Restructured presentation

This commit is contained in:
Andreas Tsouchlos 2023-04-18 17:04:55 +02:00
parent d49cdd4394
commit 6bf75ae5bd
5 changed files with 2854 additions and 2883 deletions

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@ -288,12 +288,17 @@
\setnextsection{0}
\input{sections/theoretical_background.tex}
\input{sections/decoding_algorithms.tex}
\input{sections/examination_results.tex}
%\input{sections/forthcoming_examination.tex}
\input{sections/proximal_decoding.tex}
\input{sections/lp_dec_using_admm.tex}
\input{sections/comparison.tex}
\input{sections/question_slide.tex}
% \input{sections/decoding_algorithms.tex}
% \input{sections/examination_results.tex}
%\input{sections/forthcoming_examination.tex}
% \input{sections/comparison.tex}
\begin{frame}[allowframebreaks]
\frametitle{Bibliography}
\printbibliography[heading=none]

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@ -1,958 +1 @@
\section{Decoding Algorithms}%
\label{sec:Decoding Algorithms}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{Proximal Decoding}%
\label{sub:Alg Proximal Decoding}
\begin{frame}[t]
\frametitle{Proximal Decoding: General Idea \cite{proximal_paper}}
\vspace*{-0.3cm}
\begin{itemize}
\item MAP rule as continuous maximization problem:
\begin{align*}
\hat{\boldsymbol{x}}
&= \argmax_{\tilde{\boldsymbol{x}}\in\mathbb{R}^n}
f_{\boldsymbol{Y}}\left( \boldsymbol{y} | \tilde{\boldsymbol{x}} \right)
f_{\boldsymbol{X}}\left( \tilde{\boldsymbol{x}} \right)\\
&= \argmax_{\tilde{\boldsymbol{x}}\in\mathbb{R}^n}
e^{-L\left( \boldsymbol{y} | \tilde{\boldsymbol{x}}\right)}
f_{\boldsymbol{X}}\left( \tilde{\boldsymbol{x}} \right),
\hspace{5mm} L\left( \boldsymbol{y} | \tilde{\boldsymbol{x}} \right)
= - \ln\left( f_{\boldsymbol{Y}}
\left( \boldsymbol{y} | \tilde{\boldsymbol{x}} \right) \right)
\end{align*}
\item Approximation of prior PDF:
\begin{align*}
f_{\boldsymbol{X}}\left( \tilde{\boldsymbol{x}} \right)
= \frac{1}{\left| \mathcal{C} \right| }
\sum_{\boldsymbol{c} \in \mathcal{C} }
\delta\left( \tilde{\boldsymbol{x}} - \left( -1 \right)^{\boldsymbol{c}}
\right)
\approx \frac{1}{Z} e^{-\gamma h\left( \tilde{\boldsymbol{x}} \right) }
\end{align*}
\item Code constraint polynomial:
\begin{minipage}[c]{0.56\textwidth}
\raggedright
\begin{align*}
h\left( \tilde{\boldsymbol{x}} \right) =
\underbrace{\sum_{i=1}^{n} \left( \tilde{x}_i^2 - 1 \right)^2}_{\text{Bipolar
constraint}}
+ \underbrace{\sum_{j=1}^{m} \left[ \left(
\prod_{i\in N_v\left( j \right)} \tilde{x}_i\right) -1 \right]^2}
_{\text{Parity constraint}},
\end{align*}
\end{minipage}%
\begin{minipage}[c]{0.4\textwidth}
\raggedleft
\begin{flalign*}
\mathcal{I} &:= \left[1\text{ : }n\right],
\hspace{2mm} \mathcal{J} := \left[1\text{ : }m\right] \\
N_v\left( j \right) &:= \left\{i | i\in \mathcal{I},
\boldsymbol{H}_{j,i} = 1
\right\}, j\in\mathcal{J}\\
\end{flalign*}
\end{minipage}
\hfill
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{Proximal Decoding: General Idea}
\begin{itemize}
\item Objective function:
\begin{align*}
