Questions tagged [graph-algorithms]

Algorithms on graphs, excluding heuristics.

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27 views

Latest results on the k-stacker crane problem?

I was searching for the $k$-stacker crane problem on google scholar but the best known result is dated back to 1976 with the original paper. I'm unsure whether there would be newer results of the ...
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39 views

Generalizing PageRank for tripartite graphs

Problem I have the following directed tripartite graph $G(E\cup V\cup P, A)$, where there is a many-to-one symmetric relationship between the subsets V and E - $e\in E,v\in V,[e, v]\in A \iff [v, e]\...
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1answer
84 views

Approximating Independent Dominating set on bipartite graphs

I'm interested in the following problem: given a bipartite graph, find the smallest independent set of vertices which dominate all other vertices. My question is: are there any positive results in the ...
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91 views

Graph recovery from pairwise-common neighborhoods

Define the common neighborhood of two vertices $u$ and $v$ of a simple undirected graph as the set $N(u,v)=N(u)\cap N(v)$. For a simple bipartite graph $G=(U,V,E)$, define the pairwise-common ...
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29 views

Maximum cliques of the transitive closure of a chordal DAG

Let $G=(V,A)$ be a directed acyclic graph, for which the underlying undirected graph is chordal (so that every induced cycle in the underlying undirected graph is a triangle). It is known that in a ...
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84 views

Minimum spanning tree, but with an unusual objective function

This is a problem that came up in my study of rumour networks. I was wondering if anyone had thoughts or references on this problem. If we have a rooted tree $T = (V,E)$ with root $r$, I first label ...
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1answer
264 views

STCONN in $O(n)$ time?

This is a very basic question on $s$-$t$-connectivity in directed graphs. As a baseline, using DFS (or BFS), one can solve the problem on a graph $G=(V,E)$ in $O(n+m)$ time and $O(n)$ space, where $n=|...
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1answer
37 views

Bipartite graph projections, with threshold

Let $G=(\top,\bot,E)$ be a bipartite graph: $E\subseteq \top\times\bot$. The projections $G_\bot = (\bot,E_\bot)$ and $G_\top = (\top,E_\top)$ of $G$ are defined as follows: two vertices are linked ...
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1answer
32 views

Maximum weight matching with classes of edges in a multi-edge bipartite graph

Posted a similar question in mathoverflow, have tried to reduce this to Ford Fulkerson, but been stuck. Thought I'd ask TCS community to see if there are any ideas from individuals, here. Consider a ...
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315 views

Is that edge orientation optimization problem NP-hard?

Is the following optimization problem NP-hard? Problem. For a given undirected graph $G=(V,E)$, find an orientation of the edges that minimizes the objective value $\sum_\limits{u\in V} ~\left( d_{...
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1answer
206 views

Is this edge orientation optimization problem NP-hard?

Is the following optimization problem NP-hard? Problem. For a given undirected graph $G=(V,E)$, find an orientation of the edges that minimizes the objective value $\sum_\limits{v\in V} ~d_{out}(v)\...
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148 views

Is this node permutation optimization NP-Hard?

Let $G=(V,E)$ be an undirected graph and let $\pi$ be a permutation of the vertices in $V$. For a node $v\in V$, we denote by $\text{succ}_{\pi}(v)$ the set of neighbors of $v$ that occur after $v$ in ...
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75 views

Dynamic connectivity with known history, for maximal connected component span

Consider a graph in which edges are added and removed over time. Define the span of a connected component as the product of its number of vertices and the longest duration for which it remains a ...
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Is this problem in P? Given a bipartite graph, find a minimum cardinality set of edges which intersect every vertex cover

This problem came up in my study of digraphs: Given a connected bipartite graph $G = (A \cup B, E)$, a vertex cover is a set $S$ of vertices such that every edge has some endpoint in $S$. Note that $A$...
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2answers
86 views

Name of this graph partitioning problem? (related to coloring)

Given a graph $G=(V,E)$ and an integer $k$, find a partition $P_1, P_2, \dots, P_k$ of $V$ into $k$ parts that minimize the total number of edges between two vertices in the same part, i.e. $\sum_i |(...
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1answer
50 views

Problem conditions to use Laplacian solvers

I am trying to use Laplacian Solvers to solve a linear equation. I am just learning it (form here), so my question is very basic and it might not even make sense. Suppose that we want to solve Ax=b, ...
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25 views

Pagerank update upon vertex removal

Assume we have computed the Pagerank of the vertices of a given graph. Then, remove a vertex from this graph, with all its edges. How to efficiently compute the Pagerank of remaining vertices in the ...
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1answer
112 views

A stronger Flow Decomposition Theorem?

