\begin{equation}
\label{log likelihood}
    \log p(Y)\ge \mathcal{L} (\boldsymbol{\theta })=\mathbb{E} _{q(\boldsymbol{x(0)},\boldsymbol{f},U)}\left[ \log \frac{p(\boldsymbol{f},U,\boldsymbol{x}(0),Y)}{q(\boldsymbol{x}(0),\boldsymbol{f},U)} \right] 
\end{equation}
