Research Article | Open Access

Serap Bulut, "Inclusion and Neighborhood Properties for Certain Classes of Multivalently Analytic Functions", *Journal of Complex Analysis*, vol. 2013, Article ID 754598, 5 pages, 2013. https://doi.org/10.1155/2013/754598

# Inclusion and Neighborhood Properties for Certain Classes of Multivalently Analytic Functions

**Academic Editor:**Lianzhong Yang

#### Abstract

We introduce and investigate two new general subclasses of multivalently analytic functions of complex order by making use of the familiar convolution structure of analytic functions. Among the various results obtained here for each of these function classes, we derive the coefficient inequalities and other interesting properties and characteristics for functions belonging to the classes introduced here.

#### 1. Introduction and Definitions

Let be the set of real numbers, let be the set of complex numbers, let be the set of positive integers, and let .

Let denote the class of functions of the form which are analytic and -valent in the open unit disk

Denote by the Hadamard product (or convolution) of the functions and ; that is, if is given by (1) and is given by then

*Definition 1. *Let the function . Then one says that is in the class if it satisfies the condition
where
is given by (3), and denotes the falling factorial defined as follows:

Various special cases of the class were considered by many earlier researchers on this topic of *Geometric Function Theory*. For example, reduces to the function class(i) for , and , studied by Mostafa and Aouf [1];(ii)for and , studied by Srivastava et al. [2];(iii) for , and , studied by Prajapat et al. [3];(iv) for , and , studied by Srivastava and Bulut [4];(v)for , , , and , studied by Ali et al. [5].

*Definition 2. *Let the function . Then one says that is in the class if it satisfies the condition
where and are defined by (3) and (6), respectively.

Setting , in Definition 2, we have the special class (which generalizes the class defined by Prajapat et al. [3]) introduced by Srivastava et al. [2].

Following a recent investigation by Frasin and Darus [6], if and , then we define the -neighborhood of the function by

It follows from the definition (9) that if then

The main object of this paper is to investigate the various properties and characteristics of functions belonging to the above-defined classes Apart from deriving coefficient bounds and coefficient inequalities for each of these classes, we establish several inclusion relationships involving the -neighborhoods of functions belonging to the general classes which are introduced above.

#### 2. Coefficient Bounds and Coefficient Inequalities

We begin by proving a necessary and sufficient condition for the function to be in each of the classes

Theorem 3. *Let the function be given by (1). Then is in the class if and only if
**
where
*

*Proof. *We first suppose that the function given by (1) is in the class . Then, in view of (3)–(6), we have
or equivalently
If we choose to be real and let , we arrive easily at the inequality (14).

Conversely, we suppose that the inequality (14) holds true and let
Then, we find that
Hence, by the Maximum Modulus Theorem, we have
which evidently completes the proof of Theorem 3.

*Remark 4. *If we set and in Theorem 3, then we have [2, Theorem 1].

Lemma 5. *Let the function given by (1) be in the class . Then, for , one has
**
where is defined by (15).*

*Proof. * Let *.* Then, in view of the assertion (14), we have
Furthermore, by rewriting the assertion (14) as follows:
we obtain

Similar to Theorem 3, we can prove the following result.

Theorem 6. *Let the function be given by (1). Then is in the class if and only if
**
where is defined by (15).*

*Remark 7. *If we set and in Theorem 6, then we have [2, Theorem 2].

Lemma 8. *Let the function given by (1) be in the class . Then, for , one has
**
where is defined by (15).*

*Proof. *Let *.* Then, in view of the assertion (26), we have
Furthermore, we also have from the assertion (26)

#### 3. A Set of Inclusion Relationships

In this section, we determine inclusion relations for the classes involving -neighborhoods defined by (9) and (11).

Theorem 9. *If and
**
then
**
where and are given by (10) and (15), respectively. *

*Proof. *The inclusion relation (33) would follow readily from the definition (11) and the assertion (22).

*Remark 10. *If we set and in Theorem 9, then we have [2, Theorem 3].

Theorem 11. *If and
**
then
**
where and are given by (10) and (15), respectively. *

*Proof. *The inclusion relation (35) would follow readily from the definition (11) and the assertion (28).

*Remark 12. * If we set and in Theorem 11, then we have [2, Theorem 4].

#### 4. Neighborhood Properties

In this section, we determine the neighborhood properties for each of the function classes which are defined as follows.

*Definition 13. *A function is said to be in the class if there exists a function such that

*Definition 14. *A function is said to be in the class if there exists a function such that the inequality (37) holds true.

Setting in Definitions 13 and 14, we have the special classes introduced by Srivastava et al. [2], respectively.

Theorem 15. *If and
**
then
**
where is defined by (15).*

*Proof. *Suppose that *.* Then we find from (9) that
which readily implies that
Since , we find from (21) that
so that
where is given by (39). Thus, by Definition 13, . This completes the proof of Theorem 15.

*Remark 16. *If we set and in Theorem 15, then we have [2, Theorem 5].

The proof of Theorem 17 (based upon Definition 14) is similar to that of Theorem 15. Therefore we omit the details involved.

Theorem 17. *If and
**
then
**
where is defined by (15).*

*Remark 18. *If we set and in Theorem 17, then we have [2, Theorem 6].

#### Acknowledgment

The present investigation was supported by the Kocaeli University under Grant HD 2011/22.

#### References

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#### Copyright

Copyright © 2013 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.