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Journal of Complex Analysis
Volume 2013 (2013), Article ID 690584, 4 pages
Starlikeness of General Integral Operator for Meromorphic Multivalent Functions
1School of Liberal Studies, Bharat Ratna Dr B.R. Ambedkar University, Delhi 110006, India
2Civil Aviation College, Kocaeli University, Arslanbey Campus, 41285 Kocaeli, Turkey
Received 31 August 2012; Accepted 30 November 2012
Academic Editor: Jacek Dziok
Copyright © 2013 Pranay Goswami and 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 introduce a new integral operator for meromorphic multivalent functions. The starlikeness condition of this integral operator is determined. Several special cases are also discussed in the form of corollaries.
Let denote the class of all meromorphic functions of the form which are analytic and -valent in the punctured open unit disk where is the open unit disk . In particular, we set .
A function is said to be meromorphic -valent starlike and belongs to the class , if it satisfies the inequality:
A function is said to be meromorphic -valent convex and belongs to the class , if it satisfies the inequality:
We note that In particular, we set for the classes of meromorphic starlike and convex functions, respectively.
Analogous to the integral operator defined by Frasin  on normalized analytic functions, we now define the following general integral operator for the meromorphic -valent functions in the class .
Definition 1. Let , for all and . We introduce a new general integral operator
Remark 2. The integral operator introduced here generalizes the following integral operators.(i)If , then we have the integral operator introduced and studied by Bulut and Goswami .(ii)If , then it reduces to the integral operator (iii)If , then it reduces to the integral operator (iv)For , , , and , it reduces to the new integral operator
The integral operators defined in (ii) and (iii) are introduced and studied by Mohammed and Darus  (also the case in (ii) and (iii) is defined in  and , resp.). Furthermore, the case for the integral operator in (iv) is defined by Bulut and Goswami . For the recent developments on meromorphic functions, refer to [5–10].
For the starlikeness of the integral operator defined in Definition 1, we need to use the following lemma.
Lemma 3 (see ). Let satisfy the following condition: If the function , where , is analytic in and then
2. Starlikeness of the Integral Operator
In this section, we investigate sufficient conditions for the meromorphically starlikeness of the integral operator which is defined in Definition 1.
Theorem 4. Let , for all and . If for all , then the general integral operator defined in Definition 1 belongs to the meromorphic starlike function class .
Proof. For the sake of simplicity, in the proof, we shall write instead of . From (7), it is easy to see that Differentiating the above equality with respect to , we obtain From (16) and (17), we get or equivalently After some calculations, we have We can write the left-hand side of (20) as the following: Now we define a regular function by and . Differentiating (22) logarithmically, we obtain From (21), (22), and (23), we have Let us put From (15), (24) and (25), we get Now we have to show that From (25), we have Thus using Lemma 3, and from (26) and (28), we conclude that , and so that is, the integral operator is a meromorphic multivalent starlike function.
Putting in Theorem 4, we get the following Corollary.
Taking in Theorem 4, we get the following.
Corollary 6. Let , for all and . If for all , then the general integral operator defined in (9) belongs to the meromorphically starlike function class .
Next, putting in Theorem 4, we get the following.
Corollary 8. Let , for all and . If for all , then the general integral operator defined in (10) belongs to the meromorphically starlike function class .
Further taking , , , and in Theorem 4, we have the following.
Corollary 9. Let and . If then the general integral operator defined in (11) belongs to the meromorphically starlike function class .
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