Improve prop2 proof
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10
index.qmd
10
index.qmd
@@ -1422,25 +1422,25 @@ $$\widehat{\mathcal{R}}_{t,\min} = 2\overline{\widehat{\mathcal{R}}}^{\text{QL}}
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First, rewrite $QL_p$ using the check function:
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\begin{align}
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\rho_p(z) = z(1(0 < z) - p) \label{eq:check}
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\rho_p(z) = z(\mathbb{1}(0 < z) - p) \label{eq:check}
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\end{align}
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\begin{align}
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QL_p(x, y) &= (\mathbf1(y < x) - p)(x - y) \\
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QL_p(x, y) &= (\mathbb{1}(y < x) - p)(x - y) \\
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&= \rho_p(x-y)
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\end{align}
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Now we can express the quantile risk as:
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\begin{align}
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\mathcal{Q}_p(x) = E[\rho_p(x-y)] = ∫ \rho_p(x-y)f(y)dy
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\mathcal{Q}_p(x) = \mathbb{E}[\rho_p(x-y)] = ∫ \rho_p(x-y)f(y)dy
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\end{align}
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This integral form is where the convolution becomes apparent. A convolution of functions is defined as:
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\begin{align}
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(g * h)(x) &= ∫ g(z)h(x - z)dz \\
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&= ∫ h(x - z)g(z)dz
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&= ∫ g(x - z)h(z)dz
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\end{align}
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They are commutative.
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@@ -1477,7 +1477,7 @@ To find $\mathcal{Q}''_p(x)$ we rewrite \eqref{eq:check}:
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The function $\rho'_p(z)$ jumps from $-p$ to $1-p$ at $0$. So:
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\begin{align}
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\rho''_p(x) = \delta_0(z) \quad \text{Dirac Delta}
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\rho''_p(x) = \delta_0(z) \quad \text{(Dirac Delta)}
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\end{align}
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Now the magical part <i class="fa fa-fw fa-wand-magic-sparkles" style="color:var(--col_amber_6);"></i>:
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