Function: gammamellininv
Section: transcendental
C-Name: gammamellininv
Prototype: GGD0,L,b
Help: gammamellininv(G,t,{m=0}): returns G(t), where G is as output
 by gammamellininvinit (its m-th derivative if m is present).
Doc: returns the value at $t$ of the inverse Mellin transform
 $G$ initialized by \tet{gammamellininvinit}. If the optional parameter
 $m$ is present, return the $m$-th derivative $G^{(m)}(t)$.

 \bprog
 ? G = gammamellininvinit([0]);
 ? gammamellininv(G, 2) - 2*exp(-Pi*2^2)
 %2 = -4.484155085839414627 E-44
 @eprog

 The shortcut
 \bprog
   gammamellininv(A,t,m)
 @eprog\noindent for
 \bprog
   gammamellininv(gammamellininvinit(A,m), t)
 @eprog\noindent is available.
