The Student Room Group

Weierstrass psi function limit

1. The problem statement, all variables and given/known data

Show that limz0z2(ψ(z)ψ(wj2))=1\lim_{z \to 0} z^2( \psi(z)-\psi(\frac{w_j}{2})) =1

where ψ(z)=1z2+wΩ1(zw)21w2\psi(z)=\frac{1}{z^2}+\sum\limits_{w \in \Omega}' \frac{1}{(z-w)^2}-\frac{1}{w^2}

where Ω\Omega are the periods of ψ(z)\psi(z)

2. The attempt at a solution

limz0z2(ψ(z)ψ(wj2))=1+wΩz2(zw)2z2w2\lim_{z \to 0} z^2( \psi(z)-\psi(\frac{w_j}{2}))= 1 + \sum\limits_{w\in \Omega}'\frac{z^2}{(z-w)^2}-\frac{z^2}{w^2}
The last time clearly vanishes.

For the second term I can write this as 1(1wz)21\frac{1}{(1-\frac{w}{z})^2} \to 1 as z0z \to 0 So I get limz0z2(ψ(z)ψ(wj2))=1+wΩ1\lim_{z \to 0} z^2( \psi(z)-\psi(\frac{w_j}{2})) =1+ \sum_{w \in \Omega}' 1

MY QUESTION

I don't really understand the summation second term here. n=1n=n1=n\sum_{n=1}^{n=n} 1 = n right?

So there's an infinite number of wΩ w \in \Omega so obviously I dont want to do this, are you in affect looking at the limit 'modΩmod \Omega ', so where the first term corresponds to w=0w=0 , i.e so that's us done, the limit taken for mod \Omega ?

Many thanks

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