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• 03:02, 5 June 2024 Etone talk contribs created page 组合数学 (Fall 2024)/Matching theory (Created page with "== Systems of Distinct Representatives (SDR)== A '''system of distinct representatives (SDR)''' (also called a '''transversal''') for a sequence of (not necessarily distinct) sets <math>S_1,S_2,\ldots,S_m</math> is a sequence of <font color=red>''distinct''</font> elements <math>x_1,x_2,\ldots,x_m</math> such that <math>x_i\in S_i</math> for all <math>i=1,2,\ldots,m</math>. === Hall's marriage theorem === If the sets <math>S_1,S_2,\ldots,S_m</math> have a system of dist...")
• 12:14, 29 May 2024 Etone talk contribs created page 组合数学 (Fall 2024)/Ramsey theory (Created page with "== Ramsey's Theorem == === Ramsey's theorem for graph === {{Theorem|Ramsey's Theorem| :Let <math>k,\ell</math> be positive integers. Then there exists an integer <math>R(k,\ell)</math> satisfying: :If <math>n\ge R(k,\ell)</math>, for any coloring of edges of <math>K_n</math> with two colors red and blue, there exists a red <math>K_k</math> or a blue <math>K_\ell</math>. }} {{Proof| We show that <math>R(k,\ell)</math> is finite by induction on <math>k+\ell</math>. For the...")
• 01:33, 28 May 2024 Etone talk contribs created page 概率论与数理统计 (Spring 2024)/Entropy and volume of Hamming balls (Created page with "在求解抛掷公平硬币（fair coin）的尾概率时，我们经常会需要分析如下二项式系数求和： :<math>\sum_{k=0}^r{n\choose k}</math>，对于某个<math>1\le r\le n</math> 这其实等价与求一个 <math>n</math> 维汉明空间中半径为 <math>r</math> 的球的体积。 :{|border="2" width="100%" cellspacing="4" cellpadding="3" rules="all" style="margin:1em 1em 1em 0; border:solid 1px #AAAAAA; border-collapse:collapse;empty-cells:show;" | :'...")
• 02:59, 26 May 2024 Etone talk contribs created page 概率论与数理统计 (Spring 2024)/OST and applications (Created page with "=可选停时定理 (OST)= '''可选停时定理''' ('''Optional Stopping Theorem''', '''OST''')，有事也被称为'''鞅停时定理''' ('''Martingale Stopping Theorem''')、'''可选抽样定理''' ('''Optional Sampling Theorem''') 等，是约瑟夫·杜布 ([https://en.wikipedia.org/wiki/Joseph_L._Doob Joseph Doob]) 发现的关于鞅的停时的刻画定理。 首先定义鞅 (martingale)。这是一类由公平赌博定义的随机过程。 {{Theorem|定义（...")
• 02:59, 26 May 2024 Etone talk contribs created page 概率论与数理统计 (Spring 2024)/Hoeffding's lemma (Created page with "霍夫丁引理（Hoeffding's lemma）在霍夫丁不等式（[https://en.wikipedia.org/wiki/Hoeffding%27s_inequality Hoeffding's inequality]）的证明中，扮演着关键角色。该引理陈述如下： {{Theorem|霍夫丁引理| :若随机变量 <math>Y</math> 满足 <math>\mathbb{E}[Y]=0</math> 且存在实数 <math>a,b\in\mathbb{R}</math> 使得几乎必然地 (a.s.) <math>a\le Y\le b</math>，则对于任意 <math>\lambda\in\mathbb{R}</math>，都有 ::<math>\ma...")
• 09:48, 20 May 2024 Etone talk contribs created page 组合数学 (Fall 2024)/Extremal set theory (Created page with "== Sunflowers == An set system is a '''sunflower''' if all its member sets intersect at the same set of elements. {{Theorem|Definition (sunflower)| : A set family <math>\mathcal{F}\subseteq 2^X</math> is a '''sunflower''' of size <math>r</math> with a '''core''' <math>C\subseteq X</math> if ::<math>\forall S,T\in\mathcal{F}</math> that <math>S\neq T</math>, <math>S\cap T=C</math>. }} Note that we do not require the core to be nonempty, thus a family of disjoint sets is...")