Abstract
Subordination and superordination preserving properties for multivalent functions in the open unit disk associated with the Dziok-Srivastava operator are derived. Sandwich-type theorems for these multivalent functions are also obtained.
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1. Introduction
Let be the open unit disk in the complex plane , and let denote the class of analytic functions defined in For and , let consist of functions of the form . Let and be members of . The function is said to be subordinate to , or is said to be superordinate to , if there exists a function analytic in , with and such that . In such a case, we write or . If the function is univalent in , then if and only if and (cf. [1, 2]). Let , and let be univalent in . The subordination is called a first-order differential subordination. It is of interest to determine conditions under which arises for a prescribed univalent function . The theory of differential subordination in is a generalization of a differential inequality in , and this theory of differential subordination was initiated by the works of Miller, Mocanu, and Reade in 1981. Recently, Miller and Mocanu [3] investigated the dual problem of differential superordination. The monograph by Miller and Mocanu [1] gives a good introduction to the theory of differential subordination, while the book by Bulboacă [4] investigates both subordination and superordination. Related results on superordination can be found in [5–23].
By using the theory of differential subordination, various subordination preserving properties for certain integral operators were obtained by Bulboacă [24], Miller et al. [25], and Owa and Srivastava [26]. The corresponding superordination properties and sandwich-type results were also investigated, for example, in [4]. In the present paper, we investigate subordination and superordination preserving properties of functions defined through the use of the Dziok-Srivastava linear operator (see (1.9) and (1.10)), and also obtain corresponding sandwich-type theorems.
The Dziok-Srivastava linear operator is a particular instance of a linear operator defined by convolution. For , let denote the class of functions
that are analytic and -valent in the open unit disk with . The Hadamard product (or convolution) of two analytic functions
is defined by the series
For complex parameters and , the generalized hypergeometric function is given by
where is the Pochhammer symbol (or the shifted factorial) defined (in terms of the Gamma function) by
To define the Dziok-Srivastava operator
via the Hadamard product given by (1.3), we consider a corresponding function
defined by
The Dziok-Srivastava linear operator is now defined by the Hadamard product
This operator was introduced and studied in a series of recent papers by Dziok and Srivastava ([27–29]; see also [30, 31]). For convenience, we write
The importance of the Dziok-Srivastava operator from the general convolution operator rests on the relation
that can be verified by direct calculations (see, e.g., [27]). The linear operator includes various other linear operators as special cases. These include the operators introduced and studied by Carlson and Shaffer [32], Hohlov ([33], also see [34, 35]), and Ruscheweyh [36], as well as works in [27, 37].
2. Definitions and Lemmas
Recall that a domain is convex if the line segment joining any two points in lies entirely in , while the domain is starlike with respect to a point if the line segment joining any point in to lies inside . An analytic function is convex or starlike if is, respectively, convex or starlike with respect to 0. For , analytically, these functions are described by the conditions or , respectively. More generally, for , the classes of convex functions of order and starlike functions of order are, respectively, defined by or . A function is close-to-convex if there is a convex function (not necessarily normalized) such that . Close-to-convex functions are known to be univalent.
The following definitions and lemmas will also be required in our present investigation.
Definition 2.1 (see [1, page 16]).
Let , and let be univalent in . If is analytic in and satisfies the differential subordination
then is called a solution of differential subordination (2.1). A univalent function is called a dominant of the solutions of differential subordination (2.1), or more simply a dominant, if for all satisfying (2.1). A dominant that satisfies for all dominants of (2.1) is said to be the best dominant of (2.1).
Definition 2.2 (see [3, Definition 1, pages 816-817]).
Let , and let be analytic in . If and are univalent in and satisfy the differential superordination
then is called a solution of differential superordination (2.2). An analytic function is called a subordinant of the solutions of differential superordination (2.2), or more simply a subordinant, if for all satisfying (2.2). A univalent subordinant that satisfies for all subordinants of (2.2) is said to be the best subordinant of (2.2).
Definition 2.3 (see [1, Definition 2.2b, page 21]).
Denote by the class of functions that are analytic and injective on , where
and are such that for .
Lemma 2.4 (cf. [1, Theorem 2.3i, page 35]).
Suppose that the function satisfies the condition
for all real and , where is a positive integer. If the function is analytic in and
then in .
One of the points of importance of Lemma 2.4 was its use in showing that every convex function is starlike of order 1/2 (see e.g., [38, Theorem 2.6a, page 57]). In this paper, we take an opportunity to use the technique in the proof of Theorem 3.1.
Lemma 2.5 (see [39, Theorem 1, page 300]).
