Questions tagged [random-graphs]
The study of probability distributions over graphs. For example, the Erdős–Rényi model where each edge occurs independently with equal probability.
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Another betweenness centrality measure: neighbourhood centrality
Among the many centrality measures that I have heard of, I miss the following (but maybe I'm just blind).
Consider a graph $G$ with $k$ connected components $G_i$ of size $|G_i|$. The number of node ...
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38 views
Cycle statistics of random endomorphism
Let $S$ be a set with $n$ elements and let $f:S\to S$ be a random function, chosen uniformly among the $n^n$ possibilities. Considering $f$ as a directed graph of constant outdegree $1$, i. e. with ...
2
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1answer
90 views
Probabilistic bound to the number of edge disjoint triangles in a random graph
Let $G$ be a random graph with $n$ vertices, and let $\delta(G)$ be the maximum number of triangles in $G$.
Question. How to prove the bound $$P(\delta(G)) \leq m - t \sqrt{f(m)}) \leq 2e^{-t^2 / 4}$...
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1answer
576 views
What is the theory of the random poset?
$\DeclareMathOperator\Th{Th}$The random poset is the Fraisse limit of the class of finite posets, just like the random graph is the Fraisse limit of the class of finite graphs? That is, the random ...
2
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1answer
113 views
Random graphs and Benjamini-Schramm convergence
I am looking for literature on the question whether a randomly chosen sequence of $k$-regular graphs converges in the Benjamini-Schramm sense to the universal covering with probability one.
There are ...
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3answers
176 views
Random graphs defined by a set of tiles
Related to this question, which I asked at MSE, I'd like to ask this one here:
Consider a (large) graph $G$ and its multi-set of tiles $T$, i.e. the multi-set of its vertex-induced subgraphs, i.e. the ...
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30 views
Eigenvalue bounds of a random graph with a clique
I'm looking into this paper and having some problems proving (ii) of proposition 2.1. I don't quite understand how the lemma is proved. I also read the original paper where the lemma comes from but ...
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3answers
297 views
How to show that random graphs cannot be embedded with short edges
For each (not necessarily planar) embedding of a graph in $\mathbb{R}^k$ one can calculate the ratio
$$\gamma = \frac{\textsf{mean Euclidean length of edges}}{\textsf{mean Euclidean distance between ...
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2answers
105 views
How to define probability over graphs?
How can one formally define a random graph variable?
If G is a random graph variable, then any finite graph is a realization of G. Formally a r.v maps the set of outcomes to a measurable space (may be ...
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Random graphs with prescibed degrees and triangles
In short: a random graph model generates (multi-)graphs with prescribed number of edges and minimal number of triangles for each vertex. Questions arise about the actual number of triangles and the ...
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0answers
89 views
Generating a random graph with bounds on degree and diameter
What would be a way to generate a random simple graph with diameter lesser than a given number, and in which there are given lower and upper bounds (bounds being uniform across vertices) on the degree ...
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47 views
Are two degree sequences compatible, for random simple graph generation?
Consider a set $V$ of $n$ vertices, and three degree sequences $a_i$, $b_i$ and $c_i$ such that $c_i = a_i+b_i$, $i=1..n$.
Assume these degree sequences are graphical: there exist simple graphs (no ...
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136 views
Does the random graph interpret the random directed graph?
The random graph is the Fraisse limit of the class of finite graphs, the random directed graph is the Fraisse limit of the class of directed graphs, a directed graph is just a set with a binary ...
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3answers
276 views
Simple graphs with prescribed degrees as disjoint union of simple subgraphs with prescribed degrees
Consider a set $V$ of $n$ vertices, and three degree sequences $a_i$, $b_i$ and $c_i$ such that $c_i = a_i+b_i$, $i=1..n$.
Assume these degree sequences are graphical: there exist simple graphs (no ...
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4answers
837 views
What nodes of a graph should be vaccinated first?
Consider a graph, choose some "p: 0<p<1" (probability to infect the neighbor node).
Choose some random number "K" of nodes which are "infected" initially.
So we ...
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1answer
197 views
Random subgraph properties
Consider a graph $G$ of $N$ vertices and $M$ edges, and assume $G$ has typical complex network properties: it is not necessarily connected, but it has a high clustering coefficient and a giant ...
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160 views
Is there are good algebraic model of random n-hypergraphs?
Suppose $F$ is a finite field and $-1$ is a square in $F$. Let $E$ be the binary relation on $F$ where $(a,b) \in E$ iff $a - b$ is a square. Then $(F,E)$ is called a Paley graph. Paley graphs are ...
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212 views
Triangle coloring in random graph
Given $m$ persons (men and women) and $n$ balls, each person randomly selects $3$ balls. Once all of them complete the selection process, we color the balls with $2$ colors, white and black, such that ...
