q-functions of several variables

We begin with the vector notation for the most important functions and q-Taylor formulas for power series and functions of inverse q-shifted factorials. We continue with a historical introduction to the rest of this long and interesting chapter and to the

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q-functions of several variables

Symmetries correspond to the q-functions of many variables. SO(3) q-Appell functions SU(2) q-Lauricella functions As molecules strive for the configuration with the greatest symmetry, our transformations are often symmetrical. The multiple q-hypergeometric functions are defined by the q-shifted factorial and the tilde operator. By our method we are able to find q-analogues of corresponding formulas for the multiple hypergeometric case, which elucidate the integration properties of q-calculus and helps in trying to make a first systematic attempt to find summation and reduction theorems for multiple basic series, including the Jackson q function. We give two definitions of the generalized q-Kampé de Fériet function, in the spirit of Karlsson and Srivastava [482], which are symmetric in the variables and allow us to treat q as a vector. Various connections between transformation formulas for multiple q-hypergeometric series and Lie algebras and finite groups known from the literature are cited.

10.1 The corresponding vector notation Definition 162 We define vector versions of powers, q-shifted factorials, q-Pochhammer symbols and JHC q-additions, as follows: α

x ≡

n 

α

xj j ,

(10.1)

j =1

 1 1 ≡ , ( x ; q)β (xj ; qj )βj n

(10.2)

j =1

T. Ernst, A Comprehensive Treatment of q-Calculus, DOI 10.1007/978-3-0348-0431-8_10, © Springer Basel 2012

359

360

10

 q ! ≡ {l}

n 

q-functions of several variables

{lj }qj !,

(10.3)

j =1 n 

{ α }m,  q ≡

{αj }mj ,qj ,

(10.4)

j =1 k

q (2) ≡

n 

kj

qj ( 2 ) ,

(10.5)

j =1 

(−1)k ≡ (−1)|k| ,

 ≡

n 

j ,

(10.6)

j =1 n 

Pk, x , y) ≡  q (

Pkj ,qj (xj , yj ),

(10.7)

j =1

 α ; qk ≡

n 

αj ; qj kj .

(10.8)

j =1

The q-factorial (10.8) is usually written (α); q k . The partial q-derivative of a function of n variables is defined as an operator in the spirit of Hörmander [285, p. 12]: n  

 l Dqjj ,xj F ( x , q),



x , q) ≡ Dlq,x F (

(10.9)

j =1

n  l  t l Dq,x t F ( Dqj ,xj jj j F ( x , q) ≡ x , q ).



(10.10)

j =1

Closed and open intervals are defined by  ≡ [ a , b]

n 

[aj , bj ],

 ≡ ( a , b)

j =1

n 

(aj , bj ).

(10.11)

j =1

Jackson [299, p. 145], [300], [304, p. 146] has shown certain connections be ak x f (k) tween power series in x and series of the form ∞ k=0 (x;q)k , where f (k) is an integer-valued function. In 1921 Ryde [444] showed that certain linear homogeneous q-difference equations have series ∞  ak k=0

as solutions.

(x; q −1 )k

10.1

The corresponding vector notation

361

We need a q-analogue of holomorphic functions, which will be useful to characterize the functions to the far right in operator expressions.  q,n denote the class of functions F ( Definition 163 Let H x ) of n variables which can be written in the form F ( x) ≡

 ∞   0 k=

xαk

γk δk

 ( x q ; q ±1 )β

,

k

where α k ∈ N , βk ∈ Rn , γk ∈ Cn , δk ∈ Nn . n

(10.12)

 q,n (O). If the function is defined in an open region O