\begin{equation}
  \frac{\mathcal{Z}_+}{\mathcal{Z}_-}=\exp\left[\frac{2X_\alpha^{(\ell+1)\mu} W^{(\ell)T}_\alpha X^{(\ell)\mu}}{\Delta^{(\ell+1)}_X+\Delta^{(\ell+1)}_Z}\right] \frac{1+\text{erf}(q_+)}{\text{erfc}(q_-)} 
\end{equation}