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1answer
62 views
Sources of information on algorithms for finding Hamiltonian cycles (Pósa)
I research various algorithms in complex networks and I am quite new in this field. I am currently focusing on random geometric graphs - Pósa's algorithm for finding a hamiltonian cycle. Can you ...
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105 views
Additional examples of classes of networks whose Hasse diagram of the poset is a perfect graph
This question is very important for my research, which is why I ask it here.
I do not have a formal background in graph theory so please excuse me if I state a term incorrectly (and feel free to ...
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0answers
103 views
Expansion of random subgraphs of a bi-regular bipartite graph
Let $G = (L, R, E)$ be a bi-regular bipartite graph, with $|L|=n$ and $|R| = C \cdot n$, where $C$ is a large constant. Let $d$ be its (constant) right-degree.
We know $G$ is a good spectral expander. ...
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1answer
83 views
making a random uniform hypergraph linear
Let $\mathcal{H}_{n,p,h}=(V,E)$ be a random $h$-uniform hypergraph on $[n]$, sampled according to the usual binomial distribution. We known that with high probability, the number of edges in $\mathcal{...
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1answer
183 views
Structures for random graphs with structure
Background[You may skip this and go immediately to the Definitions.]
Crucial features of a (random) graph or network are:
the degree distribution $p(d)$ (exponential, Poisson, or power law)
the mean ...
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1answer
68 views
Hyper-degree sequences: How to count them and how to construct hyper-graphs from them?
From an answer to this question I have learned how to ask this question properly.
Consider a $k$-uniform hypergraph on $n$ nodes, i.e. a family of $k$-subsets of $[n]= \{1,2,\dots,n\}$ (the hyperedges)...
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0answers
129 views
Two kinds of generating functions
Sorry for a possibly off-the-topic question, but I am afraid to gain the necessary overview to give an answer (supposed the question is not ill-posed) is beyond my capabilities.
In the course of ...
3
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1answer
85 views
Degree sequences after vertex removals
Consider a graph $G=(V, E)$ with $|V|=n$ vertices. Let $(v_1, \dots, v_n)$ be an ordered list of its vertices. Let $G_i=G[\{v_{i+1}, \dots, v_n\}]$ be the induced subgraph on the last $n-i$ vertices. ...
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3answers
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Issue UPDATE: in graph theory, different definitions of edge crossing numbers - impact on applications?
QUICK FINAL UPDATE: Just wanted to thank you MO users for all your support. Special thanks for the fast answers, I've accepted first one, appreciated the clarity it gave me. I've updated my torus ...
3
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1answer
116 views
Reference request - random regular graphs vs random graphs w/ degree sequence
There are some properties that are easily studied for random d-regular graphs, but that are very hard to extend to random graphs with a given degree sequence (e.g. whether a graph is w.h.p. ...
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2answers
99 views
Fast uniform generation of random graphs with given degree sequences - any implementation?
The paper below presents a linear-time algorithm for uniform generation of random graphs with given degree sequences [1].
This is very interesting in practice, but I found no implementation. However, ...
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0answers
95 views
The diameter of random regular graphs
In 1982, B. Bollobas and Vega in the paper gave the configurational model to generate $r$-regular random graphs. They gave the following theorem (Theorem 1 in the paper).
Theorem: Let $r\geq 3$ and $\...
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1answer
72 views
Relation between random graph models $G^{(B)}_{n,m}$ and $G_{n,m}$
In Frieze, Alan; Karoński, Michał, Introduction to random graphs, in Section 1.3 Pseudo-Graphs, there is a model of random multi-graphs, which is denoted as $\mathbb{G}^{(B)}_{n,m}$.
Def. A random ...
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1answer
103 views
Probability in Chromatic number upper bound of induced subgraph
Let $G=(V, E)$ be a graph with chromatic number $\chi(G)=1000 .$ Let $U \subset V$ be a random subset of $V$ chosen uniformly from among all $2^{|V|}$ subsets of $V$. Let $H=G[U]$ be the induced ...
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1answer
110 views
Survey/references on random geometric $K$-NN – $K$-nearest-neighbour graphs?
[Edit:] Some related info on number of connected components of NN-graphs can be found here: https://cstheory.stackexchange.com/a/47037/2408
Sample $N$ points in $\mathbb{R}^d$ from some distribution $...
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1answer
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Ensemble averaging in a random graph (or network) in the large $N$ limit [closed]
I have a random graph/network described by the adjacency matrix $(a_{ij})_{N\times N}$ where $a_{ij}=1$ with probability $p$. Each node in the graph is associated with a continuous quantity $\eta_i=\...
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51 views
Average number of edges of an induced graph by using the edge-based node selection technique on a graph with arbitrary degree distribution
Let $G(U,V,E)$ be a simple, undirected, bipartite graph and $U=\{u_1,u_2,{\cdots},u_n\}$ and $V=\{ v_{1},v_{2},\cdots,v_{n}\}$. Let $d_k^l$ be the number of vertex with degree $k$ in $l$, where $l \in ...
