\[\sigma\left(z\right)=\frac{2\omega_{1}}{\pi}\exp\left(\frac{\eta_{1}z^{2}}{2%
\omega_{1}}\right)\sin\left(\frac{\pi z}{2\omega_{1}}\right)\*\prod_{n=1}^{%
\infty}\frac{1-2q^{2n}\cos\left(\pi z/\omega_{1}\right)+q^{4n}}{(1-q^{2n})^{2}},\]