Function: ellpointtoz
Section: elliptic_curves
C-Name: zell
Prototype: GGp
Help: ellpointtoz(E,P): lattice point z corresponding to the point P on the
 elliptic curve E.
Doc:
 if $E$ is an elliptic curve with coefficients
 in $\R$, this computes a complex number $t$ (modulo the lattice defining
 $E$) corresponding to the point $z$, i.e.~such that, in the standard
 Weierstrass model, $\wp(t)=z[1],\wp'(t)=z[2]$. In other words, this is the
 inverse function of \kbd{ellztopoint}. More precisely, if $(w1,w2)$ are the
 real and complex periods of $E$, $t$ is such that $0 \leq \Re(t) < w1$
 and $0 \leq \Im(t) < \Im(w2)$.

 If $E$ has coefficients in $\Q_p$, then either Tate's $u$ is in $\Q_p$, in
 which case the output is a $p$-adic number $t$ corresponding to the point $z$
 under the Tate parametrization, or only its square is, in which case the
 output is $t+1/t$. $E$ must be an \var{ell} as output by \kbd{ellinit}.
