Paper 3, Section II, H

Riemann Surfaces
Part II, 2016

Let ff be a non-constant elliptic function with respect to a lattice ΛC\Lambda \subset \mathbb{C}. Let PCP \subset \mathbb{C} be a fundamental parallelogram and let the degree of ff be nn. Let a1,,ana_{1}, \ldots, a_{n} denote the zeros of ff in PP, and let b1,,bnb_{1}, \ldots, b_{n} denote the poles (both with possible repeats). By considering the integral (if required, also slightly perturbing PP )

12πiPzf(z)f(z)dz\frac{1}{2 \pi i} \int_{\partial P} z \frac{f^{\prime}(z)}{f(z)} d z

show that

j=1najj=1nbjΛ\sum_{j=1}^{n} a_{j}-\sum_{j=1}^{n} b_{j} \in \Lambda

Let (z)\wp(z) denote the Weierstrass \wp-function with respect to Λ\Lambda. For v,wΛv, w \notin \Lambda with (v)(w)\wp(v) \neq \wp(w) we set

f(z)=det(111(z)(v)(w)(z)(v)(w))f(z)=\operatorname{det}\left(\begin{array}{ccc} 1 & 1 & 1 \\ \wp(z) & \wp(v) & \wp(w) \\ \wp^{\prime}(z) & \wp^{\prime}(v) & \wp^{\prime}(w) \end{array}\right)

an elliptic function with periods Λ\Lambda. Suppose zΛ,zvΛz \notin \Lambda, z-v \notin \Lambda and zwΛz-w \notin \Lambda. Prove that f(z)=0f(z)=0 if and only if z+v+wΛz+v+w \in \Lambda. [You may use standard properties of the Weierstrass \wp-function provided they are clearly stated.]