially bounded on the positive halfline, the corresponding radial Toeplitz operator $T_a$, acting in the Segal--Bargmann--Fock space, is diagonal with respect to the canonical orthonormal basis consisting of normalized monomials. We denote by $γ_a$ the corresponding eigenvalues sequence. Given an arbitrary convergent sequence, we uniformly approximate it by sequences of the form $γ_a$ with any desired precision. We give a simple recipe for constructing $a$ in terms of Laguerre polynomials. Previously, we proved this approximation result with nonconstructive tools (Esmeral and Maximenko, ``Radial Toeplitz operators on the Fock space and square-root-slowly oscillating sequences'', Complex Anal. Oper. Theory 10, 2016). In the present paper, we also include some properties of the sequences $γ_a$ and some properties of bounded sequences, uniformly continuous with respect to the sqrt-distance on natural numbers.

math.FA↗

arXiv2024

Complete homogeneous symmetric polynomials with repeating variables

We consider polynomials of the form $\operatorname{h}_m(y_1^{[\varkappa_1]},\ldots,y_n^{[\varkappa_n]})$, where $\operatorname{h}_m$ is the complete homogeneous polynomial of degree $m$ and $y_j^{[\varkappa_j]}$ denotes $y_j$ repeated $\varkappa_j$ times. Using the decomposition of the generating function into partial fractions we represent such polynomials in the form \[ \operatorname{h}_m(y_1^{[\varkappa_1]},\ldots,y_n^{[\varkappa_n]}) =\sum_{j=1}^n \sum_{r=1}^{\varkappa_j} \binom{r+m-1}{r-1} A_{y,\varkappa,j,r} y_j^m, \] where $A_{y,\varkappa,j,r}$ are some coefficients that do not depend on $m$. We also provide an alternative proof using the inverse of the confluent Vandermonde matrix.

math.CO↗

arXiv2023

Bialternant formula for Schur polynomials with repeating variables

We consider polynomials of the form $\operatorname{s}_λ(y_1^{[\varkappa_1]},\ldots,y_n^{[\varkappa_n]})$, where $λ$ is an integer partition, $\operatorname{s}_λ$ is the Schur polynomial associated to $λ$, and $y_j^{[\varkappa_j]}$ denotes $y_j$ repeated $\varkappa_j$ times. We represent $\operatorname{s}_λ(y_1^{[\varkappa_1]},\ldots,y_n^{[\varkappa_n]})$ as a quotient whose the denominator is the determinant of the confluent Vandermonde matrix, and the numerator is the determinant of some generalized confluent Vandermonde matrix. We give three algebraic proofs of this formula.

math.CO↗

arXiv2023

Horizontal Fourier transform of the polyanalytic Fock kernel

Let $n,m\ge 1$ and $α>0$. We denote by $\mathcal{F}_{α,m}$ the $m$-analytic Bargmann--Segal--Fock space, i.e., the Hilbert space of all $m$-analytic functions defined on $\mathbb{C}^n$ and square integrables with respect to the Gaussian weight $\exp(-α|z|^2)$. We study the von Neumann algebra $\mathcal{A}$ of bounded linear operators acting in $\mathcal{F}_{α,m}$ and commuting with all ``horizontal'' Weyl translations, i.e., Weyl unitary operators associated to the elements of $\mathbb{R}^n$. The reproducing kernel of $\mathcal{F}_{1,m}$ was computed by Youssfi [Polyanalytic reproducing kernels in $\mathbb{C}^n$, Complex Anal. Synerg., 2021, 7, 28]. Multiplying the elements of $\mathcal{F}_{α,m}$ by an appropriate weight, we transform this space into another reproducing kernel Hilbert space whose kernel $K$ is invariant under horizontal translations. Using the well-known Fourier connection between Laguerre and Hermite functions, we compute the Fourier transform of $K$ in the ``horizontal direction'' and decompose it into the sum of $d$ products of Hermite functions, with $d=\binom{n+m-1}{n}$. Finally, applying the scheme proposed by Herrera-Yañez, Maximenko, Ramos-Vazquez [Translation-invariant operators in reproducing kernel Hilbert spaces, Integr. Equ. Oper. Theory, 2022, 94, 31], we show that $\mathcal{F}_{α,m}$ is isometrically isomorphic to the space of vector-functions $L^2(\mathbb{R}^n)^d$, and $\mathcal{A}$ is isometrically isomorphic to the algebra of matrix-functions $L^\infty(\mathbb{R}^n)^{d\times d}$.

math.FA↗

arXiv2023

C*-algebras generated by radial Toeplitz operators on polyanalytic weighted Bergman spaces

