Certain Properties of -Hypergeometric Functions
The quotients of certain -hypergeometric functions are presented as -fractions which converge uniformly in the unit disc. These results lead to the existence of certain -hypergeometric functions in the class of either -convex functions, , or -starlike functions .
1. Introduction and Preliminaries
Let be the class of analytic functions in the unit disc , normalized by and of the formIn this paper, we extend some results obtained in the theory of functions to the -theory and to achieve this we write out some standard notations and basic definitions used in this paper.
Definition 1. The -shift factorial, the multiple -shift factorial, and the -binomial coefficients are defined bywhere , .
Definition 2. Consider the following:From (3), one has where and as , .
Definition 3. For complex parameters , , and with , , and . denotes the generalized basic (or -) hypergeometric functions
In , Srivastava and Owa summarized some properties of functions that belong to the class of -starlike functions in , introduced and investigated by Ismail et al. in . Srivastava and Owa  further proposed the study of properties of functions that belong to the class of -starlike functions of order , , and also of the functions that belong to the class of -convex functions in . The authors  also defined the class of functions , on the function , as follows:while  defined the class of functions , on the function , asMeanwhile, Agrawal and Sahoo in  defined and studied some properties of functions that belong to the class and also Sahoo and Sharma in  (see also ) defined and studied the class of -close-to-convex functions. Kanas and Răducanu in  also used the Ruscheweyh -differential operator to introduce and study some properties of uniformly starlike functions of order . Other works related to -hypergeometric can also be traced in [10–13].
In addition, in  Baricz and Swaminathan used the Alexander duality between starlike and convex function to define the following.
Definition 4. If is the class of -convex functions, then if and only if . Hence, as , , and reduces to , the class of starlike functions.
Theorem 5. If satisfies the following two more conditions(i),(ii),then
Motivated by the numerous studies, of the abovementioned authors, we aimed, in this paper, at using the parameters , , as real parameters and placing some constraints on quotients of two or more hypergeometric functions to establish the following:(⧫i),(⧫ii). We describe the procedures to achieve (⧫i) as follows:(i)Calculate necessary and sufficient conditions for a function to be in the class .(ii)Calculate suitable, contiguous relations for hypergeometric functions.(iii)Use the contiguous relation to derive equation with a quotient of one or more hypergeometric functions. Let the absolute value of the derived quotient, on the left-hand side of the equation, constrain the function to be in , while the other side of the equation has continued fraction expansion.(iv)Calculate the continued fraction of the hypergeometric quotient on the right-hand side of the equation and convert the continued fractions to a -fraction which converges uniformly.(v)Hence, the -fractions lead to the geometric properties of Pick functions.(vi)Then substituting last result in the third outline with simple calculation on the outcome gives the required results.The description (i) to (vi) can also be used to establish (⧫ii).
First we write out the known results needed to establish ours. Ismail and Libis noted in  that the hypergeometric function satisfies the -difference equationThey rewrite (13) in the formiterated the functional relationship (14), and gotThey also noted that if these iterations converge, this will give rise to the continued fractionwhereThey also modified a result in  to Theorem 6. Later on, we will modify Theorem 6 to suit our results.
Theorem 6 (see ). Let with exception of the zeros of ; the continued fraction of a meromorphic function of , which is equal to the function , is represented bythroughout the -plane with It is equal to this ratio in a neighborhood at origin and furnishes the analytic continuation of it throughout the finite -plane.
We review that the sequence of positive numbers, , , with , is called a Hausdorff moment sequence if there exists a positive (Borel) measure on the close interval such thatEquation (20) can also be represented by with analytic in the slit complex domain , and also belongs to the set of Pick functions.
Lemma 7 bridges the gaps between total monotone sequence, Hausdorff moment sequence, the set of Pick functions, and -fractions.
Lemma 7 (see [14, 20]). Let , be a real sequence; then the following are equivalent:(i), is totally monotone sequence; that is, for , , (ii), is a Hausdorff moment sequence; that is, there exists a positive (Borel) measure on the interval whose sequence of moment is (iii)The power series is analytic in , has the analytic continuation in the complex plane slit , and also has a corresponding -fraction with , , .
For more studies on Hausdorff moment of sequence and hypergeometric mappings see [20–26] and their references. Theorem 8 displays the constraints on the constant that made the -fraction uniformly convergent.
Theorem 8 (see ). Letting be constant satisfying one of the following conditions:(i), (),(ii), (),(iii), (),then the continued fractionconverges uniformly for , ().
Remark 9. By means of equivalence transformation, the continued fraction of the formcan be transformed into continued fraction of the form (25), by first reducing the partial denominator to unity; hence we obtainAlso (10) converges uniformly if there exist constants , such that
We state necessary and sufficient condition for a function to be in the class established in .
Lemma 10 (see ). A function is in the class if and only if
We calculate the necessary and sufficient condition for a function to be in the class .