g\left( \tilde{\boldsymbol{x}} \right)
= L\left( \boldsymbol{y} | \tilde{\boldsymbol{x}} \right)
+ \gamma h\left( \tilde{\boldsymbol{x}} \right)
\end{align*}
\note{Notational difference between $f$ and $f_X$ or $f_Y$}
\item Proximal operator \cite{proximal_algorithms}:
\begin{align*}
\text{prox}_{\gamma h} \left( \tilde{\boldsymbol{x}} \right) &\equiv
\argmin_{\boldsymbol{t}\in\mathbb{R}^n}
\gamma h\left( \boldsymbol{t} \right) + \frac{1}{2} \lVert \boldsymbol{t}
- \tilde{\boldsymbol{x}} \rVert^2 \\
&\approx \tilde{\boldsymbol{x}}
- \gamma \nabla h\left( \tilde{\boldsymbol{x}} \right),
\hspace{5mm} \gamma \text{ small}
\end{align*}
\item Iterative decoding process:
\begin{align*}
\boldsymbol{r} &\leftarrow \boldsymbol{s}
- \omega \nabla L\left( \boldsymbol{y} | \boldsymbol{s}
\right), \hspace{5mm} \omega > 0
\hspace{10mm} \text{``Gradient descent step''}\\
\boldsymbol{s} &\leftarrow \boldsymbol{r}
- \gamma \nabla h\left( \boldsymbol{r}
\right), \hspace{9mm} \gamma > 0
\hspace{10mm} \text{``Code proximal step''}
\end{align*}
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t, fragile]
\frametitle{Proximal Decoding: Algorithm}
\begin{itemize}
\item Iterative decoding algorithm \cite{proximal_paper}:
\end{itemize}
\vspace{2mm}
\begin{algorithm}[caption={}, label={}]
$\boldsymbol{s} \leftarrow \boldsymbol{0}$
for $K$ iterations do
$\boldsymbol{r} \leftarrow \boldsymbol{s} - \omega \nabla L \left( \boldsymbol{y} \mid \boldsymbol{s} \right) $
$\boldsymbol{s} \leftarrow \boldsymbol{r} - \gamma \nabla h\left( \boldsymbol{r} \right) $
$\boldsymbol{\hat{x}} \leftarrow \text{sign}\left( \boldsymbol{s} \right) $
if $\boldsymbol{H}\boldsymbol{\hat{c}} = \boldsymbol{0}$ do
return $\boldsymbol{\hat{c}}$
end if
end for
return $\boldsymbol{\hat{c}}$
\end{algorithm}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\subsection{LP Decoding using ADMM}%
\label{sub:LP Decoding using ADMM}
\begin{frame}[t]
\frametitle{LP Decoding \cite{feldman_paper}}
\begin{itemize}
\item General reformulation of ML decoding as a linear program (LP)
% \item Codeword polytope:
% \begin{align*}
% \text{poly}\left( \mathcal{C} \right) =
% \left\{
% \sum_{\boldsymbol{c}\in\mathcal{C}}\alpha_{\boldsymbol{c}}
% \boldsymbol{c} : \alpha_{\boldsymbol{c}} \ge 0,
% \sum_{\boldsymbol{c}\in\mathcal{C}}\alpha_{\boldsymbol{c}} = 1
% \right\},
% \hspace{5mm} \alpha_{\boldsymbol{c}} \in \mathbb{R}_{\ge 0}
% \end{align*}
\item Cost function:
\begin{align*}
\boldsymbol{\gamma}^{T} \boldsymbol{c} = \sum_{i=1}^{n}
\gamma_i c_i,
\hspace{5mm}\gamma_i = \ln\left(
\frac{f_{Y_i \mid C_i}\left( y_i | c_i = 0 \right) }
{f_{Y_i \mid C_i}\left(y_i | c_i=1 \right) } \right)
\end{align*}
\item Exact \textit{integer linear programming} (ILP) formulation of ML decoding:
\begin{align*}
&\text{minimize } \boldsymbol{\gamma}^\text{T} \boldsymbol{c}\\
&\text{subject to } \boldsymbol{c}\in \mathcal{C}
\end{align*}
\item Goal: relaxation of constraints to make a practical solution to the problem feasible
