Function: psi
Section: transcendental
C-Name: gpsi_der
Prototype: GD0,L,p
Help: psi(x,{der}): psi-function at x (der-th derivative of psi if der is set)
Doc: the $\psi$-function of $x$, i.e.~the logarithmic derivative
 $\Gamma'(x)/\Gamma(x)$. If $\var{der}$ is set, return the $\var{der}$-th derivative.
 For $s$ a \typ{PADIC}, evaluates the $\var{der}$-th derivative of the Morita
 $\psi$ function at $s$.
Variant: For a \typ{PADIC} $x$, the function
 \fun{GEN}{Qp_psi}{GEN x, long der} is also available.
 For $\var{der} = 0$,
 \fun{GEN}{gpsi}{GEN x, long prec} is also available.
