diff --git a/custom.js b/custom.js
index d24560d..e906c5c 100644
--- a/custom.js
+++ b/custom.js
@@ -1,6 +1,7 @@
window.MathJax = {
tex: {
tags: 'ams'
- }
+ },
+ displayAlign: "left",
+ displayIndent: "0em",
};
-
diff --git a/custom.scss b/custom.scss
index 0eea68b..f429844 100644
--- a/custom.scss
+++ b/custom.scss
@@ -1,3 +1,206 @@
+:root {
+ --col_lightgray: #e7e7e7;
+ --col_blue: #000088;
+ --col_smooth_expost: #a7008b;
+ --col_constant: #dd9002;
+ --col_optimum: #666666;
+ --col_smooth: #187a00;
+ --col_pointwise: #008790;
+ --col_green: #61B94C;
+ --col_orange: #ffa600;
+ --col_yellow: #FCE135;
+ --col_amber_1: #FFF8E0FF;
+ --col_amber_2: #FFEBB2FF;
+ --col_amber_3: #FFDF81FF;
+ --col_amber_4: #FFD44EFF;
+ --col_amber_5: #FFCA27FF;
+ --col_amber_6: #FFC006FF;
+ --col_amber_7: #FFB200FF;
+ --col_amber_8: #FF9F00FF;
+ --col_amber_9: #FF8E00FF;
+ --col_amber_10: #FF6E00FF;
+ --col_blue_1: #E3F2FDFF;
+ --col_blue_2: #BADEFAFF;
+ --col_blue_3: #90CAF8FF;
+ --col_blue_4: #64B4F6FF;
+ --col_blue_5: #41A5F4FF;
+ --col_blue_6: #2096F2FF;
+ --col_blue_7: #1E87E5FF;
+ --col_blue_8: #1976D2FF;
+ --col_blue_9: #1465BFFF;
+ --col_blue_10: #0C46A0FF;
+ --col_blue-grey_1: #EBEEF1FF;
+ --col_blue-grey_2: #CED8DCFF;
+ --col_blue-grey_3: #B0BEC5FF;
+ --col_blue-grey_4: #90A4ADFF;
+ --col_blue-grey_5: #78909BFF;
+ --col_blue-grey_6: #5F7D8BFF;
+ --col_blue-grey_7: #536D79FF;
+ --col_blue-grey_8: #455964FF;
+ --col_blue-grey_9: #37464EFF;
+ --col_blue-grey_10: #263238FF;
+ --col_brown_1: #EEEBE9FF;
+ --col_brown_2: #D7CCC7FF;
+ --col_brown_3: #BBAAA4FF;
+ --col_brown_4: #A0877FFF;
+ --col_brown_5: #8C6D63FF;
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+ --col_cyan_6: #00BBD3FF;
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+ --col_cyan_8: #0097A6FF;
+ --col_cyan_9: #00838EFF;
+ --col_cyan_10: #005F64FF;
+ --col_deep-orange_1: #FAE9E6FF;
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+ --col_deep-orange_10: #BF350CFF;
+ --col_deep-purple_1: #ECE6F6FF;
+ --col_deep-purple_2: #D1C4E9FF;
+ --col_deep-purple_3: #B29DDAFF;
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+ --col_deep-purple_5: #7E57C1FF;
+ --col_deep-purple_6: #6639B7FF;
+ --col_deep-purple_7: #5E34B1FF;
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+ --col_deep-purple_9: #45269FFF;
+ --col_deep-purple_10: #311A92FF;
+ --col_green_1: #E7F4E9FF;
+ --col_green_2: #C7E5C9FF;
+ --col_green_3: #A5D6A6FF;
+ --col_green_4: #80C684FF;
+ --col_green_5: #66BA6AFF;
+ --col_green_6: #4CAE50FF;
+ --col_green_7: #439F46FF;
+ --col_green_8: #388D3BFF;
+ --col_green_9: #2D7D32FF;
+ --col_green_10: #1A5E1FFF;
