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ludwigbothmann committed Aug 29, 2024
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\end{figure}


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38 changes: 17 additions & 21 deletions slides/regularization/slides-regu-bias-variance.tex
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}{% Lecture title
Bias-variance Tradeoff
}{% Relative path to title page image: Can be empty but must not start with slides/
figure_man/biasvariance_scheme.png
slides/regularization/figure_man/bv_anim_1.pdf
}{
\item Understand the bias-variance trade-off
\item Know the definition of model bias, estimation bias, and estimation variance
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In this slide set, we will visualize the bias-variance trade-off. \\
\lz

First, we start with a DGP $\Pxy$ and a suitable loss function $L:\mathbb{R}^g\times\mathbb{R}^g\rightarrow\mathbb{R}$ where $\mathbb{R}^g$ is numerical encoding of $\Yspace$. We measure the distance between models $f:\Xspace\rightarrow\mathbb{R}^g$ via $$d(f, f^\prime) = \E_{\xv\sim\mathbb{P}_{\xv}}\left[L(f(\xv), f^\prime(\xv)\right].$$
We restrict our attention to losses for which $d$ becomes a metric, e.g., L1-loss, L2-loss, etc. \\
We consider a DGP $\Pxy$ with $\Yspace \subset \R$ and the L2 loss $L$. We measure the distance between models $f:\Xspace\rightarrow\mathbb{R}^g$ via $$d(f, f^\prime) = \E_{\xv\sim\mathbb{P}_{\xv}}\left[L(f(\xv), f^\prime(\xv)\right].$$ \\
\lz
We define $\ftrue$ as the risk minimizer such that $$\ftrue \in \argmin_{f \in \Hspace_0} \E_{\xy \sim \Pxy}\left[L(y, f(\xv))\right]$$
We define $\fbayes_0$ as the risk minimizer such that $$\fbayes_0 \in \argmin_{f \in \Hspace_0} \E_{\xy \sim \Pxy}\left[L(y, f(\xv))\right]$$

where $\Hspace_0 = \left\{f:\Xspace\rightarrow\mathbb{R}^g\vert\; d(\underline{0}, f) < \infty \right\}$ and $\underline{0}:\Xspace\rightarrow\{0\}$.
where $\Hspace_0 = \left\{f:\Xspace\rightarrow\mathbb{R}\vert\; d(\underline{0}, f) < \infty \right\}$ and $\underline{0}:\Xspace\rightarrow\{0\}$.

\framebreak

In practice, our model space $\Hspace$ usually is a proper subset of $\Hspace_0$ and in general $\ftrue \notin \Hspace.$\\
Our model space $\Hspace$ usually is a proper subset of $\Hspace_0$ and in general $\fbayes_0 \notin \Hspace.$\\
We define $\fbayes$ as the risk minimizer in $\Hspace,$ i.e.,
$$\fbayes \in \argmin_{f \in \Hspace} \E_{\xy \sim \Pxy}\left[L(f(\xv, y)\right].$$
It is the function in $\Hspace$ closest to $\ftrue$, and we call $d(\ftrue, \fbayes)$ the model bias.
$\fbayes \in \Hspace$ is closest to $\fbayes_0$, and we call $d(\fbayes_0, \fbayes)$ the model bias.

\begin{center}
\includegraphics[width=0.5\textwidth]{figure_man/to_replace_model_bias.png}
\includegraphics[width=0.5\textwidth]{slides/regularization/figure_man/bv_anim_6.pdf}
\end{center}
\framebreak
We can further restrict the model space such that $\Hspace_R$ is a proper subset of $\Hspace.$
By regularizing our model, we further restrict the model space so that $\Hspace_R$ is a proper subset of $\Hspace.$
We define $\fbayes_R$ as the risk minimizer in $\Hspace_R,$ i.e.,
$$\fbayes_R \in \argmin_{f \in \Hspace_R} \E_{\xy \sim \Pxy}\left[L(f(\xv, y)\right].$$
It is the function in $\Hspace_R$ closest to $\ftrue$, and we call $d(\fbayes_R, \fbayes)$ the estimation bias.
$\fbayes_R \in \Hspace_R$ is closest to $\ftrue$, and we call $d(\fbayes_R, \fbayes)$ the estimation bias.
\begin{center}
\includegraphics[width=0.49\textwidth]{figure_man/to_replace_estimation_bias.png}
\includegraphics[width=0.49\textwidth]{slides/regularization/figure_man/bv_anim_5.pdf}
\end{center}
\framebreak

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\begin{columns}[onlytextwidth,T]
\column{0.5\linewidth}

\includegraphics[width=1.0\textwidth]{figure_man/to_replace_sampling.png}
\includegraphics[width=1.0\textwidth]{slides/regularization/figure_man/bv_anim_4.pdf}

\column{0.5\linewidth}
\column{0.45\linewidth}
\lz
Note: \\
\begin{itemize}
\item $L:\Yspace\times\R^g\rightarrow\R$ is overloaded.
\item The samples are only shown in the visualization for didactic purposes but are not an element of $\Hspace.$
\end{itemize}
Note that the realization is only shown in the visualization for didactic purposes but is not an element of $\Hspace_0.$

\end{columns}

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\begin{columns}[onlytextwidth,T]
\column{0.5\linewidth}

\includegraphics[width=1.0\textwidth]{figure_man/to_replace_estimation_variance.png}
\includegraphics[width=1.0\textwidth]{slides/regularization/figure_man/bv_anim_3.pdf}

\column{0.5\linewidth}
\lz
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\begin{columns}[onlytextwidth,T]
\column{0.48\linewidth}

\includegraphics[width=1.0\textwidth]{figure_man/to_replace_estimation_variance_res.png}
\includegraphics[width=1.0\textwidth]{slides/regularization/figure_man/bv_anim_2.pdf}

\column{0.5\linewidth}
\lz
\begin{itemize}
\item We can measure the spread of sampled $\fh_R$ around $\fbayes_R$ via $\delta = \var_\D\left[d(\fbayes, \fh_R)\right]$ which we also call estimation variance.
\item We can measure the spread of sampled $\fh_R$ around $\fbayes_R$ via $\delta = \var_\D\left[d(\fbayes_R, \fh_R)\right]$ which we also call estimation variance.
\item We observe that the increased bias results in a smaller estimation variance in $\Hspace_R$ compared to $\Hspace.$
\end{itemize}
\end{columns}
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