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Theory and applications of probability and stochastic processes: e.g. central limit theorems, large deviations, stochastic differential equations, models from statistical mechanics, queuing theory.
2
votes
When is a function on symmetric positive definite matrices an expectation of Gaussian?
Here's an approach to determine if $\det(C)$ is of this form with $F$ analytic and $n=2$.
By Sylvester's criterion a matrix $\begin{pmatrix} a& b \\ b & c\end{pmatrix}$ is symmetric positive semidefin …
1
vote
Probability of a given string being a substring of another string
Let $A_t$ be the event that $S_1$ is a substring of $S_2$, $S_2=pS_1q$, where the length of $p$ is $t$.
Then the probability of $\cup_t A_t$ can be found by inclusion-exclusion as
$$\sum P(A_t)-\sum P …
3
votes
A definite integral related to sample variances of bivariate Gaussians
It seems that Wolfram Alpha understands this integral.
Its answers are given
in terms of modified Bessel functions of the first kind $I_k$.
It seems that the result is, for
$A(k,c):=I(n,c)$, with $n …
3
votes
1
answer
225
views
Brownian level sets and continuous functions
Let $V_t$ and $W_t$ be independent standard Wiener processes ($t\ge 0$, $W_t,V_t\in\mathbb R$).
Let $C$ be the event that there is a continuous function $f$ such that for all $s$, $t$,
$$
W_t=W_s\iff …
1
vote
Is it true that the quantile function of an $L^1$ random variable is $L^2(]0,1[)$?
Sinve you mentioned famous examples, here is a famous counterexample: power law distributions.
3
votes
Distinguishing between urn probability models
As you point out, the colors observed will have the same distribution with each of these models.
Statistical tests involve asking
"what is the probability of what is observed according to various …
4
votes
Accepted
When are events in tail $\sigma$-algebra the limsup of some sequence of events?
No, let $\mathcal S_0=\{\{0,1\},\emptyset\}$ and let
$\mathcal S_1$ be the powerset of $\{0,1\}$. Let
$\mathcal F_n=\mathcal S_0^{n-1}\times\mathcal S_1
\times\mathcal S_0^{\infty}$.
Let us write $X …
2
votes
Covering subset with large probability
It is true. Let $k=\binom{N}{N/2-c\sqrt N}$ and let $K$ be a randomly* selected subset of $k$ of size $k\lambda$. Then conditionally on $|X|>N/2-c\sqrt N$, the difference $|X|-(N/2-c\sqrt N)$ is unbou …
1
vote
Accepted
Finding a distribution satisfying uncountably many constraints. Any relevant references?
It seems that in general this is an almost arbitrarily hard problem.
Consider the simpler countably infinite case $X=\mathbb N$, $Y=\{0,1\}$.
Thus $H=\{x:h(x)=1\}$ is a "random set".
Fix $g:X\to\{0, …
1
vote
Is stopped brownian motion not a martingale?
Let $a=1$ or any other positive constant. Then
$$E(M(\inf\{t:M(t)\ge a\}))=a$$
since
$$P(M(\inf\{t:M(t)\ge a\})=a)=1.$$
And $a\ne M(t)$ with positive probability (actually probability 1).
0
votes
Minimal coupling
Yes, your bound is optimal and here's how to attain it.
Fix a linear ordering $L$ of $\Omega$. Pick a number $x \in [0,1]$ under the uniform measure and the value of our coupling shall be $(M(x),N(x) …
1
vote
Accepted
algebraic tail of a random variable
It just means that
$$\mu\left(\{f: K_f>y\}\right)<\frac{\alpha}{y^\beta}$$
and
$$\mu\left(\{f: \rho(x_0,f(x_0))>y\}\right)<\frac{\alpha}{y^\beta}$$
5
votes
Accepted
About another potential characterization of normal numbers
Yes, for integer $b$ it's a reformulation of, and exactly the same as, normality to base $b$.
Wikipedia even has a section of its article about normal numbers stating exactly this, and giving credit …
2
votes
Accepted
Where does the expected value in the restatement of the pseudoregret come from?
Since
$$E(X_{I_t}\mid I_t)=\mu_{I_t},$$
by iterated expectation
$$E(X_{I_t})=E(E(X_{I_t}\mid I_t)) = E(\mu_{I_t}),$$
from which we have the desired equality.
1
vote
Are there any continuous-time stochastic processes in which transition probabilities are dis...
One example type is a jump process that jumps at certain predetermined times, as in @AnthonyQuas' comment.
For instance, a stock price that can only make jumps when markets open, like New Zealand Sto …