Mathematics
Geometric properties of the Bernatsky integral operator
F. F. Mayer,
M. G. Tastanov,
A. A. Utemisova Kostanay Regional University named after A. Baitursynov, Kostanay, Republic of Kazakhstan
Abstract:
In the geometric theory of complex variable functions, the study of mapping of classes of regular functions using various operators has now become an independent trend. The connection $f(z)\in S^{o}\Leftrightarrow g(z) = zf'(z) \in S^*$ of the classes
$S^{o}$ and
$S^*$ of convex and star-shaped functions can be considered as mapping using the differential operator
$G[f](x) = zf'(z)$ of class
$S^{o}$ to class
$S^*$, that is,
$G: S^{o} \to S^*$ or
$G(S^{o}) = S^*$. The impetus for studying this range of issues was M. Bernatsky's assumption that the inverse operator
$G^{-1}[f](x)$, which translates
$S^* \to S^{o}$ and thereby “improves” the properties of functions, maps the entire class
$S$ of single-leaf functions into itself.
At present, a number of articles have been published which study the various integral operators. In particular, they establish sets of values of indicators included in these operators where operators map class
$S$ or its subclasses to themselves or to other subclasses.
This paper determines the values of the Bernatsky parameter included in the generalized integral operator, at which this operator transforms a subclass of star-shaped functions allocated by the condition
$a < \mathrm{Re}\, zf'(z)/f(z) < b$ (
$0 < a < 1 < b$), in the class
$K(\gamma)$ of functions, almost convex in order
$\gamma$. The results of the article summarize or reinforce previously known effects.
Keywords:
geometric theory of functions of a complex variable, single-leaf functions, Bernatsky integral operator, convex, star-shaped and almost convex functions.
UDC:
517.54 Received: 18.01.2022
DOI:
10.14529/mmph220402