Let with , and let with . If for , then the solution of the differential equation
with is analytic in and satisfies .
Lemma 2.6 (see [1, Lemma 2.2d, page 24]).
Let with , and let be analytic in with and . If is not subordinate to , then there exists points and , for which ,
A function defined on is a subordination chain (or Löwner chain) if is analytic and univalent in for all , is continuously differentiable on for all , and for .
Lemma 2.7 (see [3, Theorem 7, page 822]).
Let , , and set . If is a subordination chain and , then
implies that
Furthermore, if has a univalent solution , then is the best subordinant.
Lemma 2.8 (see [3, Lemma B, page 822]).
The function , with and , is a subordination chain if and only if
3. Main Results
We first prove the following subordination theorem involving the operator defined by (1.10).
Theorem 3.1.
Let . For , , let
Suppose that
where
Then the subordination condition
implies that
Moreover, the function is the best dominant.
Proof.
Let us define the functions and , respectively, by
We first show that if the function is defined by
then
Logarithmic differentiation of both sides of the second equation in (3.6) and using (1.11) for yield
Now, differentiating both sides of (3.9) results in the following relationship:
We also note from (3.2) that
and, by using Lemma 2.5, we conclude that differential equation (3.10) has a solution with . Let us put
where is given by (3.3). From (3.2), (3.10), and (3.12), it follows that
In order to use Lemma 2.4, we now proceed to show that for all real and . Indeed, from (3.12),
where
For given by (3.3), we can prove easily that the expression given by (3.15) is positive or equal to zero. Hence, from (3.14), we see that for all real and . Thus, by using Lemma 2.4, we conclude that for all . That is, defined by (3.6) is convex in . Next, we prove that subordination condition (3.4) implies that
for the functions and defined by (3.6). Without loss of generality, we also can assume that is analytic and univalent on and for . For this purpose, we consider the function given by
Note that
This shows that the function
satisfies the condition for all . Furthermore,
Therefore, by virtue of Lemma 2.8, is a subordination chain. We observe from the definition of a subordination chain that
Now suppose that is not subordinate to ; then, by Lemma 2.6, there exist points and such that
Hence,
by virtue of subordination condition (3.4). This contradicts the above observation that . Therefore, subordination condition (3.4) must imply the subordination given by (3.16). Considering , we see that the function is the best dominant. This evidently completes the proof of Theorem 3.1.
We next prove a dual result to Theorem 3.1, in the sense that subordinations are replaced by superordinations.
Theorem 3.2.
Let . For , , let
Suppose that
where is given by (3.3). Further, suppose that
is univalent in and . Then the superordination
implies that
Moreover, the function is the best subordinant.
Proof.
The first part of the proof is similar to that of Theorem 3.1 and so we will use the same notation as in the proof of Theorem 3.1.
Now let us define the functions and , respectively, by (3.6). We first note that if the function is defined by (3.7), then (3.9) becomes
After a simple calculation, (3.29) yields the relationship
Then by using the same method as in the proof of Theorem 3.1, we can prove that for all . That is, defined by (3.6) is convex (univalent) in . Next, we prove that the subordination condition (3.27) implies that
for the functions and defined by (3.6). Now considering the function defined by
we can prove easily that is a subordination chain as in the proof of Theorem 3.1. Therefore according to Lemma 2.7, we conclude that superordination condition (3.27) must imply the superordination given by (3.31). Furthermore, since the differential equation (3.29) has the univalent solution , it is the best subordinant of the given differential superordination. This completes the proof of Theorem 3.2.
Combining Theorems 3.1 and 3.2, we obtain the following sandwich-type theorem.
Theorem 3.3.
Let . For , , , let
Suppose that
where is given by (3.2). Further, suppose that
is univalent in and . Then
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
The assumption of Theorem 3.3 that the functions
need to be univalent in may be replaced by another condition in the following result.
Corollary 3.4.
Let . For , , let
and , be as in (3.33). Suppose that condition (3.34) is satisfied and
where is given by (3.3). Then
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
Proof.
In order to prove Corollary 3.4, we have to show that condition (3.40) implies the univalence of and
Since given by (3.3) in Theorem 3.1 satisfies the inequality , condition (3.40) means that is a close-to-convex function in (see [40]) and hence is univalent in . Furthermore, by using the same techniques as in the proof of Theorem 3.1, we can prove the convexity (univalence) of and so the details may be omitted. Therefore, from Theorem 3.3, we obtain Corollary 3.4.
By taking ,,, , and in Theorem 3.3, we have the following result.
Corollary 3.5.
