Subclasses of typically real functions determined by some modular inequalities

Leopold Koczan, Katarzyna Trąbka-Więcław

Abstract


Let \(\mathrm{T}\) be the family of all typically real functions, i.e. functions that are analytic in the unit disk \(\Delta := \{ z \in \mathbb{C} : |z|<1 \}\), normalized by \(f(0)=f'(0)-1=0\) and such that Im \(z\) Im \(f(z)\) \(\geq 0\) for \(z \in \Delta\). Moreover, let us denote: \(\mathrm{T}^{(2)}:=  \{f \in \mathrm{T}: f(z)=-f(-z) \text{ for } z \in \Delta \}\) and \(\mathrm{T}^{M,g} :=  \{ f \in \mathrm{T}: f \prec Mg \text{ in } \Delta \}\), where \(M>1\), \(g \in \mathrm{T} \cap \mathrm{S}\) and \(\mathrm{S}\) consists of all analytic functions, normalized and univalent in \(\Delta\).
We investigate  classes in which the subordination is replaced with the majorization and the function \(g\) is typically real but does not necessarily univalent, i.e. classes \(\{ f \in \mathrm{T}: f \ll Mg \text{ in } \Delta \}\), where \(M>1\), \(g \in \mathrm{T}\), which we denote by \(\mathrm{T}_{M,g}\). Furthermore, we broaden the class \(\mathrm{T}_{M,g}\) for the case \(M \in (0,1)\) in the following  way:
\(\mathrm{T}_{M,g} = \left\{ f \in \mathrm{T} : |f(z)| \geq M |g(z)| \text{ for } z \in \Delta \right\}\), \(g \in \mathrm{T}\).

Keywords


Typically real functions; majorization; subordination

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References


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DOI: http://dx.doi.org/10.17951/a.2010.54.1.75-80
Data publikacji: 2016-07-29 22:06:17
Data złożenia artykułu: 2016-07-29 21:32:18

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Copyright (c) 2010 Leopold Koczan, Katarzyna Trąbka-Więcław