Product of elliptic Weierstrass function, shifted by half-periods

82 Views Asked by At

For those who have the book, this is from McKean and Moll's book on elliptic curves, exercise 2.14.7. This section deals with the Weierstrass elliptic function with periods $\omega_1$ and $\omega_2$, and this section operates under the assumption that $e_1+e_2+e_3=0$.

I was able to show in exercise 6 that $\wp(x+\omega_1/2)=e_1+(e_1-e_2)(e_1-e_3)[\wp(x)-e_1]^{-1}$, and that similar inequalities hold for the other two half-periods $(\omega_1+\omega_2)/2$ and $\omega_2/2$. Now if we add the three results together, along with $\wp(x)$, we get $4\wp(2x)$ from exercise 5, and this is fine. Exercise 7 then asks ``for the corresponding product'', which I can only assume is $$\wp(x)\wp\left(x+\frac{\omega_1}{2}\right)\wp\left(x+\frac{\omega_1+\omega_2}{2}\right)\wp\left(x+\frac{\omega_2}{2}\right).$$ Note that this product has a pole of order two at $x=0$, and this pole only appears in the first factor of this product. However the exercise is claiming that the answer is $$[\wp'(x)]^2\cdot 16(e_1-e_2)^2(e_2-e_3)^2(e_3-e_1)^2,$$ which has a pole of order six at $x=0$. I take it that this pole order discrepancy implies that the two elliptic functions cannot be equal (or perhaps I have a fundamental misunderstanding of complex analysis?), implying that the book has yet another typo. Am I mistaken in my thought process? Or have people resolved this issue before?