Questions about properties of and problems on graphs, discrete data structures that have the form of nodes connected by edges, that is networks.

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14 views

Understanding the correctness of the Euler Tour Technique

I can't prove the correctness of the following algorithm by R. E. Tarjan amd U. Vishkin, as described on wikipedia: Given an undirected tree presented as a set of edges, the Euler tour ...
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0answers
13 views

Stable matching of producers, consumers and objects

Has the following version of the stable matching problem been studied? There are $k$ types of objects. There are $n$ producers, each of whom can produce a single object of any type, and has a ...
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1answer
30 views

undirected graph without weights and DFS [on hold]

following question on undirected graph without weights can be solved by using DFS and in O(|V|+|E|) times. check that G is ...
0
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2answers
82 views

Finding a Hamiltonian Path through the complete graph on 37 vertices: $K_{37}$ [on hold]

I'm planning on making a fiber art $K_{37}$ (like the one I laser etched with help: K37: The complete graph on 37 nodes, svg). To accomplish this, the plan is to construct 37 pegs equally spaced in a ...
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0answers
18 views

Is it possible to find closeness centrality using Gephi? [closed]

I'm a newbie to Gephi. I need to calculate the centrality measures. Is there an option/plugin available to calculate them ?
4
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1answer
44 views

Parameters for Barabasi-Albert graph generator

I'm trying to reproduce the synthetic networks (graphs) described in some papers. It is stated that the Barabasi-Albert model was used to create "scale-free networks with power-law degree ...
2
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1answer
24 views

Examples for directed graphs with super polynomial cover time

The cover time of a graph is the expected number of steps in a random walk on the graph until we visit all the nodes. For undirected graphs the cover time is upperbounded by $O(n^3)$. What about ...
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0answers
16 views

Distance Increment in Graphs [closed]

Question: Let G be a direced graph with non-negetive weights and to speciall nodes S and T,find the smallest group N (group of edges) that will increase the distance form S to T. Time ...
2
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1answer
81 views
+150

Equivalent Straight Line Embedding of a Planar Graph Drawing on a Grid

An embedding of a graph G on a surface Σ is a representation of G on Σ in which points of Σ are associated to vertices and simple arcs are associated to edges in such a way that: the endpoints of ...
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1answer
34 views

Not Hamiltonian is in NP Class? [duplicate]

I ask a question before, Questions on Graph and Hamiltonian, but i ask it here with different challenging contest. From this book and other study in complexity theory, I have seen the following ...
4
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0answers
26 views

Parallel algorithm to find if a set of nodes is on an elememtry cycle in a directed/undirected graph

I'm looking to find / develop a simple parallel algorithm that does this: Input: vs: list of root vertices max_length: max cycle length max_dist: max distance to root Variants one variant of ...
2
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1answer
71 views

Questions on Graph and Hamiltonian [closed]

From this book and other study in complexity theory, I have seen the following statement: The definition of NP is not symmetric with respect to yes-instances and no-instances. For example, it is ...
2
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1answer
33 views

What is an edge hop?

I've tried googling it, but found nothing. Here is the context it's in: From Bayesian Reasoning and Machine Learning: Adjacency matrices may seem wasteful since many of the entries are zero. ...
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0answers
61 views

Clique vs genus [migrated]

Is there a relation between Clique size $\omega(G)$ and genus $g(G)$ of a graph? That is does $$\omega(G)^c\geq g(G)\geq \omega(G)^{\frac{1}d}$$ hold with constants $c,d\geq1$?
2
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0answers
20 views

Heuristic for weighted maximum independent set in graph with ~$2 \times 10^5$ nodes and $|E| \propto |V|$

I want to find a near-optimal solution for a maximum weight independent set. i.e given a graph $G = (V,E)$ I want to find a set $S = \{v_1,v_2,\dots,v_n\}$ of nodes in $V$ such that the sum of their ...
4
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1answer
79 views

Term for a matching which is perfect on one side only

What is a standard term for a matching in a bipartite graph, in which one part has less vertices than the other part, and the part with less vertices is fully matched (but the other part is, ...
0
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0answers
10 views

Solving $Isomorphism$ using $AUTOM$ in polynomial time

Let $Iso$ be the language of all $<G,H>$ such that $G$ and $H$ are isomorphic, and $AUTOM$ be the language of all $G$'s such that $G$ has a non-trivial automorphism. I'd like to show that, ...
0
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2answers
31 views

