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29 May 2024
- 12:3312:33, 29 May 2024 diff hist +1,308 组合数学 (Spring 2024) →Concepts
- 12:1412:14, 29 May 2024 diff hist +26,029 N 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..." current
- 12:1412:14, 29 May 2024 diff hist −1 组合数学 (Spring 2024) →Lecture Notes
- 12:1412:14, 29 May 2024 diff hist +138 组合数学 (Spring 2024) →Lecture Notes
- 12:1312:13, 29 May 2024 diff hist −1 组合数学 (Spring 2024) →Lecture Notes
28 May 2024
- 01:3301:33, 28 May 2024 diff hist +6,589 N 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;" | :'..." current
- 01:3201:32, 28 May 2024 diff hist +118 概率论与数理统计 (Spring 2024) →Lectures
26 May 2024
- 02:5902:59, 26 May 2024 diff hist +18,855 N 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(..." current
- 02:5902:59, 26 May 2024 diff hist +4,639 N 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..." current
- 02:5802:58, 26 May 2024 diff hist +576 概率论与数理统计 (Spring 2024) →Lectures
20 May 2024
- 09:4909:49, 20 May 2024 diff hist +1,218 组合数学 (Spring 2024) →Concepts
- 09:4809:48, 20 May 2024 diff hist +51,460 N 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..." current
- 09:4809:48, 20 May 2024 diff hist +474 组合数学 (Spring 2024) →Lecture Notes
19 May 2024
- 13:5713:57, 19 May 2024 diff hist 0 概率论与数理统计 (Spring 2024) →Lectures
- 13:5613:56, 19 May 2024 diff hist +3,071 概率论与数理统计 (Spring 2024) →Concepts
- 13:5513:55, 19 May 2024 diff hist +153 概率论与数理统计 (Spring 2024) →Lectures
14 May 2024
- 09:3809:38, 14 May 2024 diff hist +18,939 N 组合数学 (Fall 2024)/Extremal graph theory Created page with "== Forbidden Cliques == Extremal graph theory studies the problems like "how many edges that a graph <math>G</math> can have, if <math>G</math> has some property?" === Mantel's theorem === We consider a typical extremal problem for graphs: the largest possible number of edges of '''triangle-free''' graphs, i.e. graphs contains no <math>K_3</math>. {{Theorem|Theorem (Mantel 1907)| :Suppose <math>G(V,E)</math> is graph on <math>n</math> vertice without triangles. Then <m..." current
- 09:3809:38, 14 May 2024 diff hist +158 组合数学 (Spring 2024) →Lecture Notes
30 April 2024
- 13:3613:36, 30 April 2024 diff hist +1 概率论与数理统计 (Spring 2024) →Concepts
- 13:3513:35, 30 April 2024 diff hist +64 概率论与数理统计 (Spring 2024) →Concepts
- 13:3413:34, 30 April 2024 diff hist +1,032 概率论与数理统计 (Spring 2024) →Concepts
- 13:3113:31, 30 April 2024 diff hist +268 概率论与数理统计 (Spring 2024) →Lectures
24 April 2024
- 03:0203:02, 24 April 2024 diff hist +1,091 组合数学 (Spring 2024) →Concepts
- 02:5702:57, 24 April 2024 diff hist +27,151 N 组合数学 (Fall 2024)/The probabilistic method Created page with "== The Probabilistic Method == The probabilistic method provides another way of proving the existence of objects: instead of explicitly constructing an object, we define a probability space of objects in which the probability is positive that a randomly selected object has the required property. The basic principle of the probabilistic method is very simple, and can be stated in intuitive ways: *If an object chosen randomly from a universe satisfies a property with posi..." current
- 02:5702:57, 24 April 2024 diff hist +157 组合数学 (Spring 2024) →Lecture Notes
22 April 2024
- 03:1403:14, 22 April 2024 diff hist +5,139 N 概率论与数理统计 (Spring 2024)/Weierstrass Approximation Theorem Created page with "[https://en.wikipedia.org/wiki/Stone%E2%80%93Weierstrass_theorem '''魏尔施特拉斯逼近定理''']('''Weierstrass approximation theorem''')陈述了这样一个事实:闭区间上的连续函数总可以用多项式一致逼近。 {{Theorem|魏尔施特拉斯逼近定理| :设 <math>f:[a,b]\to\mathbb{R}</math> 为定义在实数区间 <math>[a,b]</math> 上的连续实值函数。对每个 <math>\epsilon>0</math>,存在一个多项式 <math>p</math> 使得对..." current
- 03:1303:13, 22 April 2024 diff hist +7,005 N 概率论与数理统计 (Spring 2024)/Threshold of k-clique in random graph Created page with "在 Erdős-Rényi 随机图模型 <math>G(n,p)</math> 中,一个随机无向图 <math>G</math> 以如下的方式生成:图 <math>G</math> 包含 <math>n</math> 个顶点,每一对顶点之间都独立同地以概率 <math>p</math> 连一条无向边。如此生成的随机图记为 <math>G\sim G(n,p)</math>。 固定整数 <math>k\ge 3</math>,考虑随机图 <math>G\sim G(n,p)</math> 包含 <math>K_k</math>(<math>k</math>-团,<math>k</math>-clique)子图..." current
