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authorStratis Ioannidis <stratis@stratis-Latitude-E6320.(none)>2013-07-06 16:04:12 -0700
committerStratis Ioannidis <stratis@stratis-Latitude-E6320.(none)>2013-07-06 16:04:12 -0700
commit77a44d83502e10a666e68cec8fdddccf76719b3b (patch)
tree7eef0aee265d43509bf893ba01d3df27afebd248 /problem.tex
parent49995b4aecef20bd138dea3bf66d55dfccc8164d (diff)
downloadrecommendation-77a44d83502e10a666e68cec8fdddccf76719b3b.tar.gz
3.2
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@@ -56,7 +56,7 @@ $D$-optimality criterion
Note that the estimator $\hat{\beta}$ is a linear map of $y_S$; as $y_S$ is a multidimensional normal r.v., so is $\hat{\beta}$ (the randomness coming from the noise terms $\varepsilon_i$ and the prior on $\beta$).
In particular, $\hat{\beta}$ has
-covariance $\sigma^2(R+\T{X_S}X_S)^{-1}$. As such, maximizing $I(\beta;y_S)$ can alternatively be seen as a means of reducing the uncertainty on estimator $\hat{\beta}$ my minimizing the product of the eigenvalues of its covariance.
+covariance $\sigma^2(R+\T{X_S}X_S)^{-1}$. As such, maximizing $I(\beta;y_S)$ can alternatively be seen as a means of reducing the uncertainty on estimator $\hat{\beta}$ by minimizing the product of the eigenvalues of its covariance.
%An alternative interpretation, given that $(R+ \T{X_S}X_S)^{-1}$ is the covariance of the estimator $\hat{\beta}$, is that it tries to minimize the
%which is indeed a function of the covariance matrix $(R+\T{X_S}X_S)^{-1}$.
@@ -124,9 +124,9 @@ In particular, consider the greedy algorithm in which, for
$S\subseteq\mathcal{N}$ the set constructed thus far, the next
element $i$ included is the one which maximizes the
\emph{marginal-value-per-cost}, \emph{i.e.},
-\begin{align}
- i = \argmax_{j\in\mathcal{N}\setminus S}\frac{V(S\cup\{i\}) - V(S)}{c_i}\label{greedy}
-\end{align}
+%\begin{align}
+ $ i = \argmax_{j\in\mathcal{N}\setminus S}{(V(S\cup\{i\}) - V(S))}/{c_i}.$ %\label{greedy}
+%\end{align}
This is repeated until adding an element in $S$ exceeds the budget
$B$. Denote by $S_G$ the set constructed by this heuristic and let
$i^*=\argmax_{i\in\mathcal{N}} V(\{i\})$ be the element of maximum singleton value. Then,