**-1**

votes

**0**answers

9 views

### Expected number of tree component should be less than equal to zero in random graph

In Erdos-Renyi random graph $G(n,p(n))$, set $p(n) ≥ (\frac{\ln n}{10n})$. We want to show that expected number of tree component on 11 vertices with this probability $p(n) ≥ (\frac{\ln n}{10n})$ ...

**15**

votes

**11**answers

2k views

### Chromatic number of graphs of tangent closed balls

The Koebe–Andreev–Thurston theorem gives a characterization of planar graphs in terms of disjoint circles being tangent. For every planar graph $G$ there is a disk packing whose graph is $G$. What ...

**1**

vote

**1**answer

70 views

### Counting bounded genus non-isomorphic graphs

What is the number of non-isomorphic $2n$ vertex balanced bipartite graphs of degree at most $d$ and genus $g$?
I am most interested in $d\leq3$ and $g=0$.

**0**

votes

**1**answer

266 views

### Reverse optimization of a minimum cost flow network

Given an undirected graph $(V,E)$, with $W$ as the weight of each edge, and a convex cost function $F(X)$, such as $|X|^k$ ($k>1$).
The cost to send $x$ unit of flow through edge $e_i$ is defined ...

**4**

votes

**3**answers

175 views

### Relation between diametral path and regularity of a graph

Let $G(V,E)$ be a graph. A path whose length is equal to the diameter of a graph is called a diametral path. In a cycle graph every vertex has $2$ diametral paths. Now I need to prove that this:
...

**0**

votes

**0**answers

44 views

### Zero-one law in binomial random graph model $G(n,p)$

Consider the binomial random graph model $G(n,p)$ with $0<p<1$. We say that $G(n,p)$ satisfies the Zero-One law if for every first order property $Q$ one has $\lim\limits_{n \rightarrow \infty} ...

**0**

votes

**0**answers

35 views

### Reconstructing a graph from set of sequences of edges

I have the following problem to solve: Given a set of sequences of edges of an undirected, planar, connected graph, find a "reasonable" reconstruction of the graph. There is an unknown number of ...

**-5**

votes

**0**answers

66 views

### Can any polynomial expressed as a chromatic polynomial? [on hold]

Is it possible any polynomial with integer coefficients to be (or converted to) a chromatic polynomial that corresponds to a graph?

**6**

votes

**2**answers

316 views

### Can every permutation group be realized as the automorphism group of a graph (acting on a subset of the vertices)?

By Frucht's theorem, every finite group can be realized as the automorphism group of a finite undirected graph. Because a permutation group is a finite group, it is clear that every permutation group ...

**11**

votes

**1**answer

952 views

### Menger's theorem via matroids

Let $G=(V,E)$ be an oriented graph, $Y\subset V$ be some fixed set of its vertices. Call $A\subset V$ independent if there exist $|A|$ vertex-disjoint paths starting in $A$ and ending in $Y$. It is ...

**0**

votes

**0**answers

14 views

### is any closed form relation that can state the error probability of code versus its variable and check node degree distributions?

In Low Density parity check code design, when bit (or frame) error probability of code is the objective of the design, we need a closed form relation between error probably (or even an approximate or ...

**4**

votes

**1**answer

454 views

### inequality with exponents

We are given a graph $G$, each vertex $v$ has an assigned value $\gamma_v\in [0,1]$, and it happens that for every $v$ we have $\gamma_v+\sum_{u\in \delta(v)} \gamma_u = 1$. Assume that $\sum_v ...

**0**

votes

**0**answers

51 views

### Binary operations on graphs

Are there "binary operations" on graphs like in (https://en.wikipedia.org/wiki/Graph_product), which make the set of all graphs ("under consideration")
a (abelian) group or
a (commutative) ring or
a ...

**2**

votes

**3**answers

182 views

### Existence of special graph

Let $G$ be a $n$-vertices graph and $\lambda_1$ is the largest eigenvalue of this graph. If $\lambda_1$ is an integer value, we can easily find the $\lambda_1$- regular graph with $n$ vertices. Now, ...

**0**

votes

**1**answer

54 views

### Choosing directed subgraph in a triangulation

Consider triangulation $T.$
Is it always possible to choose such a subgraph $H$ of $T$ that has a common edge with every face of $T$ and can be directed in such way that indegrees of all vertices of ...

**0**

votes

**0**answers

36 views

### Limit probability of a complete bipartite random graph $G(n,n,p)$ is connected [on hold]

I need to calculate the following probability limit for a complete bipartite random graph $G(n,n,p)$ in the Erdos-Renyi model:
\begin{equation}
\lim_{n\rightarrow\infty}\mathbb{P}[G(n,n,p) \text{ is ...