+ --col_grey_1: #F9F9F9FF;
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+ --col_grey_3: #EDEDEDFF;
+ --col_grey_4: #DFDFDFFF;
+ --col_grey_5: #BDBDBDFF;
+ --col_grey_6: #9E9E9EFF;
+ --col_grey_7: #747474FF;
+ --col_grey_8: #606060FF;
+ --col_grey_9: #414141FF;
+ --col_grey_10: #202020FF;
+ --col_indigo_1: #E7EAF6FF;
+ --col_indigo_2: #C5CAE9FF;
+ --col_indigo_3: #9FA7D9FF;
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+ --col_indigo_5: #5B6BBFFF;
+ --col_indigo_6: #3F51B4FF;
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+ --col_indigo_10: #19227EFF;
+ --col_light-blue_1: #E0F4FEFF;
+ --col_light-blue_2: #B2E5FCFF;
+ --col_light-blue_3: #80D3F9FF;
+ --col_light-blue_4: #4EC3F7FF;
+ --col_light-blue_5: #28B6F6FF;
+ --col_light-blue_6: #02A9F3FF;
+ --col_light-blue_7: #029AE5FF;
+ --col_light-blue_8: #0187D1FF;
+ --col_light-blue_9: #0177BDFF;
+ --col_light-blue_10: #00579AFF;
+ --col_light-green_1: #F1F8E9FF;
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+ --col_light-green_3: #C5E0A5FF;
+ --col_light-green_4: #ADD480FF;
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+ --col_light-green_6: #8BC34AFF;
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+ --col_orange_10: #E55100FF;
+ --col_pink_1: #FCE4EBFF;
+ --col_pink_2: #F8BAD0FF;
+ --col_pink_3: #F38EB1FF;
+ --col_pink_4: #F06192FF;
+ --col_pink_5: #EB3F79FF;
+ --col_pink_6: #E91E63FF;
+ --col_pink_7: #D81A5FFF;
+ --col_pink_8: #C1185AFF;
+ --col_pink_9: #AC1357FF;
+ --col_pink_10: #870D4EFF;
+ --col_purple_1: #F2E5F4FF;
+ --col_purple_2: #E0BEE6FF;
+ --col_purple_3: #CD92D8FF;
+ --col_purple_4: #B967C7FF;
+ --col_purple_5: #AB46BBFF;
+ --col_purple_6: #9B26B0FF;
+ --col_purple_7: #8D24AAFF;
+ --col_purple_8: #7A1FA1FF;
+ --col_purple_9: #6A1A99FF;
+ --col_purple_10: #4A138CFF;
+ --col_red_1: #FFEBEDFF;
+ --col_red_2: #FFCCD2FF;
+ --col_red_3: #EE9999FF;
+ --col_red_4: #E57272FF;
+ --col_red_5: #EE5250FF;
+ --col_red_6: #F34335FF;
+ --col_red_7: #E53934FF;
+ --col_red_8: #D22E2EFF;
+ --col_red_9: #C52727FF;
+ --col_red_10: #B71B1BFF;
+ --col_teal_1: #DFF2F1FF;
+ --col_teal_2: #B2DFDAFF;
+ --col_teal_3: #7FCBC4FF;
+ --col_teal_4: #4CB6ACFF;
+ --col_teal_5: #26A599FF;
+ --col_teal_6: #009687FF;
+ --col_teal_7: #00887AFF;
+ --col_teal_8: #00796BFF;
+ --col_teal_9: #00685BFF;
+ --col_teal_10: #004C3FFF;
+ --col_yellow_1: #FFFDE6FF;
+ --col_yellow_2: #FFF8C4FF;
+ --col_yellow_3: #FFF49DFF;
+ --col_yellow_4: #FFF176FF;
+ --col_yellow_5: #FFED58FF;
+ --col_yellow_6: #FFEB3AFF;
+ --col_yellow_7: #FDD834FF;
+ --col_yellow_8: #FABF2CFF;
+ --col_yellow_9: #F8A725FF;
+ --col_yellow_10: #F47F17FF;
