Questions tagged [graph-theory]

Graph theory is the study of graphs, mathematical structures used to model pairwise relations between objects.

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Question about claw-free graphs

Let $G$ be a claw-free graph, and let $x,y,z,u$ be distinct vertices of $G$. Is the following possible in $G$ ? There are three induced paths through $u$: between $y$ and $z$ (i.e., $y \...
1 vote
3 answers
537 views

Minimum number of triangles required to cover a complete graph?

Let $K_n$ be a complete graph, I am interested in knowing the minimum number of triangles required to get a edge cover of $K_n$. In case there is no closed-form solution to this problem, then I would ...
0 votes
0 answers
55 views

Is every 4-claw-free graph a bounded degree graph?

I am looking of some graph properties of 4-claw free graph, where neighborhood of every vertex has independent set of size at most 3. As per my observations, this type of independent set size ...
2 votes
2 answers
163 views

property of minimal triangulations

A graph is chordal if every cycle on four or more vertices contains a chord i.e. an edge between non-adjacent vertices of the cycle. A triangulation (or chordalization) of a graph $G=(V,E)$ is the ...
2 votes
1 answer
292 views

A non-trivial combinatorial optimization

So I stumble over this problem in which I couldn't find anything similar in the literature. I am not even sure if it is NP-hard or solvable in polynomial time. Any thought or suggestion would be ...
0 votes
0 answers
125 views

Error in TAOCP 4a on the bipartite graph constructed from a hypergraph

The first sentence on page 33 of Donald Knuth's The Art of Computer Programming (TAOCP) Vol. 4a reads: Furthermore, a hypergraph is equivalent to a bipartite graph with vertex set $V \cup E$ and ...
3 votes
1 answer
69 views

What is the fastest algorithm for computing exact network reliability?

In the network reliability problem, we are given an undirected graph $G$ on $n$ vertices and a parameter $p\in (0,1)$, and are tasked with determining the probability that $G$ becomes disconnected (i....
1 vote
0 answers
122 views

Upper bound on the number of maximal paths in rooted intransitive DAGs

Let $D(V, A)$ be a DAG. Definition 0: We name a path between two nodes $i$ and $j$ as an $i$-$j$-path. Definition 1: Let $p$ be a path, we call $|p|$ the path length, representing the number of arcs ...
0 votes
1 answer
167 views

Finding the shortest cycle containing a vertex in a graph

Given a connected undirected graph with edges $E$ and verticies $V$ and a vertex $v \in V$, find the length of the shortest cycle containing $v$. The best I could do is $O(|E|*deg(v))$, by trying to ...
3 votes
2 answers
156 views

Given a weighted graph with $pk$ nodes find a min weight forest with $p$ components each containing exactly $k$ nodes

Given a weighted graph with $pk$ nodes find a min weight forest with $p$ components each containing exactly $k$ nodes. Does this have a constant approximation? ($p,k$ and the graph are all part of the ...
5 votes
0 answers
120 views

What is the smallest graph of treewidth $k$ having less edges than the $(k+1)$-clique?

Treewidth is a graph parameter measuring how close a graph is to being a tree. I am interested in what is the minimal number of edges required for a graph to have treewidth $k$. A natural family of ...
8 votes
1 answer
2k views

How bad can the greedy coloring (list color) for the c-chromatic number of graph be?

c-chromatic number is defined in the paper Partitions of graphs into cographs. It asks for the minimum number of colors used to color vertices such that each color class is a cograph. Cograph is a P4-...
0 votes
0 answers
45 views

Is hypergraph reachability definable in MSO?

Let $(A,E)$ be a directed 2-uniform hypergraph and $E$ the corresponding binary relation such that $(X,Y) \in E$ iff there is a hyperedge from $X$ to $Y$. We say that there is a path from $X_1$ to $...
1 vote
1 answer
134 views

Efficient Algorithm for Partitioning a Directed Acyclic Graph into Short Paths

I am working on a problem involving partitioning a directed acyclic graph into distinct multiple paths, each with a maximum length constraint. The goal is to minimize the number of paths (this should ...
7 votes
1 answer
556 views

Connectivity of a random regular graph of degree $d$

An Erdős–Rényi graph over $n$ vertices and average degree $d$ is not connected w.h.p. iff $d < \log n$. I was wondering for what the degree $d$ would a random regular graph of degree $d$ be ...
2 votes
1 answer
196 views

Are there any implementations of a graph crossing algorithm?

This is much more focused version of this question: Are there good implementations for easy subclasses of NP-hard graph problems Computing the graph-crossing number $cr(G)$ for a simple graph is ...
3 votes
0 answers
97 views

maximum independent set in graphs with small number of edges

For the classic maximum independent set problem, a hardness of approximation result of $n^{1-\varepsilon}$ is known by [Hastad, 1996] assuming $\textsf{NP} \not \subseteq \textsf{ZPP}$, where $n$ is ...
5 votes
0 answers
56 views

How to prove that all pairwise independent hashing circuits are superconcentrators?

