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The study of probability distributions over graphs. For example, the Erdős–Rényi model where each edge occurs independently with equal probability.
7
votes
Accepted
Threshold for appearance of a cycle
In this case, assuming $c\lt 1$ is independent of $n$, the number of cycles is asymptotically Poisson with constant mean $f(c)$. So asymptotically there is a constant nonzero probability $e^{-f(c)}$ t …
3
votes
how rare random bipartite graphs in all random regular graphs
Take $2n$ vertices. Regular bipartite graphs have $n$ vertices of each colour, and most have only one colouring because they are connected (for degree $\ge 3$). So take the asymptotic number of regul …
6
votes
Random planar, bipartite graphs
First make a "random" quadrangulation, then take a random subgraph of that. Since every planar bipartite graph can be made into a quadrangulation by adding edges, at least you know that every outcome …
5
votes
Accepted
Cut-distance between two Erdos-Renyi random graphs
(To answer Anthony, I'm taking the two graphs to be on the same vertex set.)
This is an argument, without details, that the answer is $\Omega(n^{3/2})$.
Generate the graphs two vertices at a time. A …
12
votes
Accepted
What is the chromatic number of the Erdős–Rényi graph G(n,d/n) when d < 1?
Consider subgraphs consisting of two cycles with an edge in common (i.e. a theta-graph or something more complex). The number of such labelled graphs with $t$ vertices is at most $n^t$, and the probab …
3
votes
expected length of a largest cycle in regular graph
I'm not going to do this calculation, but here is how it can be done. Any interval which contains the length of the longest cycle with probability tending to 1 will also contain the length of the long …
6
votes
Accepted
Length of longest directed circuit in random tournament
A random tournament is strongly connected with probability tending to 1 exponentially fast, and all strongly connected tournaments have hamiltonian cycles.
3
votes
Accepted
matchings in hypergraphs
I'm assuming that the degree of a vertex is the number of edges incident with it (other definitions are possible). The degree of a vertex in $G_k(n,p)$ has a binomial distribution
$$\operatorname{Bin} …
6
votes
Comparing two measures on trees on $n$ vertices
It's a nice question that I don't know a complete answer to. However it can be seen that the measures are not exactly the same. Take $p$ to be very small. The most likely connected $G$ is a tree, a …
0
votes
Model for random graphs where clique number remains bounded
Divide the vertex set into a fixed number of parts, in any way you like (such as randomly). Choose two probabilities $p_1,p_2$, where $p_1\le n^{-\varepsilon}$ for some fixed $\varepsilon\gt 0$ and $p …
3
votes
Accepted
Unique maximum degree in tournament
I can't find a published proof of this known result, but here is a close miss.
In this paper, page 256, is a short proof that a random undirected graph has a unique vertex of maximum degree almost su …
2
votes
When is a large graph with a given degree sequence likely to be connected?
Second edition
This is a partial answer to the question per the "Clarification Update", but first I'll generalize a little. Suppose that for each $n$ we have a degree sequence $n_0,n_1,n_2,\ldots$, …
9
votes
Selection of an n-vertex graph at random
There is a very efficient method.
See Nicholas C. Wormald Generating Random Unlabelled Graphs
1
vote
Generate random graphs that satisfy the triangle inequality
Make an intermediate graph $H$ with arbitrary random nonnegative edge lengths. Now define a graph $G$ with the same edges, with the length of each edge $vw$ in $G$ being the distance between $v$ and $ …
5
votes
Uniform sampling of random connected graph with given number of vertices/edges
I don't know if this has been programmed. I'll describe one method based on counting. Let $c_{n,m}$ be the number of labelled connected graphs with $n$ vertices and $m$ edges.
Choose a pair of dist …