A* graph search heuristicfor pathfinding

A* needs a consistent heuristic to work on a graph. So I'm not sure if the heuristic of a straight line (bird flight) can be used. For example: the costs to travel to a neighbors node is always ...
0
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1answer
22 views

Reweight general weighted graph to distinct graph for using Borůvka's

Is it possible to re-weight a generally-weighted graph to a distinctly-weighted graph to apply Borůvka's algorithm (wiki) for minimum spanning tree to it? I can't seem to think of a way to make a ...
2
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1answer
54 views

Reduction from a further constrained problem

If I find an NP Hard problem that is equivalent to my problem with an additional constraint or bound, can I still prove that my problem is NP Hard? Generally, this is probably not the case. For ...
1
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3answers
95 views

How can I evaluate an algorithm for a NP-Hard problem?

I have written a program to calculate the number of stable partition in a graph. ( That is: find which partition of the nodes does not have edges between nodes of the same block. ) The professor, ...
2
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0answers
43 views

Constructing orthogonal latin square Parker/Knuth method

I'm working through Knuth; The Art of Computer Programming, Vol. 4 Fascicle 0 and I'm having a little trouble making sense of the method Knuth describes for computing an orthogonal latin square. The ...
3
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1answer
82 views

Linear programming formulation of cheapest k-edge path between two nodes

Given a directed graph $G = (V,E)$ with positive edge weights, find the minimum cost path between $s$ and $t$ that traverses exactly $k$ edges. Here is my attempt using a flow network: \begin{align} ...
2
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0answers
55 views

What is a best known algorithm for finding diameter of undirected graph?

What is best known algorithm (approximate or exact) for finding diameter of a large undirected graph? The diameter is defined as longest of shortest paths between any two nodes. I know that naive ...
4
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0answers
56 views

Recognize if graph has Hamiltonian cycle from subgraphs

There is a graph G, which is not known to me. Instead I am given the multiset of all graphs that are obtained by deleting a single vertex from G. My task is to figure out, from all of these subgraphs, ...
0
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1answer
60 views

Finding undirected cycles in linear time (triangulating graphs while minimizing degree)

In the article ["Triangulating Planar Graphs While Minimizing the Maximum Degree"] by Kant and Bodlaender [1], Section 4 briefly mentions the extraction of elementary cycles (no repeating ...
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3answers
81 views

Given a minimum vertex cover can we find all the others in polynomial time?

Having found one minimum vertex cover of a connected undirected graph, is there a known polynomial-time algorithm for finding all the other minimum vertex covers of the graph, or is this problem ...
1
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0answers
54 views

Maximum flow problem with non-zero lower bound

Given $G = (V,E )$ a directed graph, if $ X \subseteq V $ we write $$\begin{align*} \delta ^{+}(X) &= \{ xy\in E \mid x \in X, y\in V - X \} \\ \delta ^{-}(X) &= \delta ...
0
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1answer
33 views

To detect isomorphic graphs Is it enough to check if they have the same number of same degree vertices?

Given two lists of non directional graph edges e.g. [(1,3),(3,5),(5,1),(5,7)] [(4,5),(2,3),(3,4),(4,2)] In order to check if the two graphs are isomorphic is it enough to count the vertices with the ...
1
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1answer
56 views

“Minimum” maximum flow with extra capacities

Problem: Suppose there is a graph, a source and a sink. Each edge has a capacity and an extra capacity that it can hold. If sink needs a defined amount of flow F, ...
0
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0answers
18 views

Algorithm: “Minimum” maximum flow with extra capacities [duplicate]

Problem: Suppose there is a graph, a source and a sink. Each edge has a capacity and an extra capacity that it can hold. If sink needs a defined amount of flow F, ...
0
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0answers
38 views

Stable Marriage or Assignment Problem?

I have a question pertaining to committee selection. Let $C = c_{1}, c_{2}, \ldots, c_{n}$ be n Committees and $S = s_{1}, s_{2}, \ldots, s_{m}$ be m Students. Each $c_{i}$ in C ranks their ...
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1answer
62 views

Knight's tour from all starting positions

Is it true that for all $n\geq 5$, there is a knight's tour of an $n\times n$ chessboard beginning at every square? For example, is it correct, that there is no solution for a $5\times5$ board, with ...
3
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1answer
21 views

Do $s$-$t$ cuts partition contingent vertices?