It is mentioned in Tight bounds on computing error-correcting codes by bounded-depth circuits with arbitrary gates, A. Gal et al. that "it is also not hard to show that (pairwise-independent) ...
7 votes
1 answer
217 views

Counting the different subsets of nodes seen when iterating a subset through a directed graph

For a given directed graph $G = (V, E)$ (possibly with loops), and some $S\subseteq V$ define the operation $G(S) = \{ v\mid (u,v)\in E\text{ for some } u\in S \}$. Now consider the infinite sequence $...
1 vote
3 answers
109 views

Stable/Robust Traveling Salesman Approximation Methods

I was wondering if there are TSP approximations that are "stable". More specifically, consider the set $G = x_1, ..., x_n$ and the set $G^* = G \cup x_{n+1}$, where $x_i$ are points in $R^d$....
0 votes
0 answers
17 views

Any value in a formula that calculates (not look up) the 'order' of a 'Independent Edge Set' OR a 'I.E.S.' given an 'order' on complete graphs?

Any value or interest in a formula that calculates (not look up) the 'integer order' of a given 'Independent Edge Set' OR given an 'Independent Set' calculates the 'integer order' on Complete Graphs? ...
0 votes
2 answers
151 views

Bottom up TSP solution?

I'm not sure if this is something new or if I'm just not getting previous efforts. TSP can be thought of as a list of weighted links and nodes. If one takes the Nearest Neighbor (NN) of every node and ...
5 votes
1 answer
483 views

Can Lexicographic BFS be implemented in logspace?

Input: Given graph $G=(V,E)$ with vertices labeled in some order Output: Change the labeling of vertices such that the labeling starts $v_1$ as $u_1$. Next, label the neighbors of $v_1$ as $u_2,u_3,...
-1 votes
1 answer
77 views

Representation of binary strings by graphs and hypergraphs

Let $\Sigma$ be the set $\{ 0, 1 \}$, then the set of all finite binary strings of length $n$ is written as $\Sigma^{\star}_{n}$. Question: Which further ways of representing binary strings of length $...
4 votes
0 answers
76 views

Name for a cyclic path in a graph that visits every vertex while minimizing the maximum number of times a given vertex is revisited?

Me and my colleague are interested in whether anyone has looked into a generalization of Hamiltonian cycles where vertices can be revisited, but we want to minimize the maximum number of times a given ...
1 vote
0 answers
250 views

Graph partitioning to minimize sum of intra-partition edge weights

I've seen a lot of graph partitioning algorithms w/ the objective of minimizing the weight of inter-partition edges, (e.g. k-way partitioning) but haven't quite found anything on minimizing the total ...
1 vote
1 answer
625 views

Generate TSP instances with known optimal

Is there a known (polynomial in number of nodes) algorithm to generate TSP instances with known optimal value? The idea is to be able to generating arbitrary large instances with known optimal value,...
0 votes
1 answer
75 views

A variation of the longest path problem

What about finding a path of maximum length in a given graph which may contain cycles, with the constraint that a vertex (or an edge) can be visited at most X (say 2 or 3) times ? EDIT: X would be ...
0 votes
0 answers
65 views

How to reduce a code down to its configuration

I have built a system where from atomic information of a UI code I could generate a framework specific code. Here is the concept https://github.com/imvetri/ui-editor. For example, the user of this ...
1 vote
0 answers
80 views

Tractability of computing generalized hypertreewidth on bounded arity hypergraphs

Generalized hypertreewidth is a generalization of treewidth to hypergraphs. Unlike treewidth, it is not tractable, for a fixed width $k \in \mathbb{N}$, given a hypergraph $H$, to determine if $H$ has ...
1 vote
0 answers
88 views

Generalization of the Hamiltonian path problem on Grid Graphs

Fix a cost to each of these actions: move up, move down, move left, move right. I.e. fix some function $f: \{\text{move up, move down, move left, move right}\} \to \mathbb N$. Define the following ...
2 votes
4 answers
6k views

Complexity of greedy coloring

I was looking at some heuristics for coloring and found this book on Google books: Graph Colorings By Marek Kubale They describe the Greedy algorithm as follows: ...
0 votes
0 answers
83 views

5-color graph and minor

We have a 5-color graph G without 5-clique. The question is: is there a minor H of G that is a 5-clique? Here the minor definition. With "5-color graph G" I mean $\chi (G)=5$.
2 votes
1 answer
66 views