**1**

vote

**1**answer

142 views

### Finding many disjoint sub-trees with many leaves

Let $T$ be a rooted binary tree with $L$ leaves, and let $\ell$ be a natural number smaller than $L$. The question is what is the maximal number of disjoint rooted sub-trees with at least $\ell$ ...

**-4**

votes

**0**answers

37 views

### Are Undirected Edges and Directed Edges disjoint sets? [closed]

Many graph processing and storage frameworks assume that, in their graphs, all edges are directed. There are no edge whose type is undirected under the hood. There is only an interpretation, when ...

**2**

votes

**1**answer

32 views

### Edge-disjoint paths avoiding some subgraphs

Let $G$ be a directed graph on $n$ vertices. Let $H_1$, ..., $H_k$ be marked subgraphs of $G$. (Specifically, each $H_i$ consists of a subset of the vertices of $G$ and a subset of the edges of the ...

**2**

votes

**0**answers

54 views

### Number of $(2n-1)$-edge-colorings of the complete graph $K_{2n}$

I just started reading about graph theory and have a question (which might be trivial). How many $(2n-1)$ edge colorings of $K_{2n}$ are there?
A vaguer question: can I write $K_{4n}= K_4 + K_4 ...

**-1**

votes

**0**answers

49 views

### Central limit theorem for perfect matching counts [closed]

This is a modification to one of my questions:
Set $N_G$ the number of copies of graph $G$ in the Erdős–Rényi random graph model $G(n,p)$. We have the law of large number for the number of copies of ...

**4**

votes

**2**answers

245 views

### Are all numbers from $1$ to $n!$ the number of perfect matchings of some bipartite graph?

Let $f(G)$ give the number of perfect matchings of a graph $G$.
Consider set $\mathcal N_{2n}=\{0,1,2,\dots,n!-1,n!\}$.
Consider collection of all $2n$ vertex balanced bipartite graph to be ...

**0**

votes

**0**answers

71 views

### Understanding the significance of the values of an adjacency matrix [closed]

I am new to network/graph theory and I am trying to understand a few things. One of these is the significance of the i,j entry of an Adjacency Matrix. In an ...

**0**

votes

**0**answers

66 views

### Missing count in number of perfect matchings

Let $f(G)$ give the number of perfect matchings of a graph $G$.
Consider set $\mathcal N_{2n}=\{0,1,2,\dots,n!-1,n!\}$.
Consider collection of all $2n$ vertex balanced bipartite graph to be ...

**0**

votes

**1**answer

254 views

### Efficient isomorphic subgraph matching with similarity scores

I'm a computer vision PhD student, and I'm looking for an efficient approximation to the following problem, which could end up helping in image to image matching. Failing that, pointers to relevant ...

**4**

votes

**1**answer

66 views

### Degree of neighbors in a simple graph (friendship paradox variant)

Context: this question is a translation of a common informal phrasing of the friendship paradox ("Most people have fewer friends than most of their friends"). Note that the question is similar to, but ...

**3**

votes

**1**answer

56 views

### Maximal acyclic subgraph

It is well known that the problem of finding a maximal acyclic subgraph of a digraph is NP-complete.
Is this the case also when the digraph is symmetric ,i.e. if $(a,b)$ is a link, then $(b,a)$ is ...

**0**

votes

**0**answers

11 views

### Prove that the converse of a strong digraph is also strong [closed]

I would like to know how I prove this.
The converse of a digraph D is obtained from D by reversing the direction of every arc of D. Show that a digraph D is strong if and only if its converse is ...

**19**

votes

**3**answers

548 views

### Which paths in a graph are orthogonal to all cycles?

Start with some standard stuff. Suppose we have a directed graph $\Gamma$. I'll write $e : v \to w \,$ when $e$ is an edge going from the vertex $v$ to the vertex $w$. We get a vector space of ...

**2**

votes

**0**answers

48 views

### Universal path function for all small trees

Let $f$ be a function $f: [k]^2 \rightarrow [k]$ (Where $[k]$ is the set $
\{0,1,\dots,k-1\}$).
A function $f$ is called $n$-universal path function if for every tree $T$ with $n$ vertices there ...

**0**

votes

**3**answers

98 views

### How to do a clockwise ordering of a planar graph in order to define its faces?

I am currently making an algorithm for planar graphs that I need to triangulate so they become maximally planar (that is triangulated and planar) given only the lists of neighbors for each node : no ...

**1**

vote

**1**answer

229 views

### Hashimoto Matrix (Non-backtracking operator) and the Graph Laplacian

The question is: how can we recover the graph Laplacian or its spectrum from the Hashimoto Matrix (also commonly called the Non-backtracking operator)?
To make the question as self-contained as ...

**9**

votes

**2**answers

596 views

### Expected number of connected components in a random graph

For a random graph G(n,p) what is the expected number of connected components? What is the probability distribution of this value?
I'm specially interested in what happens for small values of p, ...