- 03:1203:12, 22 April 2024 diff hist +8,968 N 概率论与数理统计 (Spring 2024)/Two-point sampling Created page with "= 利用线性同余方程构造两两独立的随机变量 = 令<math>p</math>为一质数。考虑模<math>p</math>余数构成的集合<math>[p]=\{0,1,\ldots,p-1\}=\mathbb{Z}_p</math>。众所周知,当<math>p</math>为质数时,<math>\mathbb{Z}_p</math>为对模<math>p</math>加法和乘法运算闭合的'''有限域'''。 我们现在构造一系列值域为<math>[p]</math>的'''两两独立'''('''pairwise Independent''')且'''均匀分布'''('''uniforml..." current
- 03:1203:12, 22 April 2024 diff hist +325 概率论与数理统计 (Spring 2024) →Lectures
15 April 2024
- 14:5814:58, 15 April 2024 diff hist +750 概率论与数理统计 (Spring 2024) →Concepts
- 14:5714:57, 15 April 2024 diff hist +155 概率论与数理统计 (Spring 2024) →Lectures
- 14:5514:55, 15 April 2024 diff hist 0 概率论与数理统计 (Spring 2024) →Lectures
- 14:5414:54, 15 April 2024 diff hist +189 概率论与数理统计 (Spring 2024) →Lectures
12 April 2024
- 09:0209:02, 12 April 2024 diff hist −1 组合数学 (Spring 2024) →Lecture Notes
- 09:0109:01, 12 April 2024 diff hist +186 组合数学 (Spring 2024) →Lecture Notes
9 April 2024
- 13:2713:27, 9 April 2024 diff hist +14,440 N 组合数学 (Fall 2024)/Existence problems Created page with "== Existence by Counting == === Shannon's circuit lower bound=== This is a fundamental problem in in Computer Science. A '''boolean function''' is a function in the form <math>f:\{0,1\}^n\rightarrow \{0,1\}</math>. [http://en.wikipedia.org/wiki/Boolean_circuit Boolean circuit] is a mathematical model of computation. Formally, a boolean circuit is a directed acyclic graph. Nodes with indegree zero are input nodes, labeled <math>x_1, x_2, \ldots , x_n</math>. A circuit h..." current
- 13:2613:26, 9 April 2024 diff hist +17,231 N 组合数学 (Fall 2024)/Cayley's formula Created page with "== Cayley's Formula == We now present a theorem of the number of labeled trees on a fixed number of vertices. It is due to [http://en.wikipedia.org/wiki/Arthur_Cayley Cayley] in 1889. The theorem is often referred by the name [http://en.wikipedia.org/wiki/Cayley's_formula Cayley's formula]. {{Theorem|Cayley's formula for trees| : There are <math>n^{n-2}</math> different trees on <math>n</math> distinct vertices. }} The theorem has several proofs, including the bijectio..." current
- 13:2613:26, 9 April 2024 diff hist +87 组合数学 (Spring 2024) →Lecture Notes
- 13:2413:24, 9 April 2024 diff hist +80 组合数学 (Spring 2024) →Lecture Notes
8 April 2024
- 08:4208:42, 8 April 2024 diff hist +985 概率论与数理统计 (Spring 2024) →Concepts
- 08:4108:41, 8 April 2024 diff hist +11,838 N 概率论与数理统计 (Spring 2024)/Average-case analysis of QuickSort Created page with "[http://en.wikipedia.org/wiki/Quicksort '''快速排序'''('''Quicksort''')]是由Tony Hoare发现的排序算法。该算法的伪代码描述如下(为方便起见,假设数组元素互不相同——更一般情况的分析易推广得到): '''''QSort'''''(A): 输入A[1...n]是存有n个不同数字的数组 if n>1 then '''pivot''' = A[1]; 将A中<pivot的元素存于数组L,将A中>pivot的元素存于数组R; \\保持内部元素之..." current
- 08:4008:40, 8 April 2024 diff hist +126 概率论与数理统计 (Spring 2024) →Lectures
27 March 2024
- 04:3704:37, 27 March 2024 diff hist +78 组合数学 (Spring 2024) →Concepts
- 04:3604:36, 27 March 2024 diff hist +79 组合数学 (Spring 2024) →Concepts
- 04:3504:35, 27 March 2024 diff hist +274 组合数学 (Spring 2024) →Concepts
- 04:2804:28, 27 March 2024 diff hist +1,749 组合数学 (Spring 2024) →Concepts
- 04:2704:27, 27 March 2024 diff hist +19,696 N 组合数学 (Fall 2024)/Pólya's theory of counting Created page with "== Groups == A group <math>(G,\cdot)</math> is set <math>G</math> along with a binary operator <math>\cdot</math> which satisfies the following axioms: * ''closure'': <math>\forall g,h\in G, g\cdot h \in G</math>; * ''associativity'': <math>\forall f,g,h\in G, f\cdot(g\cdot h)=(f\cdot g)\cdot h</math>; * ''identity'': there exists a special element <math>e\in G</math>, called the '''identity''', such that <math>e\cdot g=g</math> for any <math>g\in G</math>; * ''inverse''..." current
- 04:2604:26, 27 March 2024 diff hist +105 组合数学 (Spring 2024) →Lecture Notes
26 March 2024
- 18:5518:55, 26 March 2024 diff hist +57 组合数学 (Spring 2024) →Lecture Notes
25 March 2024
- 09:5909:59, 25 March 2024 diff hist +2,781 概率论与数理统计 (Spring 2024) →Concepts