Lemma 11. A function is in the class if and only if
2. Contiguous Relations and Main Results
In this section we write out some contiguous relations of hypergeometric functions, which can be used to derive a continued fraction expansion, for some quotients of two or more hypergeometric functions. We will also state our results. SupposeRearranging (13), we haveSubstituting the contiguous relation,calculated in  (see also ) in (32) gives
Theorem 12. Let , , , be nonnegative real numbers with and for all . Then hypergeometric quotient with exception of the zeros of has the continued fractionwhere
Theorem 13. If the hypothesis of Theorem 12 holds and(i),(ii) ,(iii) , then the continued fraction (36) can be represented aswhere where is (37) and is (38). Hence the hypergeometric quotient, , converges uniformly.
Theorem 14. If the hypothesis of Theorem 13 holds and there exists an increasing function, , mapping into itself with , then for all . Further,for all .
Theorem 16 (see ). Let , , with nonzeros of . Then continued fraction of a meromorphic function of , , is represented bywhere
Theorem 18. If the hypothesis of Theorem 17 holds and there exists an increasing function, , mapping into itself, with , thenfor all . Also,
Theorem 19. If the hypothesis of Theorem 18 holds, then
3. Proof of the Main Results
Proof of Theorem 12. To calculate the continued fraction of , we let We use the following stated in , to calculate the continued fraction of . Solving (52) giveswhere To calculate , we set Solving (55), we obtainwhere To calculate , we set Assume ; we rewrite (58) aswhere is (37) and is (38). Substituting (56)–(59) in (53), gives the continued fraction (36).
Proof of Theorem 13. To prove Theorem 13, we first reduce the partial denominator of the continued fraction (36) to unity, by setting where with and also Moreover, (36) can be rewritten asAssuming , we transform (64) by replacing with , , , and obtainSince , () and , (65) can be written asHence, by Remark 9, the -fraction of converges uniformly in .
Remark 20. The addition of the leading constant does not affect the convergence of the continued fraction . The continued fraction on the right-hand side of (65) converges to the left-hand side provided belongs to the neighborhood of with and is not a pole of the right-hand side. We also note that the continued fraction (65) is called the infinite -fraction.
Proof of Theorem 14. By Lemma 7(iii), the coefficients in the power series expansion about , of the analytic function, on the left-hand side of the continued fraction (65), are Hausdorff moments of an increasing function, in the open interval with infinitely many points of increase (with total increase less than or equal to 1). Hence, there exists a function mapping to itself, satisfying for and its range contains infinitely many points such thatby analytic continuation, with .
Furthermore, since ,for all .
Proof of Theorem 15. By (35),By Theorem 14, (69) can be written asFor to be in , we show thatwhere .
Applying the triangle inequality to the left-hand side of (71), with , we obtain where By hypothesis of Theorem 15 and , we need to show that . Hence, Theorem 15 is established.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
The work presented here was fully supported by AP-2013-009.
H. M. Srivastava and S. Owa, Univalent Functions, Fractional Calculus, and Their Applications, Halsted Press, Ellis Horwood Limited, Chichester, UK; John Wiley & Sons, New York, NY, USA, 1989.
M. E. H. Ismail, E. Merkes, and D. Styer, “A generalization of stalike functions,” Complex Variables, Theory and Application, vol. 14, pp. 77–84, 1990.View at: Google Scholar
S. K. Sahoo and N. L. Sharma, “On a generalization of close-to-convex functions,” Annales Polonici Mathematici, vol. 113, no. 17, pp. 93–108, 2015.View at: Google Scholar
K. Raghavendar and A. Swaminathan, “Close-to-convexity of basic hypergeometric functions using their Taylor coefficients,” Journal of Mathematics and Applications, vol. 35, pp. 111–125, 2012.View at: Google Scholar
G. Murugusundaramoorthy, T. Janani, and M. Darus, “Coefficient estimate of biunivalent functions based on q-hypergeometric functions,” Applied Sciences, vol. 17, pp. 75–85, 2015.View at: Google Scholar
H. Aldweby and M. Darus, “Properties of a subclass of analytic functions defined by generalized operator involving q-hypergeometric function,” Far East Journal of Mathematical Sciences, vol. 81, no. 2, pp. 189–200, 2013.View at: Google Scholar
A. Mohammed and M. Darus, “A generalized operator involving the q-hypergeometric function,” Matematicki Vesnik, vol. 65, no. 4, pp. 454–465, 2012.View at: Google Scholar
H. S. Wall, Analytic Theory of Continued Fractions, D. Van Nostrand Company, New York, NY, USA, 1948.View at: MathSciNet
J.-G. Liu and R. L. Pego, “On generating functions of Hausdorff moment sequences,” Transactions of the American Mathematical Society, In press.View at: Google Scholar
R. Küstner, “Hypergeometric functions and convolutions of starlike or convex functions of order α,” Computational Methods and Function Theory, vol. 2, no. 2, pp. 597–610, 2002.View at: Google Scholar
G. Pólya, “Application of theorem connected with the problem of moments,” Messenger of Mathematics, vol. 55, pp. 189–192, 1925/1926.View at: Google Scholar