Function: pollaguerre
Section: polynomials
C-Name: pollaguerre_eval0
Prototype: LDGDGD0,L,
Help: pollaguerre(n,{a=0},{b='x},{flag=0}): Laguerre polynomial of degree n
 and parameter a evaluated at b. If flag is 1, return [L^{(a)_{n-1}(b),
 L^{(a)}_n(b)].
Doc: $n^{\text{th}}$ \idx{Laguerre polynomial} $L^{(a)}_{n}$ of degree $n$ and
 parameter $a$ evaluated at $b$ (\kbd{'x} by default), i.e.
 $$ L_{n}^{(a)}(x) =
    \dfrac{x^{-a}e^{x}}{n!} \dfrac{d^{n}}{dx^{n}}\big(e^{-x}x^{n+a}\big).$$
 If \fl\ is $1$, return $[L^{(a)}_{n-1}(b), L_{n}^{(a)}(b)]$.
Variant: To obtain the $n$-th Laguerre polynomial in variable $v$,
 use \fun{GEN}{pollaguerre}{long n, GEN a, GEN b, long v}. To obtain
 $L^{(a)}_{n}(b)$, use \fun{GEN}{pollaguerre_eval}{long n, GEN a, GEN b}.
