[main.tex] Motivate exact resolution of l0 problems.

main.tex

@@ -586,6 +586,20 @@
 	\end{columns}	
 \end{frame}
 
+\begin{frame}
+	\frametitle{Exact resolution}
+	\begin{equation*}
+		\min_{\xb \in \mathbb{R}^Q} \underbrace{\highlight{pink}{\tfrac{1}{2} {\|\yb - \Av \xb\|}_2^2}}_{\text{data fidelity}} + \underbrace{\highlight{lime}{\mu {\|\xb\|}_0}}_{\text{regularizer}}
+	\end{equation*} $\rightarrow$ NP-hard: combinatorial search.
+
+	Heuristics and relaxations:
+	\begin{itemize}
+		\item are exact if some conditions are met\footnote{\cite{Candes06_RIP}}\footnote{\cite{Tropp04_Greed_is_Good}},
+		\item provide sub-optimal solutions otherwise\footnote{\cite{Bertsimas_2016_BestSubset_Selection}}\footnote{\cite{Bourguignon_MIP_2016}}.
+	\end{itemize}
+
+\end{frame}
+
 \begin{frame}
 	\frametitle{Exact resolution}
 	\begin{equation*}