In a previous paper (Radial operators on polyanalytic weighted Bergman spaces, Bol. Soc. Mat. Mex. 27, 43), using disk polynomials as an orthonormal basis in the $n$-analytic weighted Bergman space, we showed that for every bounded radial generating symbol $a$, the associated Toeplitz operator, acting in this space, can be identified with a matrix sequence $γ(a)$, where the entries of the matrices are certain integrals involving $a$ and Jacobi polynomials. In this paper, we suppose that the generating symbols $a$ have finite limits on the boundary and prove that the C*-algebra generated by the corresponding matrix sequences $γ(a)$ is the C*-algebra of all matrix sequences having scalar limits at infinity. We use Kaplansky's noncommutative analog of the Stone--Weierstrass theorem and some ideas from several papers by Loaiza, Lozano, Ramírez-Ortega, Ramírez-Mora, and Sánchez-Nungaray. We also prove that for $n\ge 2$, the closure of the set of matrix sequences $γ(a)$ is not equal to the generated C*-algebra.

math.OA↗

arXiv2022

Eigenvalues of the laplacian matrices of the cycles with one weighted edge

In this paper we study the eigenvalues of the laplacian matrices of the cyclic graphs with one edge of weight $α$ and the others of weight $1$. We denote by $n$ the order of the graph and suppose that $n$ tends to infinity. We notice that the characteristic polynomial and the eigenvalues depend only on $\operatorname{Re}(α)$. After that, through the rest of the paper we suppose that $0<α<1$. It is easy to see that the eigenvalues belong to $[0,4]$ and are asymptotically distributed as the function $g(x)=4\sin^2(x/2)$ on $[0,π]$. We obtain a series of results about the individual behavior of the eigenvalues. First, we describe more precisely their localization in subintervals of $[0,4]$. Second, we transform the characteristic equation to a form convenient to solve by numerical methods. In particular, we prove that Newton's method converges for every $n\ge3$. Third, we derive asymptotic formulas for all eigenvalues, where the errors are uniformly bounded with respect to the number of the eigenvalue.

math.FA↗

arXiv2021

Translation-invariant operators in reproducing kernel Hilbert spaces

Let $G$ be a locally compact abelian group with a Haar measure, and $Y$ be a measure space. Suppose that $H$ is a reproducing kernel Hilbert space of functions on $G\times Y$, such that $H$ is naturally embedded into $L^2(G\times Y)$ and is invariant under the translations associated with the elements of $G$. Under some additional technical assumptions, we study the W*-algebra $\mathcal{V}$ of translation-invariant bounded linear operators acting on $H$. First, we decompose $\mathcal{V}$ into the direct integral of the W*-algebras of bounded operators acting on the reproducing kernel Hilbert spaces $\widehat{H}_ξ$, $ξ\in\widehat{G}$, generated by the Fourier transform of the reproducing kernel. Second, we give a constructive criterion for the commutativity of $\mathcal{V}$. Third, in the commutative case, we construct a unitary operator that simultaneously diagonalizes all operators belonging to $\mathcal{V}$, i.e., converts them into some multiplication operators. Our scheme generalizes many examples previously studied by Nikolai Vasilevski and other authors.

math.FA↗

arXiv2021

Approximately invertible elements in non-unital normed algebras

We introduce a concept of approximately invertible elements in non-unital normed algebras which is, on one side, a natural generalization of invertibility when having approximate identities at hand, and, on the other side, it is a direct extension of topological invertibility to non-unital algebras. Basic observations relate approximate invertibility with concepts of topological divisors of zero and density of (modular) ideals. We exemplify approximate invertibility in the group algebra, Wiener algebras, and operator ideals. For Wiener algebras with approximate identities (in particular, for the Fourier image of the convolution algebra), the approximate invertibility of an algebra element is equivalent to the property that it does not vanish. We also study approximate invertibility and its deeper connection with the Gelfand and representation theory in non-unital abelian Banach algebras as well as abelian and non-abelian C*-algebras.

math.FA↗

arXiv2021

Homogeneously polyanalytic kernels on the unit ball and the Siegel domain

We prove that the homogeneously polyanalytic functions of total order $m$, defined by the system of equations $\overline{D}^{(k_1,\ldots,k_n)} f=0$ with $k_1+\cdots+k_n=m$, can be written as polynomials of total degree $<m$ in variables $\overline{z_1},\ldots,\overline{z_n}$, with some analytic coefficients. We establish a weighted mean value property for such functions, using a reproducing property of Jacobi polynomials. After that, we give a general recipe to transform a reproducing kernel by a weighted change of variables. Applying these tools, we compute the reproducing kernel of the Bergman space of homogeneously polyanalytic functions on the unit ball in $\mathbb{C}^n$ and on the Siegel domain. For the one-dimensional case, analogous results were obtained by Koshelev (1977), Pessoa (2014), Hachadi and Youssfi (2019).

math.CV↗

arXiv2020

Radial operators on polyanalytic weighted Bergman spaces

Let $μ_α$ be the Lebesgue plane measure on the unit disk with the radial weight $\frac{α+1}π(1-|z|^2)^α$. Denote by $\mathcal{A}^{2}_{n}$ the space of the $n$-analytic functions on the unit disk, square-integrable with respect to $μ_α$. Extending the results of Ramazanov (1999, 2002), we explain that disk polynomials (studied by Koornwinder in 1975 and Wünsche in 2005) form an orthonormal basis of $\mathcal{A}^{2}_{n}$. Using this basis, we provide the Fourier decomposition of $\mathcal{A}^{2}_{n}$ into the orthogonal sum of the subspaces associated with different frequencies. This leads to the decomposition of the von Neumann algebra of radial operators, acting in $\mathcal{A}^{2}_n$, into the direct sum of some matrix algebras. In other words, all radial operators are represented as matrix sequences. In particular, we represent in this form the Toeplitz operators with bounded radial symbols, acting in $\mathcal{A}^{2}_n$. Moreover, using ideas by Engliš (1996), we show that the set of all Toeplitz operators with bounded generating symbols is not weakly dense in $\mathcal{B}(\mathcal{A}^{2}_n)$.

