Coefficient estimates for $m$-fold symmetric bi-subordinate functions

Year 2019, Volume: 48 Issue: 2, 365 - 371, 01.04.2019

Ebrahim A. Adegani , Samaneh G. Hamidi , Jay M. Jahangiri , Ahmad Zireh

https://doi.org/10.15672/hujms.545237

https://izlik.org/JA26ZX37LU

Abstract

A function is said to be bi-univalent in the open unit disk $\mathbb{U}$ if both the function and its inverse map are univalent in $\mathbb{U}$. By the same token, a function is said to be bi-subordinate in $\mathbb{U}$ if both the function and its inverse map are subordinate to a given function in $\mathbb{U}$. In this paper, we consider the m-fold symmtric transform of such functions and use their Faber polynomial expansions to find upper bounds for their n-th ($n\geq 3$) coefficients subject to a given gap series condition. We also determine bounds for the first two coefficients of such functions with no restrictions imposed.

Keywords

Faber polynomials , $m$-fold symmetric , bi-univalent functions

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