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{LP Relaxation: Motivation}
\vspace*{-1cm}
\begin{gather*}
% \boldsymbol{G} =
% \begin{bmatrix}
% 0 & 1 & 1
% \end{bmatrix} \hspace{1cm}
\boldsymbol{H} =
\begin{bmatrix}
1 & 1 & 1\\
0 & 1 & 1
\end{bmatrix} \hspace{1cm}
% \\[1em]
\mathcal{C} = \left\{ \begin{bmatrix} 0 \\ 0 \\ 0 \end{bmatrix},
\begin{bmatrix} 0 \\ 1 \\ 1 \end{bmatrix} \right\}
\end{gather*}%
\vspace*{-5mm}
\begin{figure}[H]
\centering
\begin{subfigure}[c]{0.4\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.9, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\end{tikzpicture}
\caption{Set of all codewords $\mathcal{C}$}
\label{fig:lp:poly:exact_ilp}
\end{subfigure}%
\begin{subfigure}[c]{0.16\textwidth}
\centering
\begin{tikzpicture}
\node (relaxation) at (0, 0) {Relaxation};
\draw (-1.5, 0) -- (relaxation);
\draw[->] (relaxation) -- (1.5, 0);
\end{tikzpicture}
\end{subfigure}%
\begin{subfigure}[c]{0.4\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.9, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
% Polytope Edges
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\end{tikzpicture}
\caption{Codeword polytope $\text{poly}\left( \mathcal{C} \right) $}
\label{fig:lp:poly:exact}
\end{subfigure}
\end{figure}
% \vspace*{-5mm}
\begin{align*}
\text{poly}\left( \mathcal{C} \right) =
\left\{
\sum_{\boldsymbol{c}\in\mathcal{C}}\alpha_{\boldsymbol{c}}
\boldsymbol{c} : \alpha_{\boldsymbol{c}} \ge 0,
\sum_{\boldsymbol{c}\in\mathcal{C}}\alpha_{\boldsymbol{c}} = 1
\right\},
\hspace{5mm} \alpha_{\boldsymbol{c}} \in \mathbb{R}_{\ge 0}
\end{align*}
\end{frame}
\begin{frame}[t]
\frametitle{LP Relaxation}
\vspace*{-1cm}
\begin{figure}[H]
\centering
\begin{subfigure}[c]{0.48\textwidth}
\centering
\begin{minipage}{\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.7, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c101) at (p101) {};
\node[codeword] (c110) at (p110) {};
\node[codeword] (c011) at (p011) {};
% Polytope Edges & Faces
\draw[line width=1pt, color=KITblue] (c000) -- (c101);
\draw[line width=1pt, color=KITblue] (c000) -- (c110);
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
\draw[line width=1pt, color=KITblue] (c101) -- (c110);
\draw[line width=1pt, color=KITblue] (c101) -- (c011);
\draw[line width=1pt, color=KITblue] (c011) -- (c110);
\fill[KITblue, opacity=0.15] (p000) -- (p101) -- (p011) -- cycle;
\fill[KITblue, opacity=0.15] (p000) -- (p110) -- (p101) -- cycle;
\fill[KITblue, opacity=0.15] (p110) -- (p011) -- (p101) -- cycle;
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, right=0.07cm of c101] {$\left( 1, 0, 1 \right) $};
\node[color=KITblue, right=0cm of c110] {$\left( 1, 1, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\node[color=KITblue, align=center] at (-4,1)
{$j=1$\\ $\left( c_1 + c_2+ c_3 = 0 \right) $};
\end{tikzpicture}
\end{minipage}
\vspace{5mm}
\begin{minipage}{\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.7, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
\node[codeword] (c100) at (p100) {};
\node[codeword] (c111) at (p111) {};