+}
+
/*-- scss:defaults --*/
// $body-bg: #ffffff;
diff --git a/index.qmd b/index.qmd
index 4b56d84..e6a7d4f 100644
--- a/index.qmd
+++ b/index.qmd
@@ -86,10 +86,13 @@ my_bib <- ReadBib("assets/library.bib", check = FALSE)
col_lightgray <- "#e7e7e7"
col_blue <- "#000088"
col_smooth_expost <- "#a7008b"
-col_smooth <- "#187a00"
-col_pointwise <- "#008790"
col_constant <- "#dd9002"
col_optimum <- "#666666"
+col_smooth <- "#187a00"
+col_pointwise <- "#008790"
+col_green <- "#61B94C"
+col_orange <- "#ffa600"
+col_yellow <- "#FCE135"
```
# CRPS Learning
@@ -308,9 +311,9 @@ Weights are updated sequentially according to the past performance of the $K$ ex
That is, a loss function $\ell$ is needed. This is used to compute the **cumulative regret** $R_{t,k}$
-$$
-R_{t,k} = \widetilde{L}_{t} - \widehat{L}_{t,k} = \sum_{i = 1}^t \ell(\widetilde{X}_{i},Y_i) - \ell(\widehat{X}_{i,k},Y_i)
-$${#eq-regret}
+\begin{equation}
+ R_{t,k} = \widetilde{L}_{t} - \widehat{L}_{t,k} = \sum_{i = 1}^t \ell(\widetilde{X}_{i},Y_i) - \ell(\widehat{X}_{i,k},Y_i)\label{eq:regret}
+\end{equation}
The cumulative regret:
@@ -325,13 +328,15 @@ Popular loss functions for point forecasting @gneiting2011making:
$\ell_2$ loss:
-$$\ell_2(x, y) = | x -y|^2$${#eq-elltwo}
+\begin{equation}
+ \ell_2(x, y) = | x -y|^2 \label{eq:elltwo}
+\end{equation}
Strictly proper for *mean* prediction
:::
-::: {.column width="2%"}
+::: {.column width="4%"}
:::
@@ -339,7 +344,9 @@ Strictly proper for *mean* prediction
$\ell_1$ loss:
-$$\ell_1(x, y) = | x -y|$${#eq-ellone}
+\begin{equation}
+ \ell_1(x, y) = | x -y| \label{eq:ellone}
+\end{equation}
Strictly proper for *median* predictions
@@ -400,17 +407,9 @@ In stochastic settings, the cumulative Risk should be analyzed `r Citet(my_bib,
::::
-## Optimality
+## Optimal Convergence
-In stochastic settings, the cumulative Risk should be analyezed @wintenberger2017optimal:
-
-\begin{align}
- \underbrace{\widetilde{\mathcal{R}}_t = \sum_{i=1}^t \mathbb{E}[\ell(\widetilde{X}_{i},Y_i)|\mathcal{F}_{i-1}]}_{\text{Cumulative Risk of Forecaster}} \qquad\qquad\qquad \text{ and } \qquad\qquad\qquad
- \underbrace{\widehat{\mathcal{R}}_{t,k} = \sum_{i=1}^t \mathbb{E}[\ell(\widehat{X}_{i,k},Y_i)|\mathcal{F}_{i-1}]}_{\text{Cumulative Risk of Experts}}
- \label{eq_def_cumrisk}
-\end{align}
-
-There are two problems that an algorithm should solve in iid settings:
+
:::: {.columns}
@@ -423,14 +422,6 @@ There are two problems that an algorithm should solve in iid settings:
\end{equation}
The forecaster is asymptotically not worse than the best expert $\widehat{\mathcal{R}}_{t,\min}$.