math.FA↗

arXiv2020

Eigenvalues of tridiagonal Hermitian Toeplitz matrices with perturbations in the off-diagonal corners

In this paper we study the eigenvalues of Hermitian Toeplitz matrices with the entries $2,-1,0,\ldots,0,-α$ in the first column. Notice that the generating symbol depends on the order $n$ of the matrix. If $|α|\le 1$, then the eigenvalues belong to $[0,4]$ and are asymptotically distributed as the function $g(x)=4\sin^2(x/2)$ on $[0,π]$. The situation changes drastically when $|α|>1$ and $n$ tends to infinity. Then the two extreme eigenvalues (the minimal and the maximal one) lay out of $[0,4]$ and converge rapidly to certain limits determined by the value of $α$, whilst all others belong to $[0,4]$ and are asymptotically distributed as $g$. In all cases, we transform the characteristic equation to a form convenient to solve by numerical methods, and derive asymptotic formulas for the eigenvalues.

math.FA↗

arXiv2019

Symmetric polynomials in the symplectic alphabet and their expression via Dickson--Zhukovsky variables

Given a symmetric polynomial $P$ in $2n$ variables, there exists a unique symmetric polynomial $Q$ in $n$ variables such that \[ P(x_1,\ldots,x_n,x_1^{-1},\ldots,x_n^{-1}) =Q(x_1+x_1^{-1},\ldots,x_n+x_n^{-1}). \] We denote this polynomial $Q$ by $Φ_n(P)$ and show that $Φ_n$ is an epimorphism of algebras. We compute $Φ_n(P)$ for several families of symmetric polynomials $P$: symplectic and orthogonal Schur polynomials, elementary symmetric polynomials, complete homogeneous polynomials, and power sums. Some of these formulas were already found by Elouafi (2014) and Lachaud (2016). The polynomials of the form $Φ_n(\operatorname{s}_{λ/μ}^{(2n)})$, where $\operatorname{s}_{λ/μ}^{(2n)}$ is a skew Schur polynomial in $2n$ variables, arise naturally in the study of the minors of symmetric banded Toeplitz matrices, when the generating symbol is a palindromic Laurent polynomial, and its roots can be written as $x_1,\ldots,x_n,x^{-1}_1,\ldots,x^{-1}_n$. Trench (1987) and Elouafi (2014) found efficient formulas for the determinants of symmetric banded Toeplitz matrices. We show that these formulas are equivalent to the result of Ciucu and Krattenthaler (2009) about the factorization of the characters of classical groups.

math.CO↗

arXiv2019

Radial operators on polyanalytic Bargmann-Segal-Fock spaces

The paper considers bounded linear radial operators on the polyanalytic Fock spaces $\mathcal{F}_n$ and on the true-polyanalytic Fock spaces $\mathcal{F}_{(n)}$. The orthonormal basis of normalized complex Hermite polynomials plays a crucial role in this study; it can be obtained by the orthogonalization of monomials in $z$ and $\overline{z}$. First, using this basis, we decompose the von Neumann algebra of radial operators, acting in $\mathcal{F}_n$, into the direct sum of some matrix algebras, i.e. radial operators are represented as matrix sequences. Secondly, we prove that the radial operators, acting in $\mathcal{F}_{(n)}$, are diagonal with respect to the basis of the complex Hermite polynomials belonging to $\mathcal{F}_{(n)}$. We also provide direct proofs of the fundamental properties of $\mathcal{F}_n$ and an explicit description of the C*-algebra generated by Toeplitz operators in $\mathcal{F}_{(n)}$, whose generating symbols are radial, bounded, and have finite limits at infinity.

math.OA↗

arXiv2017

Eigenvalues of even very nice Toeplitz matrices can be unexpectedly erratic

It was shown in a series of recent publications that the eigenvalues of $n\times n$ Toeplitz matrices generated by so-called simple-loop symbols admit certain regular asymptotic expansions into negative powers of $n+1$. On the other hand, recently two of the authors considered the pentadiagonal Toeplitz matrices generated by the symbol $g(x)=(2\sin(x/2))^4$, which does not satisfy the simple-loop conditions, and derived asymptotic expansions of a more complicated form. We here use these results to show that the eigenvalues of the pentadiagonal Toeplitz matrices do not admit the expected regular asymptotic expansion. This also delivers a counter-example to a conjecture by Ekström, Garoni, and Serra-Capizzano and reveals that the simple-loop condition is essential for the existence of the regular asymptotic expansion.

math.FA↗