Research Article | Open Access
Huda Al dweby, Maslina Darus, "On Harmonic Meromorphic Functions Associated with Basic Hypergeometric Functions", The Scientific World Journal, vol. 2013, Article ID 164287, 7 pages, 2013. https://doi.org/10.1155/2013/164287
On Harmonic Meromorphic Functions Associated with Basic Hypergeometric Functions
By making use of basic hypergeometric functions, a class of complex harmonic meromorphic functions with positive coefficients is introduced. We obtain some properties such as coefficient inequality, growth theorems, and extreme points.
1. Introduction and Preliminaries
Recently, the popularity of the study of basic hypergeometric series (also called -hypergeometric series) is increasing among the researchers. Back in 1748, Euler considered the infinite product and ever since it became very important to many areas. However, it was stated in the literature that the development of these functions was slower until Heine (1878) converted a simple observation such that , which then returns the theory of basic hypergeometric series to the famous theory of Gauss hypergeometric series. Various authors [1–7] introduced classes of analytic functions involving hypergeometric functions and investigated their properties. However, all these results concern mostly the Gaussian and generalized hypergeometric functions. It seems that no attempt has been made to derive similar results for the basic hypergeometric functions. In this work, we proceed to define a class of harmonic meromorphic functions in the unit disk associated with the basic hypergeometric function and discuss some of its properties.
The subject of harmonic univalent functions is a recent area of research which was initially established by Clunie and Sheil-Small . The importance of these functions is due to their use in the study of minimal surfaces as well as in various problems related to applied mathematics and perhaps to other areas of sciences. Hengartner and Schober  have introduced and studied special classes of harmonic functions, which are defined on the exterior of the unit disk . They have proved that these functions are complex valued harmonic, sense preserving, univalent mappings , admitting the representation where and are analytic in .
We further denote by the subclass of consisting of functions of the form which are univalent harmonic in the punctured unit disk .
A function is said to be in the class of meromorphically harmonic starlike functions in if it satisfies the condition this class has been studied by Jahangiri and Silverman (see ). For harmonic functions the convolution is defined by For complex parameters , , , the basic hypergeometric function is defined as follows: with , where when , , denotes the set of positive integers, and is the -shifted factorial defined by By using the ratio test, one recognizes that if , the series (7) converges absolutely (see ) for all if and for if .
Now for , , and , the basic hypergeometric function defined in (7) takes the form which converges absolutely in the open unit disk .
Let where, for convenience, Corresponding to the function , defined in (12), consider and its inverse function defined by The series expansion of the inverse function is given as where Now, let which is analytic function in the punctured unit disk .
Again, corresponding to the function , defined in (12), consider and its inverse function defined by The series expansion of the inverse function is given as Let which is analytic function in . Now, we define the harmonic meromorphic function as where and are of the forms (18) and (22).
Definition 1. Let denote the family of harmonic meromorphic functions satisfying
for some and for all .
For , , , and , is the class of harmonic meromorphic starlike functions of order and for , , , , and , the class gives the class of harmonic meromorphic starlike functions for all .
2. Main Results
Theorem 2. If is of the form (2) and satisfies the condition where , then is harmonic univalent sense preserving in and .
Proof. Suppose that (27) holds true for . Consider the expression
The inequality in (28) holds true for all . Therefore, letting in (28), we obtain
By hypothesis (27), it follows that (26) holds, so that . Note that is sense preserving in . This is because
Then, we have . Hence the theorem.
Now, we prove that condition (27) is necessary for functions in .
Theorem 3. Let be a function defined by (3). Then, if and only if the inequality is satisfied.
Proof. In view of Theorem 2, it suffices to show that the “only if" part is true. Assume that . Then, Since for all , it follows from (33) that We now choose the values of on the real axis. Upon the clearing the denominator in (34) and letting through real values, we obtain the following: which immediately yields the required condition (32).
Next, we consider a distortion property for functions in the class as follows.
Theorem 4. If defined by (3) is in the class , then for , where , , and , one has
Proof. We will only prove the right-hand inequality. The proof for the left-hand inequality is similar and we will omit it: The functions for show that the bounds given in Theorem 4 are sharp in .
Next, we give the following.
Theorem 5. Set Then, , if and only if, it can be expressed in the form where , , and . In particular, the extreme points of are and .
The work presented here was partially supported by LRGS/TD/2011/UKM/ICT/03/02 and UKM-DLP-2011-050.
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