Sharp Coefficient Problems of Functions with Bounded Turnings Subordinated by Sigmoid Function

Muhammad Arif, Safa Marwa, Qin Xin, Fairouz Tchier, Muhammad Ayaz and Sarfraz Nawaz Malik ()
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Muhammad Arif: Faculty of Physical and Numerical Sciences, Abdul Wali Khan University Mardan, Mardan 23200, Pakistan
Safa Marwa: Faculty of Physical and Numerical Sciences, Abdul Wali Khan University Mardan, Mardan 23200, Pakistan
Qin Xin: Faculty of Science and Technology, University of the Faroe Islands, Vestarabryggja 15, FO 100 Torshavn, Faroe Islands, Denmark
Fairouz Tchier: Department of Mathematics, College of Science, King Saud University, P.O. Box 22452, Riyadh 11495, Saudi Arabia
Muhammad Ayaz: Faculty of Physical and Numerical Sciences, Abdul Wali Khan University Mardan, Mardan 23200, Pakistan
Sarfraz Nawaz Malik: Department of Mathematics, COMSATS University Islamabad, Wah Campus, Wah Cantt 47040, Pakistan

Mathematics, 2022, vol. 10, issue 20, 1-24

Abstract: This study deals with analytic functions with bounded turnings, defined in the disk O d = z : z < 1 . These functions are subordinated by sigmoid function 2 1 + e − z and their class is denoted by BT Sg . Sharp coefficient inequalities, including the third Hankel determinant for class BT Sg , were investigated here. The same was also included for the logarithmic coefficients related to functions of the class BT Sg .

Keywords: bounded turning function; logarithmic coefficients; Hankel determinant; sigmoid function (search for similar items in EconPapers)
JEL-codes: C (search for similar items in EconPapers)
Date: 2022
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