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

Abstract

This study deals with analytic functions with bounded turnings, defined in the disk Od=z:z1. These functions are subordinated by sigmoid function 21+e−z and their class is denoted by BTSg. Sharp coefficient inequalities, including the third Hankel determinant for class BTSg, were investigated here. The same was also included for the logarithmic coefficients related to functions of the class BTSg.

Keywords

• bounded turning function
• logarithmic coefficients
• Hankel determinant
• sigmoid function