-:::
-
-::: {.column width="2%"}
-
-:::
-
-::: {.column width="48%"}
-
### The convex aggregation problem
\begin{equation}
@@ -441,13 +432,14 @@ The forecaster is asymptotically not worse than the best convex combination $\wi
:::
-::::
+::: {.column width="2%"}
-## Optimality
+:::
-Satisfying the convexity property \eqref{eq_opt_conv} comes at the cost of slower possible convergence.
+::: {.column width="48%"}
+
+Optimal rates with respect to selection \eqref{eq_opt_select} and convex aggregation \eqref{eq_opt_conv} `r Citet(my_bib, "wintenberger2017optimal")`:
-According to @wintenberger2017optimal, an algorithm has optimal rates with respect to selection \eqref{eq_opt_select} and convex aggregation \eqref{eq_opt_conv} if
\begin{align}
\frac{1}{t}\left(\widetilde{\mathcal{R}}_t - \widehat{\mathcal{R}}_{t,\min} \right) & =
@@ -466,104 +458,102 @@ Algorithms can statisfy both \eqref{eq_optp_select} and \eqref{eq_optp_conv} dep
- Regularity conditions on $Y_t$ and $\widehat{X}_{t,k}$
- The weighting scheme
-## Optimality
-
-According to @cesa2006prediction EWA \eqref{eq_ewa_general} satisfies the optimal selection convergence \eqref{eq_optp_select} in a deterministic setting if the:
-- Loss $\ell$ is exp-concave
-- Learning-rate $\eta$ is chosen correctly
-
-Those results can be converted to stochastic iid settings @kakade2008generalization, @gaillard2014second.
-
-The optimal convex aggregation convergence \eqref{eq_optp_conv} can be satisfied by applying the kernel-trick. Thereby, the loss is linearized:
-\begin{align}
-\ell^{\nabla}(x,y) = \ell'(\widetilde{X},y) x
-\end{align}
-$\ell'$ is the subgradient of $\ell$ in its first coordinate evaluated at forecast combination $\widetilde{X}$.
-
-Combining probabilistic forecasts calls for a probabilistic loss function
-
-:::: {.notes}
-
-We apply Bernstein Online Aggregation (BOA). It lets us weaken the exp-concavity condition while almost keeping the optimalities \ref{eq_optp_select} and \ref{eq_optp_conv}.
+:::
::::
-## The Continuous Ranked Probability Score
+##
:::: {.columns}
::: {.column width="48%"}
-**An appropriate choice:**
+### Optimal Convergence
-\begin{align*}
- \text{CRPS}(F, y) & = \int_{\mathbb{R}} {(F(x) - \mathbb{1}\{ x > y \})}^2 dx
- \label{eq_crps}
-\end{align*}
+
-It's strictly proper @gneiting2007strictly.
+EWA satisfies optimal selection convergence \eqref{eq_optp_select} in a deterministic setting if:
-Using the CRPS, we can calculate time-adaptive weight $w_{t,k}$. However, what if the experts' performance is not uniform over all parts of the distribution?
+- Loss $\ell$ is exp-concave
+- Learning-rate $\eta$ is chosen correctly
-The idea: utilize this relation:
+Those results can be converted to stochastic iid settings @kakade2008generalization, @gaillard2014second.
-\begin{align*}
- \text{CRPS}(F, y) = 2 \int_0^{1} \text{QL}_p(F^{-1}(p), y) \, d p.
- \label{eq_crps_qs}
-\end{align*}
+Optimal convex aggregation convergence \eqref{eq_optp_conv} can be satisfied by applying the kernel-trick:
+
+\begin{align}
+\ell^{\nabla}(x,y) = \ell'(\widetilde{X},y) x
+\end{align}
+
+$\ell'$ is the subgradient of $\ell$ at forecast combination $\widetilde{X}$.