% Polytope Edges & Faces
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
\draw[line width=1pt, color=KITblue] (c000) -- (c100);
\draw[line width=1pt, color=KITblue] (c100) -- (c111);
\draw[line width=1pt, color=KITblue] (c111) -- (c011);
\fill[KITblue, opacity=0.2] (p000) -- (p100) -- (p111) -- (p011) -- cycle;
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\node[color=KITblue, below=0cm of c100] {$\left( 1, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c111] {$\left( 1, 1, 1 \right) $};
\node[color=KITblue, align=center] at (-4,1)
{$j=2$\\ $\left(c_2 + c_3 = 0\right)$};
\end{tikzpicture}
\end{minipage}
\caption{Local codeword polytopes $\mathcal{P}_{d_j}$ of the check nodes}
\label{fig:lp:poly:local}
\end{subfigure}%
\begin{subfigure}[c]{0.18\textwidth}
\centering
\begin{tikzpicture}
\draw[densely dashed] (0, -2) -- (0, 2);
\draw[densely dashed] (-0.5, -2) -- (0, -2);
\draw[densely dashed] (-0.5, 2) -- (0, 2);
\node (intersection) at (1.5, 0) {Intersection};
\draw[densely dashed] (0, 0) -- (intersection);
\draw[densely dashed, ->] (intersection) -- (3,0);
\end{tikzpicture}
\end{subfigure}%
\begin{subfigure}[c]{0.32\textwidth}
\centering
\vspace*{1.5cm}
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tikzstyle{pseudocodeword} = [color=KITred, fill=KITred,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.9, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
\node[pseudocodeword] (cpseudo) at (2, 1, 1) {};
% Polytope Edges & Faces
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
\draw[line width=1pt, color=KITred] (cpseudo) -- (c000);
\draw[line width=1pt, color=KITred] (cpseudo) -- (c011);
\fill[KITred, opacity=0.2] (p000) -- (p011) -- (2,1,1) -- cycle;
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\node[color=KITred, right=0cm of cpseudo]
{$\left( 1, \frac{1}{2}, \frac{1}{2} \right) $};
\end{tikzpicture}
\vspace*{-5mm}
\begin{gather*}
\boldsymbol{T}_j\tilde{\boldsymbol{c}} \in \mathcal{P}_{d_j}, \hspace{2mm}
\forall j\in \mathcal{J} \\[0.5em]
\boldsymbol{T}_j \in \mathbb{F}_2^{d_j \times n}
\end{gather*}
\vspace*{-2mm}
\caption{Relaxed codeword polytope $\overline{Q}$}
\label{fig:lp:poly:relaxed}
\end{subfigure}
\end{figure}
\end{frame}
\begin{frame}[t]
\frametitle{LP Relaxation}
\vspace{-5mm}
\begin{figure}[H]
\centering
\begin{subfigure}[t]{0.3\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.8, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\end{tikzpicture}
\begin{align*}
\text{minimize}\hspace{2mm} &\boldsymbol{\gamma}^\text{T} \boldsymbol{c} \\
\text{subject to}\hspace{2mm} &\boldsymbol{c} \in \mathcal{C}
\end{align*}
\caption{\textit{Integer linear program} (ILP)}
\end{subfigure}%
\hfill%
\begin{subfigure}[t]{0.3\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.8, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
% Polytope Edges
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\end{tikzpicture}
\begin{align*}
\text{minimize}\hspace{2mm} &\boldsymbol{\gamma}^\text{T} \tilde{\boldsymbol{c}} \\
