Function: lambertw
Section: transcendental
C-Name: glambertW
Prototype: Gp
Help: lambertw(y): solution of the implicit equation x*exp(x)=y.
Doc: Lambert $W$ function, solution of the implicit equation $xe^x=y$,
 for a positive real number $y$. This is the restriction to the positive
 reals of the complex principal branch $W_0$, which is not implemented
 outside of $\R^*_+$. Other branches $W_k$ for $k\neq 0$ are not implemented
 either.
