In q-analog theory, the -gamma function, or basic gamma function, is a generalization of the ordinary gamma function closely related to the double gamma function. It was introduced by Jackson (1905). It is given by
when , and
if . Here is the infinite q-Pochhammer symbol. The -gamma function satisfies the functional equation
In addition, the -gamma function satisfies the q-analog of the Bohr–Mollerup theorem, which was found by Richard Askey (Askey (1978)).
For non-negative integers n,
where is the q-factorial function. Thus the -gamma function can be considered as an extension of the q-factorial function to the real numbers.
The relation to the ordinary gamma function is made explicit in the limit
There is a simple proof of this limit by Gosper. See the appendix of (Andrews ( 1986 )).
The -gamma function satisfies the q-analog of the Gauss multiplication formula (Gasper & Rahman (2004)):
The -gamma function has the following integral representation (Ismail ( 1981 )):
Moak obtained the following q-analogue of the Stirling formula (see Moak (1984)):
where , denotes the Heaviside step function, stands for the Bernoulli number, is the dilogarithm, and is a polynomial of degree satisfying
Due to I. Mező, the q-analogue of the Raabe formula exists, at least if we use the q-gamma function when . With this restriction
El Bachraoui considered the case and proved that
The following special values are known. [1]
These are the analogues of the classical formula .
Moreover, the following analogues of the familiar identity hold true:
Let be a complex square matrix and Positive-definite matrix. Then a q-gamma matrix function can be defined by q-integral: [2]
where is the q-exponential function.
For other q-gamma functions, see Yamasaki 2006. [3]
An iterative algorithm to compute the q-gamma function was proposed by Gabutti and Allasia. [4]
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