Evidence lower bound (source code)

= Evidence lower bound
{title2=$\operatorname{ELBO}$}
{wiki}

For posterior proportional to $L(\theta)\pi(\theta)$ and approximation $q$,
$$
\operatorname{ELBO}(q)=\mathbb E_q\log L(\theta)-D_{\mathrm{KL}}(q\Vert\pi),
$$
and $\log Z=\operatorname{ELBO}(q)+D_{\mathrm{KL}}(q\Vert p(\theta\mid y))$.