Skip to main content
Bumped by Community user
Bumped by Community user
Bumped by Community user
Bumped by Community user
Bumped by Community user
Bumped by Community user
deleted 429 characters in body
Source Link

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

I am asking this specifically since to me it seems that many of the major textbooks (Karatzas&Shreve, Rogers&Williams) assume or just state as trivial that a weak solution solves the Martingale problem on $C([0,\infty))$ w.r.t. to the filtration $\mathcal{B}_t = \sigma(y(s) | s \le t)$. However this filtration corresponds to $\sigma(X_s | s \le t)$ and not to the filtration $\mathcal{F}_t$ supplied by the weak solution.

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

I am asking this specifically since to me it seems that many of the major textbooks (Karatzas&Shreve, Rogers&Williams) assume or just state as trivial that a weak solution solves the Martingale problem on $C([0,\infty))$ w.r.t. to the filtration $\mathcal{B}_t = \sigma(y(s) | s \le t)$. However this filtration corresponds to $\sigma(X_s | s \le t)$ and not to the filtration $\mathcal{F}_t$ supplied by the weak solution.

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

added 388 characters in body
Source Link

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

I am asking this specifically since to me it seems that many of the major textbooks (Karatzas&Shreve, Rogers&Williams) assume or just state as trivial that a weak solution solves the Martingale problem on $C([0,\infty))$ w.r.t. to the filtration $\mathcal{B}_t = \sigma(y(s) | s \le t)$. However this filtration corresponds to $\sigma(X_s | s \le t)$ and not to the filtration $\mathcal{F}_t$ supplied by the weak solution.

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

Let $(X, W)$, $(\Omega, \mathcal{F}, \mathbb{P})$, $\{\mathcal{F}_t\}$ be a weak solution to an SDE.

Per definition $W$ is an $\mathcal{F}_t$-Brownian motion and both $X$, $W$ are adapted to $\mathcal{F}_t$. In the typical examples for weak solutions one has $\sigma(B_s | s \le t) \subset \sigma(X_s | s \le t)$, since the Brownian motion is constructed in terms of $X$.

Can I, given a weak solution as above, always replace $\mathcal{F}_t$ by $\sigma(X_s | s \le t)$ and still have a weak solution?

I am asking this specifically since to me it seems that many of the major textbooks (Karatzas&Shreve, Rogers&Williams) assume or just state as trivial that a weak solution solves the Martingale problem on $C([0,\infty))$ w.r.t. to the filtration $\mathcal{B}_t = \sigma(y(s) | s \le t)$. However this filtration corresponds to $\sigma(X_s | s \le t)$ and not to the filtration $\mathcal{F}_t$ supplied by the weak solution.

edited title
Link

Let $(X, W)$ be a weak solution to ana SDE. Is $W$ a Brownian motion w.r.t. $\sigma(X_s : s \le t)$?

Source Link
Loading