In the classic Network Flows: Theory, Algorithms, and Applications book (pages 80/81) the flow decomposition theorem is stated as follows: Every nonnegative arc flow x can be represented as a path ...
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185 views

Is the Triangle Finding decision problem in $coNTIME(\tilde{O}(n^2))$?

The Triangle Finding decision problem asks whether there exists a triangle in a graph $G$ containing $n$ vertices. A triangle is a triple of vertices $(a, b, c)$ such that $a$ is adjacent to $b$, $b$ ...
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1answer
35 views

Multi agent path following with collision avoidance with pre-determined path

I am working on a multi-agent pathfinding algorithm. I am aware of other techniques, but planned on the folowing strategy only. The problem: There is 12x12 grid, with a few solid blockades within them....
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29 views

Optimum partitioning of vertices into mutually disjoint subsets in a weighted graph

tl;dr I'm trying to partition my students into groups with respect to their preferences, i.e. they can declare if they want to be with someone in a group or if they do not want to be with someone in a ...
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1answer
81 views

Dynamic transitive closure with immediate new reachability facts

The typical definition of dynamic transitive closure (or reachability) uses two types of queries: the first one is an update (edge deletion/insertion) and the second one is a reachability query. Thus, ...
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1answer
109 views

Minimal clique edge cover vs minimalist (assignment-minimum) ones

Given a graph $G=(V,E)$, a clique edge cover is a collection $C$ of subsets of $V$ such that each element $c$ of $C$ is a clique ($c \times c \subseteq E$) and $G$ is the union of these cliques ($E = \...
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1answer
72 views

Has this bipartite graph problem been studied?

I have a directed bipartite graph with vertex sets $U$ and $V$, directed edge sets $E(U,V)$ and $E(V,U)$, and a demand function $d \colon U \rightarrow \mathbb{Z}$. I want to find a function $f \colon ...
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1answer
139 views

Obtaining Sets of Ancestors Quickly in a Directed Acyclic Graphs

Suppose I have a DAG, $G = (V, E)$ and we know that all nodes in the DAG have at most $A$ ancestors. Let $V' \subseteq V$ be a subset of vertices of $V$. Is there a way to obtain the set of all ...
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118 views

Triangle counting using approximate matrix multiplication — suspicious paper

This paper [1] claims that for matrices with entries in $O(1)$, one can approximately multiply them in time $O(n^2 \log 1/\delta)$ to within error delta in the Frobenius norm (Theorem 1 in that paper)....
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44 views

Counting subsets of bipartite graph part which admit an induced perfect matching

Given a bipartite graph $G=(U \sqcup V, E)$, count $U^\prime \subseteq U$ for which $\exists V^\prime \subseteq V$ such that the induced subgraph $G[U^\prime \sqcup V^\prime]$ contains a perfect ...
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460 views

Linear-time algorithm to test if clique number equals degeneracy bound?

Given a connected simple graph $G=(V,E)$, let $d$ denote its degeneracy and let $\omega$ denote the size of a maximum clique. A well-known bound on the clique number is $\omega\le d+1$, which is ...
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130 views

Is 4-Coloring restricted to graphs with crossing number 1 NP-complete?

Planar graphs are 4-colorable. Determining if a planar graph is 3-colorable is NP-Complete. A graph with a crossing number 1 (graph such that it can be drawn with $\le 1$ crossing) is 5-colorable. ...
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58 views

Can we always find a graph with a given algebraic connectivity?

This is crossposted from math stackexchange. This is my first time posting here, so let me know if I'm doing something wrong. I would like to experiment with various spectral properties of graphs, ...
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40 views

Gradient descent on k nearest neighbor graph

I wanted to know how gradient descent can be used to minimize the distance function in approximate k nearest neighbor algorithm as mentioned in paper "Efficient K-Nearest Neighbor Graph ...
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118 views

Finding nodes with enough unique ancestors

Given a DAG $G = (V, E)$, let $T \subseteq V$ be a set of nodes of $V$ that is computed via the following process. Assuming the nodes of $G$ are sorted in topological order, $v_1, \dots, v_n$. We ...
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1answer
62 views

