American Journal of Mathematics and Statistics

p-ISSN: 2162-948X    e-ISSN: 2162-8475

2013;  3(6): 301-304

doi:10.5923/j.ajms.20130306.01

Some Subordination Results for Certain Subclasses of Analytic Functions Defined by Using Salagean Operator

Oyekan E. A.1, Opoola T. O.2

1Department of Mathematics and Statistics, Bowen University, Iwo, 23001, Nigeria

2Department Mathematics, University of Ilorin, Ilorin, 240001, Nigeria

Correspondence to: Oyekan E. A., Department of Mathematics and Statistics, Bowen University, Iwo, 23001, Nigeria.

Email:

Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved.

Abstract

Functions belonging to each of the subclasses and of normalized analytic functions in the open unit disk are investigated when and several subordinations are obtained. A number of interesting consequences of these subordination results are also discussed.

Keywords: Subordination, Analytic Functions, Salagean Operator, Subordinating Factor Sequence, Hadamard Product (or Convolution)

Cite this paper: Oyekan E. A., Opoola T. O., Some Subordination Results for Certain Subclasses of Analytic Functions Defined by Using Salagean Operator, American Journal of Mathematics and Statistics, Vol. 3 No. 6, 2013, pp. 301-304. doi: 10.5923/j.ajms.20130306.01.

1. Introduction and Definitions

Let denote the class of functions of the form
(1.1)
Which are analytic in the unit disk
Shu-Hai and Tang in 2010[1], introduced the classes and gave the following definition:
Definition 1. Let denote the subclass of consisting of functions which satisfy the following inequality:
(1.2)
Definition 2. Let be the subclass of consisting of function which satisfy the following condition:
(1.3)
Where is the Salagean derivative operator defined as:
For it is easy to see that
We denote by k the class of convex functions i.e.
Definition 3. (Hadamard product or convolution) Given two functions and where is as defined in (1.1) and is given by
(1.4)
The Hadamard product (or convolution) of and is defined by
(1.5)
Definition 4. (Subordination principle)
Let and be analytic in the unit disk . Then is said to be subordinate to in and we write , if there exists a Schwarz function , analytic in with such that
(1.6)
In particular, if the function is univalent in , then is subordinate to if
(1.7)
Definition 5. (Subordinating factor sequence)
A sequence of complex numbers is said to be a subordinating factor sequence if whenever of the form (1.1) is analytic, univalent and convex in , the subordination is given by
We have the following theorem
Theorem 1.1 (Wilf [3])
The sequence is a subordinating factor sequence if and only if
(1.8)
Theorem 1.2. [1]
(1.9)
(1.10)
Theorem 1.3. [1]
(1.11)
(1.12)
In view of Theorem 1.2 and Theorem 1.3, we now introduce the subclasses and which consist of functions whose Taylor-Maclaurin coefficients satisfy the inequalities (1.9) and (1.11) respectively.
In our proposed investigation of functions in the classes and we obtain sharp subordination results for these classes and also investigate some applications of the main results which give important results of analytic functions.

2. Main Theorem

Subordination results for the class
Theorem 2.1. Let
(2.1)
(2.2)
(2.3)
(2.4)
PROOF OF THEOREM 2.1
Let defined by (1.1) be any member of the class and suppose that
Then
(2.5)
Thus, by Definition 5 the subordination (2.2) will hold if the sequence,
(2.6)
is a subordinating factor sequence with .
Therefore by Theorem 1.1, it is sufficient to show that
(2.7)
Now,
(2.8)
because is an increasing function of
Thus,
(2.9)
Thus, (2.4) holds true in U and consequently proves (2.2).
Next we show that
Now taking
and in (2.2) we have that
(2.10)
Therefore since
(2.11)
which implies that
(2.12)
Hence, we have
For
(2.13)
By max/min principle
(2.14)
(2.15)
Hence,
(2.16)
(2.17)
which shows that the constant
is the best possible and thus complete the proof of theorem 2.1.
Subordination result for the class
Our proof of Theorem 2.2 below is much akin to that of Theorem 2.1. Here we make use of Theorem 1.3 in place of Theorem 1.2 and let
Theorem 2.2. Let
(2.18)
(2.19)
(2.20)
(2.21)

3. Some Applications

Taking in Theorem 2.1; we obtain the following:
Corollary1.
(3.1)
(3.2)
(3.3)
Remark 1:
and Karthikenyan[5], and singh[6]
Corollary2.
(3.4)
(3.5)
(3.6)
Remark 2:
The case and was obtained by Frasin [4], and Selvaraj and Karthikeyan [5].and Karthikeyan [5]
(3.7)

References

[1]  Shu – Hai Li and Tang, H., “Certain New Classes of analytic Functions defined by using Salagean operator,” Bulletin of Mathematical Analysis and Applications, Vol. 2, Issue 4, pp. 62-75, 2010.
[2]  S˘al˘agean, G..S., “Subclasses of univalent functions,” Lecture Notes in Math. Springer-Verlag,” 1013, pp. 362–372, 1983.
[3]  Wilf, H.S. “Subordinating factor sequences for some convex maps of unit circle,” Proceedings of the American Mathematical society, Vol. 12, pp. 689-693, 1961.
[4]  Frasin, B.A., “Subordination results for class of analytic functions defined by a linear operator,” Journal of Inequalities in Pure and Applied Mathematics, Vol. 7. Issue 4, Article 134, pp 1-7, 2006.
[5]  Selvaraj, C. and karthikeyan, K.R., “Certain Subordination Results for a Class of Analytic Functions Defined by a Generalized Integral Operator, International Journal of Computational and mathematical Sciences, 2, pp 166-168, 2008.
[6]  Sukhjit Singh, “A Subordination Theorem for Spiral-like Functions,” International Journal of Mathematics and mathematical Sci., Vol. 24, No 7, pp. 433-435, 2000.