Function: intmellininvshort
Section: sums
C-Name: intmellininvshort
Prototype: GGGp
Help: intmellininvshort(sig,x,tab): numerical integration on the 
 line real(z) = sig (or sig[1]) of s(z)x^(-z)dz/(2*I*Pi), i.e. inverse Mellin
 transform of s at x. sig is coded as follows: either it is real, and then
 by default assume s(z) decreases like exp(-z). Or sig = [sigR, al], sigR is
 the abcissa of integration, and al = 0 for slowly decreasing functions, or
 al > 0 if s(z) decreases like exp(-al*z). Compulsory table tab has been 
 precomputed using the command intfuncinit(t=[[-1],sig[2]],[[1],sig[2]],s) 
 (with possibly its two optional additional parameters), where sig[2] = 1
 if not given. Orders of magnitude faster than intmellininv.

