\end{center}
-Given a training set $x_1, \dots, x_N$ that follows an unknown
-distribution $\mu_X$, we want to fit a model $p_\theta(x,z)$ to it,
-maximizing
+Given a training i.i.d train samples $x_1, \dots, x_N$ that follows an
+unknown distribution $\mu_X$, we want to fit a model $p_\theta(x,z)$
+to it, maximizing
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\[
\sum_n \log \, p_\theta(x_n).
\]
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-If we do not have a analytical form of the marginal $p_\theta(x_n)$
+If we do not have an analytical form of the marginal $p_\theta(x_n)$
but only the expression of $p_\theta(x_n,z)$, we can get an estimate
of the marginal by sampling $z$ with any distribution $q$
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