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16 Generalized Hypergeometric Functions and Meijer G-FunctionMeijer G-Function

§16.17 Definition

Again assume a_{1},a_{2},\dots,a_{p} and b_{1},b_{2},\dots,b_{q} are real or complex parameters. Assume also that m and n are integers such that 0\leq m\leq q and 0\leq n\leq p, and none of a_{k}-b_{j} is a positive integer when 1\leq k\leq n and 1\leq j\leq m. Then the Meijer G-function is defined via the Mellin–Barnes integral representation:

where the integration path L separates the poles of the factors \mathop{\Gamma\/}\nolimits\!\left(b_{{\ell}}-s\right) from those of the factors \mathop{\Gamma\/}\nolimits\!\left(1-a_{{\ell}}+s\right). There are three possible choices for L, illustrated in Figure 16.17.1 in the case m=1, n=2:

  1. (i)

    L goes from -i\infty to i\infty. The integral converges if p+q<2(m+n) and |\mathop{\mathrm{ph}\/}\nolimits z|<(m+n-\frac{1}{2}(p+q))\pi.

  2. (ii)

    L is a loop that starts at infinity on a line parallel to the positive real axis, encircles the poles of the \mathop{\Gamma\/}\nolimits\!\left(b_{\ell}-s\right) once in the negative sense and returns to infinity on another line parallel to the positive real axis. The integral converges for all z (\neq 0) if p<q, and for 0<|z|<1 if p=q\geq 1.

  3. (iii)

    L is a loop that starts at infinity on a line parallel to the negative real axis, encircles the poles of the \mathop{\Gamma\/}\nolimits\!\left(1-a_{\ell}+s\right) once in the positive sense and returns to infinity on another line parallel to the negative real axis. The integral converges for all z if p>q, and for |z|>1 if p=q\geq 1.

See accompanying text See accompanying text See accompanying text
Case (i) Case (ii) Case (iii)
Figure 16.17.1: s-plane. Path L for the integral representation (16.17.1) of the Meijer G-function. Magnify

When more than one of Cases (i), (ii), and (iii) is applicable the same value is obtained for the Meijer G-function.

Assume p\leq q, no two of the bottom parameters b_{j}, j=1,\dots,m, differ by an integer, and a_{j}-b_{k} is not a positive integer when j=1,2,\dots,n and k=1,2,\dots,m. Then

where * indicates that the entry 1+b_{k}-b_{k} is omitted. Also,