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1answer
195 views
Critical probability for Erdos-Renyi digraphs to be strongly connected
Given $p \in [0,1]$, an Erdos-Renyi graph ${ER}(n,p)$ on $n$ vertices is constructed by defining, for each unordered couple of distinct vertices ${i,j}$ an edge between $i$ and $j$ with probability $p$...
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214 views
Probability that a random multigraph is simple
Question.
Consider a given sequence of $n$ integers $d_1$, $d_2$, $\cdots$, $d_n$ with $\sum_i d_i$ even and $d_i\le n$ for all $i$. One may sample a random multi-graph having this degree sequence ...
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1answer
316 views
Graph with path of length $\geq n$ along grid diagonals - a known result in graph theory?
Is the following lemma a well known result in graph theory?
I am studying a basic existence result that appears to be simple yet powerful. I have not seen it stated as an important result in graph ...
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1answer
95 views
Relation between expected values of eigenvalues of Laplacian matrix of a graph and eigenvalues of expected Laplacian matrix of that graph?
Particularly, I am dealing with Erdős–Rényi random 𝐺(𝑛,𝑝), so the expected Laplacian matrix of 𝐺(𝑛,𝑝) is 𝑝(𝐽𝑛−𝐼𝑛), where 𝐽𝑛 and 𝐼𝑛 are one and identity matrices, respectively.
In ...
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0answers
55 views
Count shortest path with different lengths in random graph
Let $G(n,p)$ be an Erdos-Renyi random graph on $n$ vertices with probability $p$, i.e. for each pair of vertices, they are connected directly by an undirected edge with probability $p$. Suppose we are ...
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1answer
60 views
An attempt to find expected value of clique number of special random graph
Let $G(n)=(V,\mathcal{E})$ be a random graph definded as follows:
$V=[n]=\{1,2, ... ,n\}$ and for all $i,j\in V$ so that $i\ne j$ we have $\{i,j\}\in\mathcal{E}$ with probability $p$. Where $p\in[0,1]...
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4-cycles vs eigenvalue information on quasi-random graphs
My (philosophical) question arises from reading the wonderful paper of Chung-Graham-Wilson where the authors introduces the notion of quasi-random graphs.
The main purpose of the paper is to show ...
12
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1answer
392 views
Distribution of degree in graphs: when is the friendship paradox the paradox it wants to be?
$\DeclareMathOperator\deg{deg}\DeclareMathOperator\ndeg{ndeg}\newcommand\abs[1]{\lvert#1\rvert}$The friendship paradox goes most people have fewer friends than their friends have on average. The ...
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1answer
100 views
Attacking a network at minimum cost
A target system is modelled as a giant, undirected, simple graph $G$ (simple meaning no hyperedge) that can be scrutinized in adequate detail to budget and plan the attack: its topology changes slowly ...
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1answer
204 views
Asymptotically tight concentration of norms of subgaussian random vectors with independent coordinates, as the dimension $n \to \infty?$
Let $X=(X_1 \dots X_n)\in \mathbb{R}^n,$ be a subgaussian random vector so that $X_i$'s are independent, $\mathbb{E}X_i = 0, \mathbb{E}X_i^2=1.$ Before we pose our question, let's state the following:
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0answers
61 views
Expected number of bridges in a random subgraph
I am researching connectivity in random subgraphs and have come across the following problem.
A bridge between two vertices $a$ and $b$ of a graph $G$ is an edge $e$ such that removing $e$ from $G$ ...
3
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1answer
116 views
Unique maximum degree in tournament
Consider a uniform random tournament with $n$ vertices. (Between any two vertices $x,y$, with probability $0.5$ draw an edge from $x$ to $y$; otherwise draw an edge from $y$ to $x$.) Let $p(n)$ denote ...
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1answer
108 views
Size of minimum cut in random graph
Consider a uniform random tournament with $n$ vertices. (Between any two vertices $x,y$, with probability $0.5$ draw an edge from $x$ to $y$; otherwise draw an edge from $y$ to $x$.) The score of each ...
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2answers
106 views
Difference between two largest degrees
Consider a uniform random tournament with $n$ vertices. (Between any two vertices $x,y$, with probability $0.5$ draw an edge from $x$ to $y$; otherwise draw an edge from $y$ to $x$.) Let $S$ be the ...
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1answer
83 views
Limit of normalized sum of Dirac measures at first $\lfloor p/2\rfloor$ eigenvalues of the sample covariance matrix, with Marcenko-Pastur assumptions?
Let $\lfloor{*}\rfloor$ denotes the nearest integer $\le *$. I'm asking myself the question what's the limit of the part of the empirical spectral distribution corresponding to the first $\lfloor{p/2}...