**2**

votes

**1**answer

74 views

### Do product distributions (or graph products) eventually cluster as more products are taken?

Say we have a joint distribution on a finite alphabet $\mathcal{X}\times \mathcal{Y}$. It could be a communication link where we want to send a random message $X$ over a channel, but it gets garbled ...

**4**

votes

**1**answer

204 views

### minimal polynomial for a graph

I wonder if there is any result relating the degree $d$ of the minimal polynomial of a directed finite graph to any of its topological features - such as its diameter, or any other similar 'natural' ...

**6**

votes

**1**answer

434 views

### How to find or constrain “particularly good” (two-sided) spectral expanders?

I'm new to graph theory, but a response to a question I asked a while ago introduced me to the concept of expander graphs.
A k-regular graph (henceforth "graph") on n nodes has eigenvalues k = λ1 ≥ ...

**4**

votes

**2**answers

5k views

### Reporting all faces in a planar graph

Hi, I was looking to traverse a planar graph and report all the faces in the graph (vertices in either clockwise or counterclockwise order). I have build a random planar graph generator that creates a ...

**3**

votes

**2**answers

133 views

### Characterizing graphs whose Incidence Matrix has the all ones vector in its row span

Suppose we have a simple connected graph $G=(V,E)$. Then let $A$ be its $|E|\times |V|$ incidence matrix. Here I am considering the unoriented incidence matrix. I want to known when the row span of ...

**3**

votes

**0**answers

31 views

### how to study the size of basins of attraction on a graph

I have a certain finite (but huge and without an apparent pattern, so that only numerical studies seem feasible) graph $G = (V,E)$, and a function $f: V \rightarrow \mathbb{R}$. On each edge $e = ...

**4**

votes

**1**answer

80 views

### Choice number of embedded graphs

For given $g$, consider the family of graphs which may be embedded to the compact orientable surface of genus $g$. For this family, consider maximal clique $\alpha(g)$, maximal chromatic number ...

**1**

vote

**0**answers

55 views

### bounded degree graph colouring.

I was wondering if anyone could provide references on the following:
Is determining the chromatic number of a bounded degree graph APX-complete?
2.I've seen the result that states it is NP-hard ...

**2**

votes

**0**answers

45 views

### Hypergraph edge colouring

I'm interested in knowing if finding the edge-chromatic number of a $k$-uniform $k$-partite hypergraph is NP-hard for $k\geq 3$ Could anyone provide a reference for the result? By edge-chromatic ...

**2**

votes

**1**answer

133 views

### Product and coproduct for bipartite graphs

Consider the category $BiGraph$ of bipartite graphs (vertices are named "places" and "transitions" like in Petri nets) and continous maps. A subgraph is named open iff it is place-bordered, and a map ...

**1**

vote

**1**answer

89 views

### Assigning random orientation to an edge in a regular graph

Given a simple regular graph of degree $d$ on $n$ vertices.
Assume an ordering of vertices and assume all orientations of edges is from $i$ to $j$ if edges $ij$ exists and $i<j$. Pick $m$ random ...

**19**

votes

**3**answers

1k views

### A generalization of the triangle counting problem for simple weighted graphs

One nice identity is that $$\operatorname{tr}(A^3)/6$$ counts the number of triangles of a graph with adjacency matrix $A$. It also implies that triangle counting in a graph can be performed in ...

**-3**

votes

**1**answer

64 views

### Connected homogeneous graphs [closed]

Let's call a simple, undirected graph $G=(V,E)$ homogeneous if for every $v,w\in V$ there is a graph isomorphism $\varphi:G\to G$ such that $\varphi(v)=w$.
It is clear that every finite homogeneous ...

**0**

votes

**1**answer

55 views

### Reference for Turan Density

I am working a 3-graph problem. I convert it to calculate Turan density, that is $lim_{n\to \infty}\frac{ex_3(n,F)}{\binom{n}{3}}$, where F is a3-graph. I'd like to know are there some methods and ...

**14**

votes

**3**answers

402 views

### Spectral theory of graph Laplacian besides $\lambda_2$

Most of what I've seen about the spectral theory of the graph Laplacian concentrates on $\lambda_2$, the second-smallest eigenvalue. This eigenvalue contains information regarding the connectivity of ...

**3**

votes

**1**answer

173 views

### A spectral graph theory problem

Let $S$ be a zero-free subset of the group ${\bf Z}_2^n$ and $\Gamma={\rm Cay}({\bf Z}_2^n,S)$ be a bipartite Cayley graph. For some choices of $S$, the graph $\Gamma$ has $4$ distinct eigenvalues, ...

**4**

votes

**1**answer

90 views

### Behaviour of eigenspaces of adjacency matrices after a single change to the graph

Say I know the eigenvalues and eigenvectors of an adjacency matrix of an unweighted graph. Can I say anything about the eigenvalues and eigenvectors of an adjacency matrix of a graph with one extra ...