From 16555851b6514a736c5c9d8e73de7da7fc9b6288 Mon Sep 17 00:00:00 2001 From: Prefetch Date: Thu, 20 Oct 2022 18:25:31 +0200 Subject: Migrate from 'jekyll-katex' to 'kramdown-math-sskatex' --- source/know/concept/stochastic-process/index.md | 48 ++++++++++++------------- 1 file changed, 24 insertions(+), 24 deletions(-) (limited to 'source/know/concept/stochastic-process') diff --git a/source/know/concept/stochastic-process/index.md b/source/know/concept/stochastic-process/index.md index dc3d30e..68f028d 100644 --- a/source/know/concept/stochastic-process/index.md +++ b/source/know/concept/stochastic-process/index.md @@ -9,24 +9,24 @@ categories: layout: "concept" --- -A **stochastic process** $X_t$ is a time-indexed +A **stochastic process** $$X_t$$ is a time-indexed [random variable](/know/concept/random-variable/), -$\{ X_t : t > 0 \}$, i.e. a set of (usually correlated) -random variables, each labelled with a unique timestamp $t$. +$$\{ X_t : t > 0 \}$$, i.e. a set of (usually correlated) +random variables, each labelled with a unique timestamp $$t$$. Whereas "ordinary" random variables are defined on -a probability space $(\Omega, \mathcal{F}, P)$, +a probability space $$(\Omega, \mathcal{F}, P)$$, stochastic process are defined on -a **filtered probability space** $(\Omega, \mathcal{F}, \{ \mathcal{F}_t \}, P)$. -As before, $\Omega$ is the sample space, -$\mathcal{F}$ is the event space, -and $P$ is the probability measure. +a **filtered probability space** $$(\Omega, \mathcal{F}, \{ \mathcal{F}_t \}, P)$$. +As before, $$\Omega$$ is the sample space, +$$\mathcal{F}$$ is the event space, +and $$P$$ is the probability measure. -The **filtration** $\{ \mathcal{F}_t : t \ge 0 \}$ -is a time-indexed set of [$\sigma$-algebras](/know/concept/sigma-algebra/) on $\Omega$, +The **filtration** $$\{ \mathcal{F}_t : t \ge 0 \}$$ +is a time-indexed set of [$$\sigma$$-algebras](/know/concept/sigma-algebra/) on $$\Omega$$, which contains at least all the information generated -by $X_t$ up to the current time $t$, -and is a subset of $\mathcal{F}_t$: +by $$X_t$$ up to the current time $$t$$, +and is a subset of $$\mathcal{F}_t$$: $$\begin{aligned} \mathcal{F} @@ -34,18 +34,18 @@ $$\begin{aligned} \supseteq \sigma(X_s : 0 \le s \le t) \end{aligned}$$ -In other words, $\mathcal{F}_t$ is the "accumulated" $\sigma$-algebra -of all information extractable from $X_t$, -and hence grows with time: $\mathcal{F}_s \subseteq \mathcal{F}_t$ for $s < t$. -Given $\mathcal{F}_t$, all values $X_s$ for $s \le t$ can be computed, -i.e. if you know $\mathcal{F}_t$, then the present and past of $X_t$ can be reconstructed. - -Given any filtration $\mathcal{H}_t$, a stochastic process $X_t$ -is said to be *"$\mathcal{H}_t$-adapted"* -if $X_t$'s own filtration $\sigma(X_s : 0 \le s \le t) \subseteq \mathcal{H}_t$, -meaning $\mathcal{H}_t$ contains enough information -to determine the current and past values of $X_t$. -Clearly, $X_t$ is always adapted to its own filtration. +In other words, $$\mathcal{F}_t$$ is the "accumulated" $$\sigma$$-algebra +of all information extractable from $$X_t$$, +and hence grows with time: $$\mathcal{F}_s \subseteq \mathcal{F}_t$$ for $$s < t$$. +Given $$\mathcal{F}_t$$, all values $$X_s$$ for $$s \le t$$ can be computed, +i.e. if you know $$\mathcal{F}_t$$, then the present and past of $$X_t$$ can be reconstructed. + +Given any filtration $$\mathcal{H}_t$$, a stochastic process $$X_t$$ +is said to be *"$$\mathcal{H}_t$$-adapted"* +if $$X_t$$'s own filtration $$\sigma(X_s : 0 \le s \le t) \subseteq \mathcal{H}_t$$, +meaning $$\mathcal{H}_t$$ contains enough information +to determine the current and past values of $$X_t$$. +Clearly, $$X_t$$ is always adapted to its own filtration. Filtration and their adaptations are very useful for working with stochastic processes, -- cgit v1.3