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A stochastic process is a collection of random variables usually indexed by a totally ordered set.
1
vote
Accepted
Does $L^2$ progressive measurable processes form a Hilbert space?
The answer is indeed yes, as every adapted measurable real-valued process admits a progressively measurable modification. This is classical Theorem due to Paul-André Meyer (cf. Paul A. Meyer. Probabil …
4
votes
Reflected Brownian Motion
As your reflected Brownian motion is nothing else then the absolute value of a Brownian motion you have $$ \{t \in [0,T] : Y_t = 0\} = \{t \in [0,T] : \vert W_t \vert= 0\} = \{t \in [0,T] : W_t …
1
vote
calculate all the equivalent martingale measures
One possible approach is to use the fact that the density process $\left. Z_t =\frac{d\mathcal{Q}}{d\mathcal{P}} \right\vert_{\mathcal{F}_t}$ for every equivalent local martingale measure $\mathcal{Q} …
1
vote
Accepted
Is $B(t-1)$ an Ito process?
Note that for fixed $t_0$, we have by the martingale representation theorem that
$$Y_{t_0} = \int_0^{t_0} I\bigl( s \in [0,t_0-1) \bigr) \, dB_s.$$
In particular that for $t_0\leq 1$ the indicator y …
1
vote
Accepted
Definition: Grigelionis Process?
A Grigelionis process is a special semimartingale with absolutely continuous integral characteristics (in time). This is insofar a generalization of a Lévy process, as Lévy processes can be characteri …
2
votes
Accepted
Optimal control / Portoflio optimization: Maximize expected utility of total consumption
The problem as stated has no solution except in the special case where it is optimal not to consume at all.
To see this, note that the payoff depends on the consumption rate process $c(t)$ only throu …
1
vote
Representation theorem for continuous uniformly integrable martingales
I think question 1) is reasonably answered by Wolfgang Loehr in his comment. To get a counterexample for your claims in 2), just set $a_u=W_u^2-u$ for your Brownian motion. Ito's formula gives you the …
1
vote
Accepted
BSDE without volatility
I am not sure if I understand your question correctly. A typical Brownian BSDE has the form
$$dY_t = f(\omega, t, Y_t, Z_t)dt - Z_t dW_t$$
with terminal condition
$$Y_T = \xi \in \mathcal{F}^{W}_T$$
w …
4
votes
Accepted
Stochastic processes having Markov kernels
No, that both processes have the same one-dimensional marginals is not sufficient. In contrary, when $X$ is an arbitrary elliptic Itô-process, you can always find a Markov process with the same margin …
4
votes
Accepted
On martingale representation theorem
No, but under some regularity conditions you might represent $a(t)$ in terms of Malliavin calculus by means of the Clark-Ocone formula (see e.g. the Lecture notes by Eulalia Nualart, Section 1.5.3.)
9
votes
Accepted
Can all local martingales be represented using only Brownian motion and finite variation pro...
First, a martingale is always only specified with respect to a filtration, and so is thus a local martingale. You do not specify any filtration in your problem, so I assume you mean the natural filtra …
2
votes
Malliavin derivative under change of measure
Here an answer for the case with determinist drift as mentioned in the edit. (Note: I fail to see why to use different notations for $F$ and $\tilde{F}$ as it is the same process)
As
$$ dF_t = \mu_t …
2
votes
$\lim_{t\rightarrow 0}P\left(X_t >0\right)=\frac 1 2$ for continuous semimartingales?
The proof is not correct, as without additional integrability condition you will not be able to conclude that $g_n \in L^2$ for $n$ large enough, and therefore the $L^2$ convergence argument fails. As …
3
votes
Accepted
Question about the exit time of a time-homogeneous Itô diffusion
You can solve this by reducing it to a problem of Brownian motion: Define the scale function
$\varsigma(x) = \int_{X_0}^x e^{-2\int_{X_0}^y \frac{b(z)}{\sigma^2(z)} dz} dy$
the process
$M_t = \var …
3
votes
Properties preserved under passage to augmented filtration
Hi lpdbw,
I think this is a very interesting questions, here at least a partial answer; It depends heavily on the little word "strong" in parentheseis.
Assuming that $(X_t)$ is strong Markov, the an …