Let . Let
Suppose that
and is univalent in and . Then
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
Next consider the generalized Libera integral operator defined by (cf. [37, 41–43])
For the choice , with , (3.48) reduces to the well-known Bernardi integral operator [41]. The following is a sandwich-type result involving the generalized Libera integral operator .
Theorem 3.6.
Let . Let
Suppose that
where
If is univalent in and , then
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
Proof.
Let us define the functions and by
respectively. From the definition of the integral operator given by (3.48), it follows that
Then, from (3.49) and (3.55),
Setting
and differentiating both sides of (3.51) result in
The remaining part of the proof is similar to that of Theorem 3.3 (a combined proof of Theorems 3.1 and 3.2) and is therefore omitted.
By using the same methods as in the proof of Corollary 3.4, the following result is obtained.
Corollary 3.7.
Let and
Suppose that condition (3.50) is satisfied and
where is given by (3.51). Then
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
Taking ,, , and in Corollary 3.7, we have the following result.
Corollary 3.8.
Let . Let
Suppose that
where is given by (3.51), and is univalent in and . Then,
implies that
Moreover, the functions and are the best subordinant and the best dominant, respectively.
References
Miller SS, Mocanu PT: Differential Subordinations, Monographs and Textbooks in Pure and Applied Mathematics. Volume 225. Marcel Dekker, New York, NY, USA; 2000:xii+459.
Srivastava HM, Owa S (Eds): Current Topics in Analytic Function Theory. World Scientific, River Edge, NJ, USA; 1992:xiv+456.
Miller SS, Mocanu PT: Subordinants of differential superordinations. Complex Variables. Theory and Application 2003,48(10):815–826.
Bulboacă T: Differential Subordinations and Superordinations: New Results. House of Science Book Publ., Cluj-Napoca, Romania; 2005.
Ali RM, Ravichandran V, Seenivasagan N: Subordination and superordination of the Liu-Srivastava linear operator on meromorphic functions. Bulletin of the Malaysian Mathematical Sciences Society 2008,31(2):193–207.
Ali RM, Ravichandran V, Seenivasagan N: Subordination and superordination on Schwarzian derivatives. Journal of Inequalities and Applications 2008, 2008:-18.
Ali RM, Ravichandran V, Seenivasagan N: Differential subordination and superordination of analytic functions defined by the multiplier transformation. Mathematical Inequalities & Applications 2009,12(1):123–139.
Ali RM, Ravichandran V, Seenivasagan N: On subordination and superordination of the multiplier transformation for meromorphic functions. Bulletin of the Malaysian Mathematical Sciences Society 2010,33(2):311–324.
Ali RM, Ravichandran V, Seenivasagan N: Differential subordination and superordination of analytic functions defined by the Dziok-Srivastava linear operator. Journal of The Franklin Institute 2010,347(9):1762–1781. 10.1016/j.jfranklin.2010.08.009
Ali RM, Ravichandran V, Khan MH, Subramanian KG: Differential sandwich theorems for certain analytic functions. Far East Journal of Mathematical Sciences (FJMS) 2004,15(1):87–94.
Ali RM, Ravichandran V, Khan MH, Subramanian KG: Applications of first order differential superordinations to certain linear operators. Southeast Asian Bulletin of Mathematics 2006,30(5):799–810.
Ali RM, Ravichandran V: Classes of meromorphic -convex functions. Taiwanese Journal of Mathematics 2010,14(4):1479–1490.
Bulboacă T: A class of superordination-preserving integral operators. Indagationes Mathematicae 2002,13(3):301–311. 10.1016/S0019-3577(02)80013-1
Bulboacă T: Classes of first-order differential superordinations. Demonstratio Mathematica 2002,35(2):287–292.
Bulboacă T: Generalized Briot-Bouquet differential subordinations and superordinations. Revue Roumaine de Mathématiques Pures et Appliquées 2002,47(5–6):605–620.
Bulboacă T: Sandwich-type theorems for a class of integral operators. Bulletin of the Belgian Mathematical Society. Simon Stevin 2006,13(3):537–550.
Cho NE, Srivastava HM: A class of nonlinear integral operators preserving subordination and superordination. Integral Transforms and Special Functions 2007,18(1–2):95–107.
Cho NE, Kwon OS, Owa S, Srivastava HM: A class of integral operators preserving subordination and superordination for meromorphic functions. Applied Mathematics and Computation 2007,193(2):463–474. 10.1016/j.amc.2007.03.084
Cho NE, Kim IH: A class of integral operators preserving subordination and superordination. Journal of Inequalities and Applications 2008, 2008:-14.
