\begin{equation}\label{eq:GRU}
\begin{aligned}
z_t &= \sigma(W_z x_t + U_z h_{t-1} + b_z), \\
r_t &= \sigma(W_r x_t + U_r h_{t-1} + b_r), \\
\tilde{h}_t &= \tanh(W_h x_t + U_h (r_t \odot h_{t-1}) + b_h), \\
h_t &= (1 - z_t) \odot h_{t-1} + z_t \odot \tilde{h}_t,
\end{aligned}
\end{equation}
