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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 …
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7 votes
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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 …
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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} …
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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 …
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2 votes
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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 $n\geq s$. …
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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 $ …
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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 $ …
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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. …
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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 …
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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 …
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3 votes
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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 …
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7 votes
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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 …
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5 votes
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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
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3 votes
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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 …
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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 …
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