Added footnote about discrete -> continuous; Added quotation marks; minor other changes
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@ -97,6 +97,11 @@
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long = probability density function
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}
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\DeclareAcronym{PMF}{
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short = PMF,
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long = probability mass function
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}
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%
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% V
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%
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@ -25,14 +25,14 @@ available optimization algorithms.
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Generally, the original decoding problem considered is either the \ac{MAP} or
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the \ac{ML} decoding problem:%
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%
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\begin{align*}
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\begin{align}
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\hat{\boldsymbol{c}}_{\text{\ac{MAP}}} &= \argmax_{\boldsymbol{c} \in \mathcal{C}}
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p_{\boldsymbol{C} \mid \boldsymbol{Y}} \left(\boldsymbol{c} \mid \boldsymbol{y}
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\right)\\
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\right) \label{eq:dec:map}\\
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\hat{\boldsymbol{c}}_{\text{\ac{ML}}} &= \argmax_{\boldsymbol{c} \in \mathcal{C}}
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f_{\boldsymbol{Y} \mid \boldsymbol{C}} \left( \boldsymbol{y} \mid \boldsymbol{c}
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\right)
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.\end{align*}%
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\right) \label{eq:dec:ml}
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.\end{align}%
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%
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The goal is to arrive at a formulation, where a certain objective function
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$g : \mathbb{R}^n \rightarrow \mathbb{R}^n $ must be minimized under certain constraints:%
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@ -707,7 +707,11 @@ non-convex optimization formulation of the \ac{MAP} decoding problem.
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In order to derive the objective function, the authors begin with the
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\ac{MAP} decoding rule, expressed as a continuous maximization problem%
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\footnote{The }%
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\footnote{The expansion of the domain to be continuous doesn't constitute a
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material difference.
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The only change is that what previously were \acp{PMF} now have to be expressed
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in terms of \acp{PDF}}
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over $\boldsymbol{x}$
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:%
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%
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\begin{align}
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@ -726,7 +730,7 @@ The likelihood $f_{\boldsymbol{Y} \mid \tilde{\boldsymbol{X}}}
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determined by the channel model.
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The prior \ac{PDF} $f_{\tilde{\boldsymbol{X}}}\left( \tilde{\boldsymbol{x}} \right)$ is also
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known, as the equal probability assumption is made on
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$\mathcal{C}\left( \boldsymbol{H} \right)$.
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$\mathcal{C}$.
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However, since the considered domain is continuous,
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the prior \ac{PDF} cannot be ignored as a constant during the minimization
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as is often done, and has a rather unwieldy representation:%
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@ -843,14 +847,14 @@ The second step thus becomes%
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\hspace{5mm}\gamma > 0,\text{ small}
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.\end{align*}
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%
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While the approximation of the prior \ac{PDF} made in \ref{eq:prox:prior_pdf_approx}
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While the approximation of the prior \ac{PDF} made in equation (\ref{eq:prox:prior_pdf_approx})
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theoretically becomes better
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with larger $\gamma$, the constraint that $\gamma$ be small is important,
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as it keeps the effect of $h\left( \boldsymbol{x} \right) $ on the landscape
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of the objective function small.
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Otherwise, unwanted stationary points, including local minima, are introduced.
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The authors say that in practice, the value of $\gamma$ should be adjusted
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according to the decoding performance \cite[Sec. 3.1]{proximal_paper}.
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The authors say that ``in practice, the value of $\gamma$ should be adjusted
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according to the decoding performance.'' \cite[Sec. 3.1]{proximal_paper}.
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%The components of the gradient of the code-constraint polynomial can be computed as follows:%
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%%
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