scholarly journals A class of gap series with small growth in the unit disc

Author(s):  
L. R. Sons ◽  
Zhuan Ye

Letβ>0and letαbe an integer which is at least2. Iffis an analytic function in the unit discDwhich has power series representationf(z)=∑k=0∞ak zkα,limsupk→∞ (log+|ak|/logk)=α(1+β), then the first author has proved thatfis unbounded in every sector{z∈D:Φ−ϵ<argz<Φ+ϵ, forϵ>0}. A natural conjecture concerning these functions is thatlimsupr→1−(logL(r)/logM(r))>0, whereL(r)is the minimum of|f(z)|on|z|=randM(r)is the maximum of|f(z)|on|z|=r. In this paper, investigations concerning this conjecture are discussed. For example, we prove thatlimsupr→1−(logL(r)/logM(r))=1andlimsupr→1−(L(r)/M(r))=0whenak=kα(1+β).

1983 ◽  
Vol 28 (3) ◽  
pp. 433-439
Author(s):  
K.S. Padmanabhan ◽  
M.S. Ganesan

The authors determine the sharp radius of convexity for functions analytic in the unit disc having power series representation of the form f(z) = z + an+1zn+1 + an+2zn+2 + … where an+1 is fixed and such that zf′(z)/f(x) = (1 + Aw(z))/(1 + Bw(z)), −1 ≤ B < 0 < A ≤ 1 where w(z) is an analytic function satisfying the conditions of Schwarz's lemma, in the case A + B ≥ 0. The estimate obtained is an improvement over the corresponding result obtained by Mogra and Juneja for functions analytic and starlike in the unit disc, with missing coefficients where the initial non-vanishing coefficient is fixed.


1981 ◽  
Vol 24 (3) ◽  
pp. 381-388 ◽  
Author(s):  
M.L. Mogra ◽  
O.P. Juneja

The authors determine the sharp radius of convexity for functions analytic and starlike in the unit disc having power series representation of the form where an+1 is fixed. The estimate obtained is an improvement over the corresponding fixed second coefficient result. It is expected that this approach will lead to sharpening and improvement of a number of earlier known results.


1984 ◽  
Vol 7 (3) ◽  
pp. 443-454
Author(s):  
M. L. Mogra ◽  
O. P. Juneja

We consider functionsfanalytic in the unit disc and assume the power series representation of the formf(z)=z+an+1zn+1+an+2zn+2+…wherean+1is fixed throughout. We provide a unified approach to radius convexity problems for different subclasses of univalent analytic functions. Numerous earlier estimates concerning the radius of convexity such as those involving fixed second coefficient,ninitial gaps,n+1symmetric gaps, etc. are discussed. It is shown that several known results, follow as special cases of those presented in this paper.


1983 ◽  
Vol 26 (4) ◽  
pp. 454-463
Author(s):  
Bruce L. R. Shawyer ◽  
Ludwig Tomm

AbstractThe behaviour of summability transforms of power series outside their circles of convergence has been studied by many authors. In the case of the geometric series Luh [6] and Tomm [10] showed that there exist regular methods A which provide an analytic continuation into any given simply connected region G that contains the unit disc but not the point 1. Moreover, the Atransforms of the geometric series may be required to converge to any chosen analytic function on prescribed regions outside the unit circle. In this paper, these results are extended to power series representing other meromorphic functions. It is also shown that the summability methods involved may be chosen to be generalized weighted means previously introduced by Faulstich [1].


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