Cho NE, Kwon OS: A class of integral operators preserving subordination and superordination. Bulletin of the Malaysian Mathematical Sciences Society 2010,33(3):429–437.
Kwon OS, Cho NE: A class of nonlinear integral operators preserving double subordinations. Abstract and Applied Analysis 2008, 2008:-10.
Miller SS, Mocanu PT: Briot-Bouquet differential superordinations and sandwich theorems. Journal of Mathematical Analysis and Applications 2007,329(1):327–335. 10.1016/j.jmaa.2006.05.080
Xiang R-G, Wang Z-G, Darus M: A family of integral operators preserving subordination and superordination. Bulletin of the Malaysian Mathematical Sciences Society 2010,33(1):121–131.
Bulboacă T: Integral operators that preserve the subordination. Bulletin of the Korean Mathematical Society 1997,34(4):627–636.
Miller SS, Mocanu PT, Reade MO: Subordination-preserving integral operators. Transactions of the American Mathematical Society 1984,283(2):605–615. 10.1090/S0002-9947-1984-0737887-4
Owa S, Srivastava HM: Some subordination theorems involving a certain family of integral operators. Integral Transforms and Special Functions 2004,15(5):445–454. 10.1080/10652460410001727563
Dziok J, Srivastava HM: Classes of analytic functions associated with the generalized hypergeometric function. Applied Mathematics and Computation 1999,103(1):1–13.
Dziok J, Srivastava HM: Some subclasses of analytic functions with fixed argument of coefficients associated with the generalized hypergeometric function. Advanced Studies in Contemporary Mathematics 2002,5(2):115–125.
Dziok J, Srivastava HM: Certain subclasses of analytic functions associated with the generalized hypergeometric function. Integral Transforms and Special Functions 2003,14(1):7–18. 10.1080/10652460304543
Liu J-L, Srivastava HM: Certain properties of the Dziok-Srivastava operator. Applied Mathematics and Computation 2004,159(2):485–493. 10.1016/j.amc.2003.08.133
Liu J-L, Srivastava HM: Classes of meromorphically multivalent functions associated with the generalized hypergeometric function. Mathematical and Computer Modelling 2004,39(1):21–34. 10.1016/S0895-7177(04)90503-1
Carlson BC, Shaffer DB: Starlike and prestarlike hypergeometric functions. SIAM Journal on Mathematical Analysis 1984,15(4):737–745. 10.1137/0515057
Hohlov JuE: Operators and operations on the class of univalent functions. Izvestiya Vysshikh Uchebnykh Zavedeniĭ. Matematika 1978, 10 (197): 83–89.
Saitoh H: A linear operator and its applications of first order differential subordinations. Mathematica Japonica 1996,44(1):31–38.
Srivastava HM, Owa S: Some characterization and distortion theorems involving fractional calculus, generalized hypergeometric functions, Hadamard products, linear operators, and certain subclasses of analytic functions. Nagoya Mathematical Journal 1987, 106: 1–28.
Ruscheweyh S: New criteria for univalent functions. Proceedings of the American Mathematical Society 1975, 49: 109–115. 10.1090/S0002-9939-1975-0367176-1
Owa S, Srivastava HM: Some applications of the generalized Libera integral operator. Proceedings of the Japan Academy, Series A 1986,62(4):125–128.
Miller SS, Mocanu PT: Differential subordinations and univalent functions. The Michigan Mathematical Journal 1981,28(2):157–172.
Miller SS, Mocanu PT: Univalent solutions of Briot-Bouquet differential equations. Journal of Differential Equations 1985,56(3):297–309. 10.1016/0022-0396(85)90082-8
Kaplan W: Close-to-convex schlicht functions. The Michigan Mathematical Journal 1952, 1: 169–185.
Bernardi SD: Convex and starlike univalent functions. Transactions of the American Mathematical Society 1969, 135: 429–446.
Goel RM, Sohi NS: A new criterion for -valent functions. Proceedings of the American Mathematical Society 1980,78(3):353–357.
Libera RJ: Some classes of regular univalent functions. Proceedings of the American Mathematical Society 1965, 16: 755–758. 10.1090/S0002-9939-1965-0178131-2
Acknowledgments
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (no. 2010-0017111) and grants from Universiti Sains Malaysia and University of Delhi. The authors are thankful to the referees for their useful comments.
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Cho, N.E., Kwon, O.S., Ali, R.M. et al. Subordination and Superordination for Multivalent Functions Associated with the Dziok-Srivastava Operator. J Inequal Appl 2011, 486595 (2011). https://doi.org/10.1155/2011/486595
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DOI: https://doi.org/10.1155/2011/486595