On bounded univalent functions whose ranges contain a fixed disk

Author:

Barnard Roger W.

Abstract

Let S \mathcal {S} denote the standard normalized class of regular, univalent functions in K = K 1 = { z : | z | > 1 } K = {K_1} = \{ z:|z| > 1\} . Let F \mathcal {F} be a given compact subclass of S \mathcal {S} . We consider the following two problems. Problem 1. Find max | a 2 | \max |{a_2}| for f F f \in \mathcal {F} . Problem 2. For | z | = r > 1 |z| = r > 1 , find the max ( min ) | f ( z ) | \max \;(\min )|f(z)| for f F f \in \mathcal {F} . In this paper we are concerned with the subclass S d ( M ) = { f S : K d f ( K ) K M } \mathcal {S}_d^\ast (M) = \{ f \in \mathcal {S}:{K_d} \subset f(K) \subset {K_M}\} . Through the use of the Julia variational formula and the Loewner theory we determine the extremal functions for Problems 1 and 2 for the class S d ( M ) \mathcal {S}_d^\ast (M) , for all d, M such that 1 4 d 1 M \tfrac {1}{4} \leqslant d \leqslant 1 \leqslant M \leqslant \infty .

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

Reference14 articles.

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2. Translations of Mathematical Monographs, Vol. 26;Goluzin, G. M.,1969

3. Cambridge Tracts in Mathematics and Mathematical Physics, No. 48;Hayman, W. K.,1958

4. A variational method for starlike functions;Hummel, J. A.;Proc. Amer. Math. Soc.,1958

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