:::
-::: {.column width="2%"}
+::: {.column width="4%"}
:::
::: {.column width="48%"}
-to combine quantiles of the probabilistic forecasts individually using the quantile-loss (QL):
-\begin{align*}
- \text{QL}_p(q, y) & = (\mathbb{1}\{y < q\} -p)(q - y)
-\end{align*}
+### Probabilistic Setting
-
+
-**But is it optimal?**
+**An appropriate choice:**
-CRPS is exp-concave `r fontawesome::fa("check", fill ="#00b02f")`
+\begin{equation*}
+ \text{CRPS}(F, y) = \int_{\mathbb{R}} {(F(x) - \mathbb{1}\{ x > y \})}^2 dx \label{eq:crps}
+\end{equation*}
-`r fontawesome::fa("arrow-right", fill ="#000000")` EWA \eqref{eq_ewa_general} with CRPS satisfies \eqref{eq_optp_select} and \eqref{eq_optp_conv}
+It's strictly proper @gneiting2007strictly.
-QL is convex, but not exp-concave `r fontawesome::fa("exclamation", fill ="#ffa600")`
+Using the CRPS, we can calculate time-adaptive weights $w_{t,k}$. However, what if the experts' performance varies in parts of the distribution?
-`r fontawesome::fa("arrow-right", fill ="#000000")` Bernstein Online Aggregation (BOA) lets us weaken the exp-concavity condition while almost keeping optimal convergence
+`r fontawesome::fa("lightbulb", fill = col_yellow)` Utilize this relation:
+
+\begin{equation*}
+ \text{CRPS}(F, y) = 2 \int_0^{1} \text{QL}_p(F^{-1}(p), y) dp.\label{eq_crps_qs}
+\end{equation*}
+
+... to combine quantiles of the probabilistic forecasts individually using the quantile-loss QL.
:::
::::
-## CRPS-Learning Optimality
+## CRPS Learning Optimality
+
+::: {.panel-tabset}
+
+## Almost Optimal Convergence
+
+
+`r fontawesome::fa("exclamation", fill = col_orange)` QL is convex, but not exp-concave `r fontawesome::fa("arrow-right", fill ="#000000")` Bernstein Online Aggregation (BOA) lets us weaken the exp-concavity condition. It satisfies that there exist a $C>0$ such that for $x>0$ it holds that
-For convex losses, BOAG satisfies that there exist a $C>0$ such that for $x>0$ it holds that
\begin{equation}
P\left( \frac{1}{t}\left(\widetilde{\mathcal{R}}_t - \widehat{\mathcal{R}}_{t,\pi} \right) \leq C \log(\log(t)) \left(\sqrt{\frac{\log(K)}{t}} + \frac{\log(K)+x}{t}\right) \right) \geq
- 1-e^{x}
+ 1-e^{-x}
\label{eq_boa_opt_conv}
\end{equation}
+
`r fontawesome::fa("arrow-right", fill ="#000000")` Almost optimal w.r.t *convex aggregation* \eqref{eq_optp_conv} @wintenberger2017optimal.
The same algorithm satisfies that there exist a $C>0$ such that for $x>0$ it holds that
\begin{equation}
P\left( \frac{1}{t}\left(\widetilde{\mathcal{R}}_t - \widehat{\mathcal{R}}_{t,\min} \right) \leq
C\left(\frac{\log(K)+\log(\log(Gt))+ x}{\alpha t}\right)^{\frac{1}{2-\beta}} \right) \geq
- 1-e^{x}
+ 1-2e^{-x}
\label{eq_boa_opt_select}
\end{equation}
-if $Y_t$ is bounded, the considered loss $\ell$ is convex $G$-Lipschitz and weak exp-concave in its first coordinate.
+if $Y_t$ is bounded, the considered loss $\ell$ is convex $G$-Lipschitz and weak exp-concave in its first coordinate.
-This is for losses that satisfy **A1** and **A2**.
+`r fontawesome::fa("arrow-right", fill ="#000000")` Almost optimal w.r.t *selection* \eqref{eq_optp_select} @gaillard2018efficient.
+
+`r fontawesome::fa("arrow-right", fill ="#000000")` We show that this holds for QL under feasible conditions.
