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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.
1
vote
Accepted
Bounded convergence for expectation of random variables
Yes, it's true.
You only need basic facts about convergence in distribution (of real rvs). Both can be e.g. be found in Billingsley's book "Convergence of Probability Measures".
Let $(Y_n)$ be a s …
7
votes
Accepted
Birthday problem with unequal probability: expected number of draws before the $m$-th collis...
(1) Simple bounds:
For $m=1$ (see here
(or here and here)) the inequalities
\begin{align*}
\sqrt{\frac{\pi}{2}}{1\over \lVert p\rVert_2}&\leq \mathbb{E}(M_1)\leq \sqrt{\frac{\pi}{2}}{1 \over \lVer …
8
votes
Expected supremum of average?
Here is an "arbirarily nice" example with closed form results.
Let $X_1,X_2,\ldots$ be i.i.d. real random variables with partial sums $S_k:=\sum_{i=1}^kX_i$ and let $M_n:=\sup_{k\leq n} \frac{S_k}{k} …
6
votes
Probability of getting exactly one head and $k$-wise independence
Here is a solution for even $k\leq d$.
I. A lower bound for even $k$.
Simple lower bound (for $k$ even) follows from standard combinatorics of events
and Bonferroni's inequalities. We need the followi …
2
votes
Accepted
Sum of inverse of multinomial coefficients
I add two hopefully useful remarks.
I consider the general situation. In the sequel $k\geq 1$ and $\lambda=(\lambda_1,\ldots,\lambda_{k+1})$ are fixed, $s:=\sum_{i=1}^{k+1}\lambda_i$ and $n\geq s$.
…
1
vote
Accepted
Arcsine law for Brownian motion with drift
Here is a simple description:
$$Z\stackrel{d}{=}A\cdot Y_m$$ i.e. $Z$ is distributed as the product of two random variables, where the the factors are independent, $A$ is $\arcsin$-distributed, and $ …
3
votes
Accepted
Birthday inequality for non-uniform distributions for fixed collision probability (random al...
I reformulate slightly, please check.
You are considering a sequence $X_1,X_2,\ldots$ of (discrete) i.i.d
random variables
and want an upper bound for the probability $\mathbb{P}(R>n)$
in terms of $ …
1
vote
Dice waiting time for $5,6$ is smaller than for $6,6$
Here is a completely elementary argument.
Let $T_{56}:=\tau_{56}+1, T_{66}:=\tau_{66}+1$ be the first times
the patterns have appeared, i.e.
$$T_{56}:=\inf\{ n \geq 2\;:\;X_{n-1}=5,\,X_n=6 \}$$ etc. …
1
vote
Mixed moments for the birthday problem
Here is an approach via Lagrange inversion.
Let $N$ denote the time of the first repeat, and let $T(z)$ (the ``tree function'') be the formal power series satisfying $T(z)=z\,e^{T(z)}$.
If $F$ is a …
4
votes
Accepted
The probability density function of the number of coins to first fill one box of $N$
(I change notation from $N,C$ to $n,c$ since I use capitals throughout to denote rvs).
Let $X_i$ be the random variable "number of the box the $i$-th coin", then $X_1,X_2,\ldots$ is an i.i.d. sequenc …
3
votes
Accepted
Birthday problem extension to unequal probabilities and multiple collisions
Here is a proof using generating functions. Let $c\geq 2$ and $k\geq 2$ be fixed.
Let $X=(X_1(n),\ldots,X_k(n))$ be the $k$-tuple of occupancy numbers at time $n$, i.e. $X_i(n)$ = number of bins of ty …
7
votes
Accepted
A sum of two binomial random variables
Here is a (surprising) proof using Cauchy-Schwarz and "rearrangement".
The following lemma will be the key.
Lemma
: Let $X,Y$ be independent integer-valued rvs, then \begin{align*}
(a)\; &\mbox{ for …
5
votes
Accepted
Expected number of compositions needed to get constant function
This question was completely settled by J.A. Fill here:
https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.8.641
3
votes
Accepted
Bounding the max-loaded bin using${m \choose k} \|A\|_k^k$
The following inequality holds:
$$\mathbb{P}(C_k(m)\geq 1)\geq \mathbb{P}(\mathrm{Bin}(m, \lVert A\rVert_k)\geq k)$$
where here and in the sequel $\mathrm{Bin}(n,p)$ denotes a binomially distributed r …
0
votes
Coupon collector targeting a collection among many
There a well known generating function methods (the ''symbolic method'' and ''Poissonization'') which can be used to deal with this kind of question.
However, I am unable to point to a reference for …