Function: zetahurwitz
Section: transcendental
C-Name: zetahurwitz
Prototype: GGp
Help: zetahurwitz(s,x): Hurwitz zeta function at s, x. s must be of real
 part > 1 and x must be a positive real number.
Doc: Hurwitz zeta function $\zeta(s,x)=\sum_{n\ge0}(n+x)^{-s}$. We must have
 $\Re(s)>1$ and $x$ real positive. Note that $\zeta(s,1) = \zeta(s)$
 \bprog
 ? zetahurwitz(Pi,Pi)
 %1 = 0.056155444497585099925180502385781494486
 ? zetahurwitz(2,1) - zeta(2)
 %2 = -2.350988701644575016 E-38
 @eprog\noindent We also define $\zeta(1,x) = - \psi(x)$, where $\psi$
 is the digamma function (\kbd{psi}).
 \bprog
 ? zetahurwitz(1,1) - Euler
 %3 = 2.644862289350146893 E-38
 @eprog