+
+## Conditions + Lemma
-## CRPS-Learning Optimality
:::: {.columns}
@@ -624,8 +614,7 @@ QL is Lipschitz continuous:
::::
-
-## CRPS-Learning Optimality
+## Proposition + Theorem
:::: {.columns}
@@ -674,6 +663,13 @@ $$\widehat{\mathcal{R}}_{t,\min} = 2\overline{\widehat{\mathcal{R}}}^{\text{QL}}
::::
+::::
+
+:::: {.notes}
+
+We apply Bernstein Online Aggregation (BOA). It lets us weaken the exp-concavity condition while almost keeping the optimalities \ref{eq_optp_select} and \ref{eq_optp_conv}.
+
+::::
## A Probabilistic Example
@@ -797,13 +793,17 @@ ggplot() +
:::
-## The Smoothing Procedure
+## The Smoothing Procedures
+
+::: {.panel-tabset}
+
+## Penalized Smoothing
:::: {.columns}
::: {.column width="48%"}
-We are using penalized cubic b-splines:
+Penalized cubic B-Splines for smoothing weights:
Let $\varphi=(\varphi_1,\ldots, \varphi_L)$ be bounded basis functions on $(0,1)$ Then we approximate $w_{t,k}$ by
@@ -811,7 +811,7 @@ Let $\varphi=(\varphi_1,\ldots, \varphi_L)$ be bounded basis functions on $(0,1)
w_{t,k}^{\text{smooth}} = \sum_{l=1}^L \beta_l \varphi_l = \beta'\varphi
\end{align}
-with parameter vector $\beta$. The latter is estimated penalized $L_2$-smoothing which minimizes
+with parameter vector $\beta$. The latter is estimated to penalize $L_2$-smoothing which minimizes
\begin{equation}
\| w_{t,k} - \beta' \varphi \|^2_2 + \lambda \| \mathcal{D}^{d} (\beta' \varphi) \|^2_2
@@ -820,7 +820,7 @@ with parameter vector $\beta$. The latter is estimated penalized $L_2$-smoothing
with differential operator $\mathcal{D}$
-Smoothing can be applied ex-post or inside of the algorithm ( `r fontawesome::fa("arrow-right", fill ="#000000")` [Simulation](#simulation)).
+Computation is easy, since we have an analytical solution
:::
@@ -840,14 +840,119 @@ We receive the constant solution for high values of $\lambda$ when setting $d=1$
::::
+## Basis Smoothing
+
+:::: {.columns}
+
+::: {.column width="48%"}
+
+Represent weights as linear combinations of bounded basis functions:
+
+\begin{equation}
+ w_{t,k} = \sum_{l=1}^L \beta_{t,k,l} \varphi_l = \boldsymbol \beta_{t,k}' \boldsymbol \varphi
+\end{equation}
+
+A popular choice are are B-Splines as local basis functions
+
+$\boldsymbol \beta_{t,k}$ is calculated using a reduced regret matrix:
+
+\begin{equation}
+ \underbrace{\boldsymbol r_{t}}_{\text{LxK}} = \frac{L}{P} \underbrace{\boldsymbol B'}_{\text{LxP}} \underbrace{\left({\boldsymbol{QL}}_{\mathcal{P}}^{\nabla}(\widetilde{\boldsymbol X}_{t},Y_t)- {\boldsymbol{QL}}_{\mathcal{P}}^{\nabla}(\widehat{\boldsymbol X}_{t},Y_t)\right)}_{\text{PxK}}
+\end{equation}
+
+`r fontawesome::fa("arrow-right", fill ="#000000")` $\boldsymbol r_{t}$ is transformed from PxK to LxK
+
+If $L = P$ it holds that $\boldsymbol \varphi = \boldsymbol{I}$
+For $L = 1$ we receive constant weights
+
+:::
+
+::: {.column width="2%"}
+
+:::
+
+::: {.column width="48%"}
+
+Weights converge to the constant solution if $L\rightarrow 1$
+
+
+