Upper Bound for distance-two chromatic number in terms of maximum degree

Let us consider simple,finite, undirected graphs. A distance-two colouring of a graph $G$ is a function $f:V(G)\to\{1,2,\dots\}$ such that $f(u)\neq f(v)$ whenever $dist_G(u,v)\leq 2$. A distance-two ...
1 vote
0 answers
33 views

Application LCL definition to vertex coloration

I'm reading the article "What can be computed locally?" by Naor & Stockmeyer and I struggle to understand the definition of an LCL they gave. Here is an extract: (page 2) An Locally ...
4 votes
1 answer
88 views

Independent set queries with preprocessing

Suppose we have a sparse undirected graph $G = (V, E)$ with $|E| = O(|V|)$, and we want to process it and then answer queries of the following type: given a set $A$, is it an independent set in the ...
1 vote
1 answer
50 views

What is known about the complexity of Network Diversion?

In the Network Diversion problem, we are given an undirected graph $G$ on $n$ vertices, with specified nodes $s$ and $t$ and specified edge $e$, and a positive integer $k$, and are tasked with ...
0 votes
1 answer
205 views

Transitive reduction not provably minimal [closed]

Working on finding minimal equivalent graphs, which unlike transitive reductions only allows for edge removals from the original graph. I was under the impression that if you allow for new edges to be ...
0 votes
1 answer
73 views

What's the exact complexity of a DFS if we revisit nodes?

By "revisit nodes," I mean if we didn't maintain a set of nodes we have visited. So the sum I'm examining is just the number of paths from a root to a node, across all roots and nodes. We'll ...
3 votes
1 answer
138 views

Approximative counting of matchings in a graph

The work by Jerrum & Sinclair (1989) describes an approximative approach to determining the number of matchings $|M_\ast(G)|$ in a graph $G=(V,E)$. The fundamental ingredient of the approximation ...
3 votes
1 answer
194 views

What is the treewidth of the 3D-grid (mesh or lattice) with sidelength n?

Here, by 3D-grid of sidelength $n$ I mean the graph $G=(V,E)$ with $V= \{1,\ldots,n\}^3$ and $E=\{( (a,b,c) ,(x,y,z) ) \mid |a-x|+|b-y|+|c-z|=1 \}$. I known how to get the treewidth of $n*n$ grid is ...
1 vote
0 answers
46 views

Notion between connected and strongly connected graphs

Let $G$ be a directed graph without loops (or even better an oriented graph). Let us assume that $G$ is finite. The graph $G$ is connected if its underlying graph $G^*$ is connected (i.e., for every ...
0 votes
0 answers
61 views

What is a combinatorial embedding?

I got a reviewer comment saying that I should consider using combinatorial embeddings rather than idk what I should call what I was doing topological embeddings?. But I'm confused because as far as ...
3 votes
1 answer
104 views

Maximum cardinality matching on DAGs

A question on computational complexity and graph theory. The problem of finding maximum cardinality matchings of undirected graphs (the largest selection of edges such that each vertex is "...
8 votes
0 answers
171 views

Can one find good distance-2-separators in planar graphs?

It is known that planar graphs admit "good" separators, allowing to design PTASes for specific problems such as MINIMUM INDEPENDENT SET by recursive separation of the graph. However, it ...
5 votes
0 answers
84 views

(Where) is determining the mixing time of an implicitly defined graph in the polynomial hierarchy?

Consider an implicitly defined graph; for example, let $G$ be a finite group generated with $n$ generators as $\langle g_1,g_2,\ldots g_n\rangle$ and let $\Gamma$ be the Cayley graph of $G$ under ...
4 votes
0 answers
123 views

Exploding number of homomorphisms

I'm trying to tackle the following problem: given two graphs $A$ and $B$, if there exists a graph $D$ such that $\hom(A, D) > \hom(B, D)$ (i.e. there is more homomorphisms from $A$ to $D$ than from ...
1 vote
0 answers
49 views

Bound on the treewidth of a graph from modular contraction

I cannot find a reference for this easy to prove result concerning the treewidth of a graph with respect to the treewidth of a modular contraction of it. Let $G=(V,E)$ be a graph. A module $M \...
1 vote
0 answers
64 views

Graphs such that every rotation system admits an embedding on a surface of small genus

Let $G$ be a finite, simple, undirected graph. What conditions on $G$ ensure that every rotation system of $G$ corresponds to a cellular embedding of $G$ on an oriented surface of small genus? (e.g. ...
1 vote
0 answers
49 views

Given several $a_i$-$r$ paths in a planar graph how ``balanced" of a tree rooted at $r$ can I make?

Suppose I am given distinct nodes $a_1,a_2,.., a_l, r$ and several $a_i$-$r$ paths $P_i$ in a planar graph $G$. I wish to construct a tree $T$ connecting $a_1,a_2,.., a_l, r$ that minimizes the ...

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