Tangent approximation by solutions of the convolution equation
Problemy analiza, Tome 11 (2022) no. 3, pp. 125-142

Voir la notice de l'article provenant de la source Math-Net.Ru

The article for the first time studies the approximation of a function together with its derivatives on the real line by solutions of a multidimensional convolution equation of the form $$g\ast T=0,$$ where $T$ is a given compactly supported radial distribution other than a constant multiplied by the Dirac delta function at zero. The following analogue of the well-known Carleman's theorem on tangent approximation by entire functions is obtained: if $f\in C^k(\mathbb{R})$ for some $k\in\mathbb{Z}_+$ and for any $\nu\in\{0, \ldots, k\}$ there is a finite limit \begin{equation*} \displaystyle \underset{t \to +0 }\lim \left(\frac{d}{dt}\right)^{\nu}f(\mathrm{ln}t), \end{equation*} then for an arbitrary positive continuous function $\varepsilon(t)$ on $\mathbb{R}$ there exists an entire function $\Phi\colon\mathbb{C}^n\to \mathbb{C}$, such that $\Phi\big |_{\mathbb{R}^n}\ast T=0$ and \begin{equation*} \left|f^{(\nu)}(t)-\left(\frac{\partial}{\partial x_1}\right)^{\nu}\Phi(t, 0, \ldots, 0)\right|\varepsilon(e^t) \end{equation*} for all $t\in\mathbb{R}$, $\nu\in\{0, \ldots, k\}$ (Theorem 1). It is shown that when approximating a function on subsets of the real line that do not contain a neighborhood of the point $-\infty$, the condition for the existence of a limit in Theorem 1 can be omitted. In addition, the method of proving Theorem 1 allows one to obtain new results that are of interest for the theory of convolution equations of the indicated type. These are results about the growth of solutions (Corollary 3), on the distribution of values (Theorem 2), and also on the solvability of the interpolation problem for solutions of the convolution equation (Corollary 4).
Keywords: mean periodicity, Carleman's approximation theorem.
Mots-clés : convolution equation
@article{PA_2022_11_3_a8,
     author = {V. V. Volchkov and Vit. V. Volchkov},
     title = {Tangent approximation by solutions of the convolution equation},
     journal = {Problemy analiza},
     pages = {125--142},
     publisher = {mathdoc},
     volume = {11},
     number = {3},
     year = {2022},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PA_2022_11_3_a8/}
}
TY  - JOUR
AU  - V. V. Volchkov
AU  - Vit. V. Volchkov
TI  - Tangent approximation by solutions of the convolution equation
JO  - Problemy analiza
PY  - 2022
SP  - 125
EP  - 142
VL  - 11
IS  - 3
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/PA_2022_11_3_a8/
LA  - en
ID  - PA_2022_11_3_a8
ER  - 
%0 Journal Article
%A V. V. Volchkov
%A Vit. V. Volchkov
%T Tangent approximation by solutions of the convolution equation
%J Problemy analiza
%D 2022
%P 125-142
%V 11
%N 3
%I mathdoc
%U http://geodesic.mathdoc.fr/item/PA_2022_11_3_a8/
%G en
%F PA_2022_11_3_a8
V. V. Volchkov; Vit. V. Volchkov. Tangent approximation by solutions of the convolution equation. Problemy analiza, Tome 11 (2022) no. 3, pp. 125-142. http://geodesic.mathdoc.fr/item/PA_2022_11_3_a8/