Separating DAGs using separators consisting of lists of nodes and all ancestors

Suppose we are given a DAG, $G = (V, E)$ where $n = |V|$. We consider the sets $J_1, J_2, \dots, J_n$ to be lists of vertices where list $J_i$ consists of vertex $v_i \in V$ and all ancestors of $v_i$....
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37 views

Remove cycles from a stochastic comparison matrix, while doing the least amount of editing

Let $\mathcal P_n$ be the collection of all matrices $M \in [0, 1]^{n \times n}$ such that $M_{ij} + M_{ji} = 1$ for all $i, j \in [n]$. Such matrices are called comparison matrices. A comparison ...
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1answer
41 views

Best approximations of Minimum Dominating Sets in chordal graphs

I am searching results and papers related to the (in)approximability of the Minimum Dominating Set problem in chordal graphs. In particular, what is the best approximation ratio achievable in polytime ...
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15 views

Power of Hyperedge Replacement Grammars (HRGs)

Can HRGs generate languages which equal or include the following graph languages: All (bipartite) graphs of bounded degree All (bipartite) planar graphs of bounded degree All (bipartite) planar ...
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75 views

Forbidden Subgraph Characterization for Graphs with few Maximal Cliques

Consider the following property of undirected graphs. A graph has the $s$-vertex overlap property if every vertex is contained in at most $s$ maximal cliques. I am interested in forbidden induced ...
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82 views

Minimum feedback arc set for dense directed graph

This is really a matrix problem, but the theory I believe lies in graphs. Consider some matrix $A$ and permutation matrix $P$, where we define $\tilde{A}:= PAP^T$. I want to pick $P$ such that if $\...
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160 views

Complexity of Edge Coloring Regular Graphs With Large Degrees

There is an interesting series of papers on edge colorability / $1$-factorization of regular graphs with large degrees, which over the years have shown better and better lower bounds for the degree $\...
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72 views

Calculation of sum of weights of nodes in a tree graph

Updated There's a real production project related to real estate properties around the world. The data has a structure of nested nodes. E.g. end nodes which have no outgoing edges (red) are properties ...
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1answer
150 views

Isomorphism of ‘ordered’ DAGs / acyclic semiautomata

I am wondering what is known about the isomorphism problem on ordered DAGs, in particular how to find a canonical representative modulo isomorphism. By ordered I mean that each vertex has a list of ...
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1answer
78 views

Generate cut $(A,B)$ in edge-colored graph $(V,E_1 \cup E_2)$ such that there are more red than white crossings, i.e $|E_1(A,B)| > |E_2(A,B)|$

Let $G=(V,E)$ be graph. Recall that a cut of $G$ is (or can uniquely be identified with) a pair $(A,B)$ of nonempty subsets of $V$ which partition it. Given a cut $(A,B)$, let $E(A,B) := \{(a,b) \in ...
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1answer
117 views

Graphs-like data structure with weighted vertices

I am searching for literature related to a graph-like data structure where vertices are weighted instead of edges. Formally, we can define a weighted-(edge)-graph $G=(V,E, w(\cdot))$ as a tuple of ...
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1answer
101 views

Complexity of acyclicity of a “nondeterministic” graph

By "nondeterministic" I mean the graph is a collection of sets of "candidate" edges sharing a single destination: $E \subseteq 2^V \times V$. The problem is whether it is possible ...
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34 views

granularity of bidirectional breadth-first search

I tried posting this on stack overflow and it got no takers, decided to cross post here: One thing that I've never seen discussed about bidirectional breadth-first-search (which I'll abbreviate as ...
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1answer
77 views

Sample graph dataset for testing algorithms

I hope I'm addressing the right community. For a project for my students, I need to find some weighted graphs (oriented or not) to benchmark their algorithms (shortest paths, flows...). There are a ...
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52 views

The Edge Cover Equilibrium Problem

Let the Edge Cover Equilibrium Problem be the following: INPUT: a simple undirected graph $G$. OUTPUT: YES, if the number of edge covers of $G$ having odd cardinality is equal to the number of edge ...
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116 views

Find min-weight simple path assuming no negative simple cycles

A simple path is a path that doesn't revisit a node. A simple cycle is a cycle that doesn't revisit an edge. You are given an undirected graph G which may contain edges of negative weight but which ...
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71 views

Comparing two graphs when starting from a single edge

Let's assume that we are given two graphs $G_1$ and $G_2$ defined by the two following nicely drawn pictures. Black numbers label the nodes, red numbers show the edge weight between the nodes. $G_1$ ...
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48 views

Find a boundary from set of 3d line segments

I have a set of n 3d line segments ...

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