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On Convergence of -Series Involving Basic Hypergeometric Series
Journal of Inequalities and Applications volume 2009, Article number: 170526 (2009)
Abstract
We use inequality technique and the terminating case of the -binomial formula to give some results on convergence of -series involving basic hypergeometric series. As an application of the results, we discuss the convergence for special Thomae -integral.
1. Introduction
-Series, which are also called basic hypergeometric series, play a very important role in many fields, such as affine root systems, Lie algebras and groups, number theory, orthogonal polynomials and physics. Convergence of a -series is an important problem in the study of -series. There are some results about it in [1–3]. For example, Ito used inequality technique to give a sufficient condition for convergence of a special -series called Jackson integral. In this paper, by using inequality technique, we derive the following two theorems on convergence of -series involving basic hypergeometric series, which can be used for convergence of special Thomae -integral.
2. Notations and Known Results
We recall some definitions, notations, and known results which will be used in the proofs. Throughout this paper, it is supposed that . The -shifted factorials are defined as
We also adopt the following compact notation for multiple -shifted factorials:
where is an integer or .
The -binomial theorem [4, 5] is
When , where denotes a nonnegative integer
Heine introduced the basic hypergeometric series, which is defined by [4, 5]
3. Main Results
The main purpose of the present paper is to establish the following two theorems on convergence of -series involving basic hypergeometric series.
Theorem 3.1.
Suppose , are any real numbers such that and with . Let be any sequence of numbers. If
then the -series
converges absolutely.
Proof.
Let and
It is easy to see that is a monotone function with respect to .
Consequently, one has
From (3.4), one knows
where for .
So, one has
It is obvious that
Multiplying both sides of (3.6) by
gives
Hence,
By using (2.4) one obtains
Substituting (3.11) into (3.10), one has
Multiplying both sides of (3.12) by , one has
The ratio test shows that the series
is absolutely convergent. From (3.13), it is sufficient to establish that (3.2) is absolutely convergent.
Theorem 3.2.
Suppose are any real numbers such that and with . Let be any sequence of numbers. If
then the -series
diverges.
Proof.
Let , and
It is easy to see that is a monotone function with respect to .
Consequently, one has
From (3.18), one knows
where for .
So, one has
It is obvious that
Multiplying both sides of (3.20) by
gives
Hence,
By using (2.4) one obtains
Substituting (3.25) into (3.24), one has
Multiplying both sides of (3.26) by , one has
Since
By hypothesis
therefore, in both cases there exists a integer such that
So, one can conclude that
Now, from (3.27) and (3.31)
Thereby, (3.16) diverges.
We want to point out that some -integral can be written as (3.2) or (3.16). So, the results obtained here can be used to discuss the convergence of -integrals.
4. Some Applications
In [6, 7], Thomae defined the -integral on the interval by
The right side of (4.1) corresponds to use a Riemann sum with partition points Jackson [8] extended Thomae -integral via
In this section, we use the theorems derived in this paper to discuss two examples of the convergence for Thomae -integral. We have the following theorems.
Theorem 4.1.
Let be any real numbers such that and with . If , then the Thomae -integral
converges absolutely.
Proof.
By the definition of Thomae -integral (4.1), one has
Using Theorem 3.1 and noticing,
one knows that (4.3) converges absolutely.
Theorem 4.2.
Let ,  be any real numbers such that and with . If , then the Thomae -integral
diverges.
Proof.
By the definition of Thomae -integral (4.1), one has
Using Theorem 3.2 and noticing,
one knows that (4.6) diverges.
References
Ito M: Convergence and asymptotic behavior of Jackson integrals associated with irreducible reduced root systems. Journal of Approximation Theory 2003,124(2):154–180. 10.1016/j.jat.2003.08.006
Wang M: An inequality for and its applications. Journal of Mathematical Inequalities 2007,1(3):339–345.
Wang M: Two inequalities for and applications. Journal of Inequalities and Applications 2008, 2008:-6.
Andrews GE: The Theory of Partitions, Encyclopedia of Mathematics and Its Applications. Volume 2. Addison-Wesley, Reading, Mass, USA; 1976:xiv+255.
Gasper G, Rahman M: Basic Hypergeometric Series, Encyclopedia of Mathematics and Its Applications. Volume 35. Cambridge University Press, Cambridge, Mass, USA; 1990:xx+287.
Thomae J: Beiträge zur Theorie der durch die Heine'sche Reihe darstellbaren Funktionen. Journal für die reine und angewandte Mathematik 1869, 70: 258–281.
Thomae J: Les séries Heinéennes supérieures, ou les séries de la forme . Annali di Matematica Pura ed Applicata 1870, 4: 105–138.
Jackson FH: On -definite integrals. Quarterly Journal of Pure and Applied Mathematics 1910, 50: 101–112.
Acknowledgment
The authors would like to express deep appreciation to the referees for the helpful suggestions. In particular, the authors thank the referees for help to improve the presentation of the paper. Mingjin Wang was supported by STF of Jiangsu Polytechnic University.
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Wang, M., Zhao, X. On Convergence of -Series Involving Basic Hypergeometric Series. J Inequal Appl 2009, 170526 (2009). https://doi.org/10.1155/2009/170526
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DOI: https://doi.org/10.1155/2009/170526