\text{subject to}\hspace{2mm} &\tilde{\boldsymbol{c}} \in
\text{poly}\left( \mathcal{C} \right) &\
\end{align*}
\caption{Motivation}
\end{subfigure}%
\hfill%
\begin{subfigure}[t]{0.3\textwidth}
\centering
\tikzstyle{codeword} = [color=KITblue, fill=KITblue,
draw, circle, inner sep=0pt, minimum size=4pt]
\tikzstyle{pseudocodeword} = [color=KITred, fill=KITred,
draw, circle, inner sep=0pt, minimum size=4pt]
\tdplotsetmaincoords{60}{25}
\begin{tikzpicture}[scale=0.8, tdplot_main_coords]
\tikzstyle{every node}=[font=\normalsize]
% Cube
\coordinate (p000) at (0, 0, 0);
\coordinate (p001) at (0, 0, 2);
\coordinate (p010) at (0, 2, 0);
\coordinate (p011) at (0, 2, 2);
\coordinate (p100) at (2, 0, 0);
\coordinate (p101) at (2, 0, 2);
\coordinate (p110) at (2, 2, 0);
\coordinate (p111) at (2, 2, 2);
\draw[] (p000) -- (p100);
\draw[] (p100) -- (p101);
\draw[] (p101) -- (p001);
\draw[] (p001) -- (p000);
\draw[dashed] (p010) -- (p110);
\draw[] (p110) -- (p111);
\draw[] (p111) -- (p011);
\draw[dashed] (p011) -- (p010);
\draw[dashed] (p000) -- (p010);
\draw[] (p100) -- (p110);
\draw[] (p101) -- (p111);
\draw[] (p001) -- (p011);
% Polytope Vertices
\node[codeword] (c000) at (p000) {};
\node[codeword] (c011) at (p011) {};
\node[pseudocodeword] (cpseudo) at (2, 1, 1) {};
% Polytope Edges & Faces
\draw[line width=1pt, color=KITblue] (c000) -- (c011);
\draw[line width=1pt, color=KITred] (cpseudo) -- (c000);
\draw[line width=1pt, color=KITred] (cpseudo) -- (c011);
\fill[KITred, opacity=0.2] (p000) -- (p011) -- (2,1,1) -- cycle;
% Polytope Annotations
\node[color=KITblue, below=0cm of c000] {$\left( 0, 0, 0 \right) $};
\node[color=KITblue, above=0cm of c011] {$\left( 0, 1, 1 \right) $};
\node[color=KITred, right=0cm of cpseudo]
{$\left( 1, \frac{1}{2}, \frac{1}{2} \right) $};
\end{tikzpicture}
\begin{align*}
\text{minimize}\hspace{2mm} &\boldsymbol{\gamma}^\text{T} \tilde{\boldsymbol{c}} \\
\text{subject to}\hspace{2mm} &
\boldsymbol{T}_j\tilde{\boldsymbol{c}} \in \mathcal{P}_{d_j}, \hspace{2mm}
\forall j\in \mathcal{J}
\end{align*}
\caption{\textit{Linear code linear program} (LCLP)}
\end{subfigure}%
\end{figure}
\vspace*{-5.75cm}
\begin{figure}[H]
\centering
\begin{subfigure}[t]{0.36\textwidth}
\centering
\begin{tikzpicture}
\node (relaxation) at (0, 0) {Relaxation};
\draw[->] (-1, -0.25) -- (1, -0.25);
% \draw (-1.5, 0) -- (relaxation);
% \draw[->] (relaxation) -- (1.5, 0);
\end{tikzpicture}
\end{subfigure}%
\begin{subfigure}[t]{0.31\textwidth}
\centering
\begin{tikzpicture}
\node (relaxation) at (0, 0) {Relaxation};
\draw[->] (-1, -0.25) -- (1, -0.25);
% \draw (-1.5, 0) -- (relaxation);
% \draw[->] (relaxation) -- (1.5, 0);
\end{tikzpicture}
\end{subfigure}%
\end{figure}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{LP Decoding using ADMM}
\begin{itemize}
\item Solution using the \textit{alternating direction method of multipliers} (ADMM)
\item Slight reformulation of the LCLP:
\begin{align*}
\begin{aligned}
\text{minimize}\hspace{2mm} &\boldsymbol{\gamma}^\text{T}\tilde{\boldsymbol{c}}