The definition of an $s$-$t$ cut is a partition of the set of vertices $V$ into $2$ sets $(A, B)$ with $s$ in $A$ and $t$ in $B$. My understanding of set partitions is that the positioning of elements ...
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0answers
14 views

Graph Partition Across Cluster - Minimize Largest Matrix Size

I am writing some code for modeling semi-biologically realistic neural networks, which is to be run/distributed across nodes in a computer cluster. I begin with a very large adjacency matrix ...
9
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1answer
111 views

Determining the minimum number of edges to add in order to be 3-connected

A graph $G$ is said to be $3$-connected if it has no $2$-vertex cutsets (i.e., at least three vertices must be deleted to disconnect the graph). As far as I know, it is possible to determine if a ...
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2answers
44 views

Can't see how this can be true: any connected undirected graph $G$ contains vertex v such that removing v results in another connected Graph $G'$ [closed]

I am attempting to prove this result but I found a case where I can easily disprove this statement. Suppose $G$ is a graph with two nodes u, v and an edge (u,v) and respective self edges, then ...
4
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1answer
51 views

Distribution of cycles length in a graph

Given a random directed Graph G: $$ G=(V,E) \\ \lvert V \rvert = n , \lvert E \rvert = k $$ where for each vertex, either: $$ d_{incoming}(v) = 1 , d_{outgoing}(v) = 1 $$ meaning - for each ...
0
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1answer
42 views

Tournament graph

I have to prove the following assertion: given a tournament graph with $n$ vertices, $n\geq 5$, there can be made an arrangement of the arcs such that between any two vertices exists at least one way ...
2
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0answers
43 views

Necessary and sufficient condition for unique minimum spanning tree

This is an exercise problem (Ex.3) from the excellent lecture note by Jeff Erickson Lecture 20: Minimum Spanning Trees [Fa’13] . Prove that an edge-weighted graph $G$ has a unique minimum ...
2
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2answers
45 views

Difference between edges in Depth First Trees

I have a directed graph, where each node has an alphabetical value. The graph is to be traversed with topological DFS by descending alphabetical values (Z-A). The result is $M,N,P,O,Q,S,R,T$ (after ...
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1answer
28 views

Vertex degree in De Bruijn graphs

How can I find the degree of a vertex in a De Bruijn graph? Also, given a vertex, is there an easy way to find which other vertices it is connected to?
3
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1answer
59 views

Assign undirected edges in a mixed graph to make graph cyclic/acyclic

What is the complexity of the following problem? Given a mixed (some edges directed, some undirected) graph, assign a direction to all the undirected edges to make the graph contain a cycle. It ...
5
votes
3answers
294 views

Constructing a random Hamiltonian Cycle (Secret Santa)

I was programming a little Secret Santa tool for my extended family's gift exchange. We had a few constraints: No recipients within the immediate family Nobody should get who they got last year The ...
0
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0answers
15 views

Prove a characterisation of the minimum directed cycle mean cost

Let $\mathcal G = (\mathcal V, \mathcal A)$ be directed graph with associated edge costs $c_{i,j}$ that has at least one directed cycle. Define the directed cycle mean cost to be $\frac {\{\text {sum ...
3
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1answer
84 views

Given an optimal solution to the LP, show how it can be used to construct a directed cycle with minimal directed cycle mean cost

Let $\mathcal G = (\mathcal V, \mathcal A)$ be directed graph with associated edge costs $c_{i,j}$ that has at least one directed cycle. Define the directed cycle mean cost to be $\frac {\{\text {sum ...
5
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1answer
72 views

Finding $k$ claws ($K_{1,3}$ bipartite graphs) in a graph?

Usually questions deal with claw-free graphs, but suppose we are given a graph $G$ and there are $k$ vertex-disjoing claws in the graph, how can we derive a randomised algorithm using color coding to ...
7
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2answers
292 views

What is the most efficient algorithm and data structure for maintaining connected component information on a dynamic graph?

Say I have an undirected finite sparse graph, and need to be able to run the following queries efficiently: $IsConnected(N_1, N_2)$ - returns $T$ if there is a path between $N_1$ and $N_2$, ...
1
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1answer
65 views

Formulate the Marriage Problem into a Maximum-flow problem (Graph theory)

Suppose I have $M=\{1,\ldots, n\}$ men and $W = \{1, \ldots, n\}$ women and $B =\{1, \ldots, m\}$ brokers, such that each broker knows a subset of $M \times W$ and for each pair in this subset a ...
0
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1answer
41 views

Single Source Shortest Path: What does the weights on the vertex and edges tell you?

In MIT's open courseware (http://courses.csail.mit.edu/6.006/spring11/lectures/lec15.pdf), I do not see how computing a set of numbers on the edge and the vertex will produce the shortest path. ...