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- Table of Contents
International Journal of Mathematics and Mathematical Sciences
Volume 2012 (2012), Article ID 309465, 9 pages
Coefficient Bounds for Certain Subclasses of Analytic Functions Defined by Komatu Integral Operator
School of Civil Aviation College, Kocaeli University, Arslanbey Campus, 41285 Izmit-Kocaeli, Turkey
Received 23 March 2012; Accepted 11 July 2012
Academic Editor: Yuri Latushkin
Copyright © 2012 Serap Bulut. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
We determine the coeffcient bounds for functions in certain subclasses of analytic functions of complex order, which are introduced here by means of a certain non-homogeneous Cauchy–Euler type differential equation of order m. Relevant connections of some of the results obtained with those in earlier works are also provided.
1. Introduction, Definitions and Preliminaries
Let be the set of real numbers, let be the set of complex numbers, be the set of positive integers and
Let denote the class of functions of the form which are analytic in the unit disk:
Recently, Komatu  introduced a certain integral operator defined by
Using the relation (1.6), it is easily verfied that
We note that:(i)for and ( is any integer), the multiplier transformation was studied by Flett  and Sălageăn ;(ii)for and (), the differential operator was studied by Sălageăn ;(iii)for and ( is any integer), the operator was studied by Uralegaddi and Somanatha ;(iv)for , the multiplier transformation was studied by Jung et al. .
Using the operator , we now introduce the following classes.
Definition 1.1. One says that a function is in the class if where .
Definition 1.2. One says that a function is in the class if
Note that In particular, the classes introduced by Bulut .
Making use of the Komatu integral operator , we now introduce each of the following subclasses of analytic functions.
Definition 1.3. One denotes by the class of functions satisfying where .
Definition 1.4. A function is said to be in the class if it satisfies the following non-homogenous Cauchy-Euler differential equation:
Remark 1.5. If we set in the classes and , then we have the classes
introduced by Srivastava et al. , respectively.
If we take and in the class , then we have a new class consisting of functions which satisfy the condition We denote this class by . Also we denote by for corresponding class to .
Note that taking and for the class , we have the classes and , respectively. In particular, the classes are studied by Altıntaş et al. .
In this work, by using the principle of subordination, we obtain coefficient bounds for functions in the subclasses of analytic functions of complex order, which we have introduced here. Our results would unify and extend the corresponding results obtained earlier by Robertson , Nasr and Aouf , Altıntaş et al.  and Srivastava et al. .
In our investigation, we will make use of the principle of subordination between analytic functions, which is explained in Definition 1.6 below (see ).
Definition 1.6. For two functions and , analytic in , one says that the function is subordinate to in , and write
if there exists a Schwarz function , analytic in , with
In particular, if the function is univalent in , the above subordination is equivalent to
In order to prove our main results (Theorems 2.1 and 2.2 in Section 2), we first recall the following lemma due to Rogosinski .
Lemma 1.7. Let the function given by be convex in . Also let the function given by be holomorphic in . If then
2. The Main Results and Their Demonstration
Theorem 2.1. Let the function be defined by (1.3). If the function is in the class , then
Proof. Let the function be given by (1.3). Define a function We note that the function is of the form where, for convenience, From Definition 1.3 and (2.2), we obtain that Let us set and define the function by Therefore, we have Hence, by Definition 1.6, we deduce that Note that Also from (2.7), we find Let Since , in view of (2.3), (2.11) and (2.12), we obtain for . On the other hand, according to the Lemma 1.7, we obtain By combining (2.14) and (2.13), for , we obtain respectively. Using the principle of mathematical induction, we obtain Now from (2.4), it is clear that This evidently completes the proof of Theorem 2.1.
Theorem 2.2. Let the function be defined by (1.3). If the function is in the class , then
3. Corollaries and Consequences
Corollary 3.1. Let the function be defined by (1.3). If the function is in the class , then
Corollary 3.3. Let the function be defined by (1.3). If the function is in the class , then
Letting and in Corollary 3.1, we get following corollaries, respectively.
Corollary 3.5. Let the function be defined by (1.3). If the function is in the class , then
Corollary 3.6. Let the function be defined by (1.3). If the function is in the class , then
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