+ \sum_{j\in\mathcal{J}} g_j\left( \boldsymbol{z}_j \right) \\
\text{subject to}\hspace{2mm} &
\boldsymbol{T}_j\tilde{\boldsymbol{c}} = \boldsymbol{z}_j, \hspace{2mm}
\forall j\in \mathcal{J}
\end{aligned}\hspace{2mm},\hspace{1cm}
g_j\left( \boldsymbol{t} \right) := \begin{cases}
0, & \boldsymbol{t} \in \mathcal{P}_{d_j} \\
+\infty, & \boldsymbol{t} \not\in \mathcal{P}_{d_j}
\end{cases}
\end{align*}
\item Iterative algorithm:
\begin{alignat*}{3}
\tilde{\boldsymbol{c}} &\leftarrow \argmin_{\tilde{\boldsymbol{c}}}
\left( \boldsymbol{\gamma}^\text{T}\tilde{\boldsymbol{c}}
+ \frac{\mu}{2}\sum_{j\in\mathcal{J}} \left\Vert
\boldsymbol{T}_j\tilde{\boldsymbol{c}} - \boldsymbol{z}_j
+ \boldsymbol{u}_j \right\Vert \right) \\
\boldsymbol{z}_j &\leftarrow \argmin_{\boldsymbol{z}_j}
\left( g\left( \boldsymbol{z}_j \right)
+ \frac{\mu}{2} \left\Vert \boldsymbol{T}_j \tilde{\boldsymbol{c}}
- \boldsymbol{z}_j + \boldsymbol{u}_j \right\Vert \right),
\hspace{5mm} &&\forall j\in\mathcal{J} \\
\boldsymbol{u}_j &\leftarrow \boldsymbol{u}_j
+ \boldsymbol{T}_j\tilde{\boldsymbol{c}} - \boldsymbol{z}_j,
\hspace{5mm} &&\forall j\in\mathcal{J}
% \left( g\left( \boldsymbol{\boldsymbol{z}_j} \right)
% + \frac{\mu}{2} \left\Vert \boldsymbol{T}_j\tilde{\boldsymbol{c}}
% - \boldsymbol{z}_j + \boldsymbol{u}_j\right\Vert \right)
\end{alignat*}
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{frame}[t]
\frametitle{LP Decoding using ADMM}
\vspace*{-7mm}
\begin{itemize}
\item Convergence properties enhanced by over-relaxation with parameter $\rho$
\item Simplified rules%
\footnote{$\left( \boldsymbol{z}_j \right)_i $ is a slight abuse of notation.
What is actually meant is the component of $\boldsymbol{z}_j$ that is associated
with the VN $i$, i.e., $\left( \boldsymbol{T}_j^\text{T} \boldsymbol{z}_j \right)_i$.\\
The same is true for $\left( \boldsymbol{u}_j \right)_i$}%
:
\begin{alignat*}{3}
\tilde{c}_i &\leftarrow \frac{1}{\left| N_v\left( i \right) \right|} \left(
\sum_{j\in N_v\left( i \right) } \Big( \left( \boldsymbol{z}_j \right)_i
- \left( \boldsymbol{u}_j \right)_i \Big)
- \frac{\gamma_i}{\mu} \right)
\hspace{5mm} && \forall i\in\mathcal{I} \\
\boldsymbol{z}_j &\leftarrow \Pi_{\mathcal{P}_{d_j}}\left(
\boldsymbol{T}_j\tilde{\boldsymbol{c}} + \boldsymbol{u}_j \right)
\hspace{5mm} && \forall j\in\mathcal{J} \\
\boldsymbol{u}_j &\leftarrow \boldsymbol{u}_j
+ \boldsymbol{T}_j\tilde{\boldsymbol{c}}
- \boldsymbol{z}_j
\hspace{5mm} && \forall j\in\mathcal{J}
\end{alignat*}
\item The projections $\Pi_{\mathcal{P}_{d_j}}, \hspace{1mm} j\in\mathcal{J}$
are the main computational effort
\item Many approaches exist \cite{original_admm}, \cite{efficient_lp_dec_admm},
\cite{lautern}
\item The approach chosen here is the one described in \cite{original_admm}
\end{itemize}
\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\begin{frame}[t]
% \frametitle{LP Relaxation}
%
% \begin{minipage}[c]{0.6\linewidth}
% \begin{itemize}
% \item Set of all variable nodes incident to a check node:
% \begin{align*}
% N\left( j \right) \equiv \left\{
% i | i\in \mathcal{I},
% \boldsymbol{H}_{j,i} = 1
% \right\},
% j \in \mathcal{J}
% \end{align*}
% \begin{align*}
% S \subseteq N\left( j \right), \left| S \right| \text{odd}
% \end{align*}
% \item Relaxed polytope representation:
% \begin{align*}
% \sum_{i\in \left( N\left( j \right) \setminus S\right) } f_i
% + \sum_{i\in S} \left( 1 - f_i \right) \ge 1
% \end{align*}
% ``$\boldsymbol{f}$ is separated by at least one bitflip
% from all illegal configurations''
% \end{itemize}
% \end{minipage}%
% \hfill%
% \begin{minipage}[c]{0.4\linewidth}
% \begin{figure}[H]
% \centering
%
% \tikzstyle{codeword} = [color=KITblue, fill=KITblue,
% draw, circle, inner sep=0pt, minimum size=4pt]
%
% \tdplotsetmaincoords{60}{245}
% \begin{tikzpicture}[scale=1, transform shape, tdplot_main_coords]
% % Cube
%
% \draw[dashed] (0, 0, 0) -- (2, 0, 0);
% \draw[dashed] (2, 0, 0) -- (2, 0, 2);
% \draw[] (2, 0, 2) -- (0, 0, 2);
% \draw[] (0, 0, 2) -- (0, 0, 0);
%
% \draw[] (0, 2, 0) -- (2, 2, 0);
% \draw[] (2, 2, 0) -- (2, 2, 2);
% \draw[] (2, 2, 2) -- (0, 2, 2);
% \draw[] (0, 2, 2) -- (0, 2, 0);
%
% \draw[] (0, 0, 0) -- (0, 2, 0);
% \draw[dashed] (2, 0, 0) -- (2, 2, 0);
% \draw[] (2, 0, 2) -- (2, 2, 2);
% \draw[] (0, 0, 2) -- (0, 2, 2);
%
% % Codeword Polytope
%
% \draw[line width=1pt, color=KITblue] (0, 0, 0) -- (2, 0, 2);
% \draw[line width=1pt, color=KITblue] (0, 0, 0) -- (2, 2, 0);
% \draw[line width=1pt, color=KITblue] (0, 0, 0) -- (0, 2, 2);
%
% \draw[line width=1pt, color=KITblue] (2, 0, 2) -- (2, 2, 0);
% \draw[line width=1pt, color=KITblue] (2, 0, 2) -- (0, 2, 2);
%
% \draw[line width=1pt, color=KITblue] (0, 2, 2) -- (2, 2, 0);
%
% % Polytope Annotations
%
% \node[codeword, color=KITred] (c111) at (2, 2, 2) {};% {$\left( 0, 0, 0 \right) $};
% \node[codeword, color=KITred] (c001) at (0, 0, 2) {};% {$\left( 1, 0, 1 \right) $};
% \node[codeword, color=KITred] (c100) at (2, 0, 0) {};% {$\left( 1, 1, 0 \right) $};
% \node[codeword, color=KITred] (c010) at (0, 2, 0) {};% {$\left( 0, 1, 1 \right) $};
%
% \node[color=KITred, left=0cm of c111] {$\left( 1, 1, 1 \right) $};
% \node[color=KITred, right=0cm of c001] {$\left( 0, 0, 1 \right) $};
% \node[color=KITred, right=0.35cm of c100] {$\left( 1, 0, 0 \right) $};
% \node[color=KITred, below=0cm of c010] {$\left( 0, 1, 0 \right) $};
% \end{tikzpicture}
% \caption{Relaxed polytope for $n=3$}
% \end{figure}
% \end{minipage}
% \todo{How is this a relaxation and not just an alternative formulation?
% We have just switched out valid codewords for invalid ones}
% \todo{Is LP Relaxation relevant as theoretical background?}
%\end{frame}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\subsection{ADMM}%
%\label{sub:Alg ADMM}
%
%\begin{frame}[t]
% \frametitle{ADMM Decoding: General Idea}
%
% \todo{TODO}
%\end{frame}
%
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%\begin{frame}[t]
% \frametitle{ADMM Decoding: Algorithm}
%
% \todo{TODO}
%\end{frame}

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