Paper 3, Section II, H

Riemann Surfaces | Part II, 2016

Let ff be a non-constant elliptic function with respect to a lattice Λ⊂C\Lambda \subset \mathbb{C}. Let P⊂CP \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 )

12πi∫∂Pzf′(z)f(z)dz\frac{1}{2 \pi i} \int_{\partial P} z \frac{f^{\prime}(z)}{f(z)} d z

show that

∑j=1naj−∑j=1nbj∈Λ\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,w∉Λv, 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 z∉Λ,z−v∉Λz \notin \Lambda, z-v \notin \Lambda and z−w∉Λz-w \notin \Lambda. Prove that f(z)=0f(z)=0 if and only if z+v+w∈Λz+v+w \in \Lambda. [You may use standard properties of the Weierstrass ℘\wp-function provided they are clearly stated.]

Typos? Please submit corrections to this page on GitHub.