The Bohr radius and the Hadamard convolution operator

Abstract

The concept of the Bohr radius of a pair of operators is introduced. In terms of the convolution function, a general formula for calculating the Bohr radius of the Hadamard convolution type operator with a fixed initial coefficient is obtained. We apply this formula to the problems of the Bohr radius of the operators of differentiation and integration. Using the concept of the Bohr radius of a pair of operators, we generalize the theorem of B. Bhowmik and N. Das on the comparison of majorant series of subordinate functions.