# 자코비 타원함수

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## 개요

$$\text{sn}(z|-1)=z-\frac{z^5}{10}+\frac{z^9}{120}-\frac{11 z^{13}}{15600}+\frac{211 z^{17}}{3536000}+O\left(z^{21}\right)$$

## 덧셈공식

\begin{align}\operatorname{cn}(x+y) & ={\operatorname{cn}(x)\;\operatorname{cn}(y)- \operatorname{sn}(x)\;\operatorname{sn}(y)\;\operatorname{dn}(x)\;\operatorname{dn}(y)\over {1 - k^2 \;\operatorname{sn}^2 (x) \;\operatorname{sn}^2 (y)}}, \\[8pt]\operatorname{sn}(x+y) & ={\operatorname{sn}(x)\;\operatorname{cn}(y)\;\operatorname{dn}(y) +\operatorname{sn}(y)\;\operatorname{cn}(x)\;\operatorname{dn}(x)\over {1 - k^2 \;\operatorname{sn}^2 (x)\; \operatorname{sn}^2 (y)}}, \\[8pt]\operatorname{dn}(x+y) & ={\operatorname{dn}(x)\;\operatorname{dn}(y)- k^2 \;\operatorname{sn}(x)\;\operatorname{sn}(y)\;\operatorname{cn}(x)\;\operatorname{cn}(y)\over {1 - k^2 \;\operatorname{sn}^2 (x)\; \operatorname{sn}^2 (y)}}.\end{align}

## 관련논문

• Kiselev, Oleg. “Uniform Asymptotic Behaviour of Jacobi-$\operatorname{sn}$ near a Singular Point. The Lost Formula from Handbooks for Elliptic Functions.” arXiv:1510.06602 [nlin], October 22, 2015. http://arxiv.org/abs/1510.06602