Le théorème classique de Riesz-Raikov assure que, pour tout entier $\theta \>1$ et toute $f$ de $L^1\left(𝕋\right)$, où $𝕋=ℝ/\mathbb{Z}$, les moyennes$$\frac{1}{N}\sum _1^{N}f\left({\theta }^{n}x\right)\text{convergent}\text{vers}{\int }_{𝕋}f\left(t\right)\mathrm{d}t$$pour presque tout point $x$ de $ℝ$. J.Bourgain (cf.Israël Math. Conf. Proc. 1990) a prouvé que la convergence précédente a lieu pour tout réel algébrique $\theta \>1$ et toute $f$ de $L^2\left(𝕋\right)$. Dans cet article nous prouvons que, si $\varphi$ est un endomorphisme de ${ℝ}^p$ algébrique sur $\mathbb{Q}$, dont les valeurs propres sont toutes de module $\>1$, alors pour toute $f$ de $L^2\left({𝕋}^p\right)$, les moyennes $(1/N){\sum }_1^{N}f\left({\varphi }^{n}x\right)$ convergent vers ${\int }_{{𝕋}^p}f\left(t\right)\mathrm{d}t$ pour presque tout point $x$ de ${ℝ}^p$. Nous...

Nous étudons sur des exemples significatifs l’intersection entre le traitement du signal et l’analyse fonctionnelle.

We present an estimation of the $H_{k₀,k_r}^{q,\alpha }f$ and $H_{\lambda ,u}^{\varphi ,\alpha }f$ means as approximation versions of the Totik type generalization (see [5], [6]) of the result of G. H. Hardy, J. E. Littlewood. Some corollaries on the norm approximation are also given.

A general notion of lifting properties for families of sesquilinear forms is formulated. These lifting properties, which appear as particular cases in many classical interpolation problems, are studied for the Toeplitz kernels in Z, and applied for refining and extending the Nehari theorem and the Paley lacunary inequality.

Let T be a self-adjoint tridiagonal operator in a Hilbert space H with the orthonormal basis {e n}n=1∞, σ(T) be the spectrum of T and Λ(T) be the set of all the limit points of eigenvalues of the truncated operator T N. We give sufficient conditions such that the spectrum of T is discrete and σ(T) = Λ(T) and we connect this problem with an old problem in analysis.

The estimate ${∥D^{k-1}u∥}_{L^{n/(n-1)}}\le {∥A\left(D\right)u∥}_{L^1}$ is shown to hold if and only if $A\left(D\right)$ is elliptic and canceling. Here $A\left(D\right)$ is a homogeneous linear differential operator $A\left(D\right)$ of order $k$ on ${ℝ}^n$ from a vector space $V$ to a vector space $E$. The operator $A\left(D\right)$ is defined to be canceling if ${\bigcap }_{\xi \in {ℝ}^n\setminus \left\{0\right\}}A\left(\xi \right)\left[V\right]=\left\{0\right\}$. This result implies in particular the classical Gagliardo–Nirenberg–Sobolev inequality, the Korn–Sobolev inequality and Hodge–Sobolev estimates for differential forms due to J. Bourgain and H. Brezis. In the proof, the class of cocanceling homogeneous linear differential...

Multiplicatively invariant (MI) spaces are closed subspaces of L²(Ω, ) that are invariant under multiplication by (some) functions in $L^{\infty }\left(\Omega \right)$; they were first introduced by Bownik and Ross (2014). In this paper we work with MI spaces that are finitely generated. We prove that almost every set of functions constructed by taking linear combinations of the generators of a finitely generated MI space is a new set of generators for the same space, and we give necessary and sufficient conditions on the linear...

The main object of this paper is to investigate several general families of hypergeometric polynomials and their associated multiple integral representations. By suitably specializing our main results, the corresponding integral representations are deduced for such familiar classes of hypergeometric polynomials as (for example) the generalized Bedient polynomials of the first and second kinds. Each of the integral representations, which are derived in this paper, may be viewed also as a linearization...

The extremal functions f0(z) realizing the maxima of some functionals (e.g. max |a3|, and max arg f′(z)) within the so-called universal linearly invariant family Uα (in the sense of Pommerenke [10]) have such a form that f′0(z) looks similar to generating function for Meixner-Pollaczek (MP) polynomials [2], [8]. This fact gives motivation for the definition and study of the generalized Meixner-Pollaczek (GMP) polynomials Pλn (x; θ,ψ) of a real variable x as coefficients of [###] where the parameters...