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Questions about the branch of combinatorics called graph theory (not to be used for questions concerning the graph of a function). This tag can be further specialized via using it in combination with more specialized tags such as extremal-graph-theory, spectral-graph-theory, algebraic-graph-theory, topological-graph-theory, random-graphs, graph-colorings and several others.

0 votes
1 answer
37 views

Cycle-Sculpturing with Minimal Vertex-Deletion

given a simple, finite and symmetric graph $G(V,E)$ with $n$ vertices and at least $n$ edges Question: how can the smallest set of vertices $W\subset V$ be calculated for which the graph induced by $ …
Manfred Weis's user avatar
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4 votes
Accepted

Efficient algorithm for graph problem

If $v_1$ and $v_l$ are fixed then constructing a minimum weight breadth-first tree of height $l{-}1$ and finally optimally attach vertex $v_l$. Iterating over all candidate pairs of $v_1$ and $v_l$ wo …
Manfred Weis's user avatar
  • 13.2k
1 vote

Complexity of maximum weight-sum matching for cycle graphs

With inspiration from the comments I arrived at the following idea: the maximum weight matching on the cycle is converted to a maximum weight matching on a path that is generated by splitting a vertex …
Manfred Weis's user avatar
  • 13.2k
1 vote
1 answer
54 views

Complexity of maximum weight-sum matching for cycle graphs

I need to determine a matching with maximal weight-sum for a cycle graph with positive, negative and zero edge-weights. Question: What is the fastest way of calculating such a matching? Because of t …
Manfred Weis's user avatar
  • 13.2k
0 votes
0 answers
23 views

Building hypercubes from the bottom up

let $H^k$ denote a $k$-dimensional hypercube in a complete symmetric graph $G(V,E)$ without self-loops and parallel edges; let $|V|=2^n$ be the number of vertices. setting $\mathbb{H}^0 := V$, i.e. th …
Manfred Weis's user avatar
  • 13.2k
2 votes
1 answer
224 views

Name for generalization of trees to digraphs

One definition of tree in graph theory could be as follows: A tree is a(n undirected) graph for which there is a unique (undirected) path between any pair of vertices. This suggest a possible defini …
Manfred Weis's user avatar
  • 13.2k
0 votes

Minimally 2-vertex-connected graphs?

$K_3$ is the only graph with a triangle that contains a bivalent vertex, and is a minimally vertex 2-connected graph (MV2CG). According to the two ears theorem every triangulated polygon with at least …
Manfred Weis's user avatar
  • 13.2k
1 vote

Minimally 2-vertex-connected graphs?

I conjecture that a a sufficient condition for a graph being minimally 2-vertex-connected is that it is $2$-vertex-connected and if every vertex $u$ is adjacent to some vertex $v$ of degree $2$ and c …
Manfred Weis's user avatar
  • 13.2k
0 votes
0 answers
32 views

Enumeration of flat integral $K_4$

Question: What is known about the enumeration of all $(a,b,c,d,e,f)\in\mathbb{N}^6_+: \\ \quad\operatorname{GCD}(a,b,c,d,e,f)=1\ \\ \land\ \exists \lbrace x_1,x_2,x_3,x_4\rbrace\subset\mathbb{E}^2:\ …
Manfred Weis's user avatar
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2 votes
2 answers
202 views

Isometric embeddings of metric $K_{n+1}$ in $\mathbb{R}^n$

Question: is it always possible to embed a complete, symmetric and metric graph $G$ with $n+1$ vertices isometrically in $\mathbb{R}^n$? I'm convinced it must be true, but can't remember having seen …
Manfred Weis's user avatar
  • 13.2k
0 votes

Random sample of spanning trees

A pragmatic solution would be to randomly shuffle the set of edges and assgning them their index in that random sequence as their weight and finally calculate the Minimum-weight Spanning Tree of the t …
Manfred Weis's user avatar
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2 votes
1 answer
124 views

Constructing optimal Hamilton cycles from optimal Hamilton paths

Question: can the shortest Hamilton cycle in a complete symmetric graph with weighted edges be constructed from the shortest Hamilton path in the same graph by connecting its ends and then exchanging …
Manfred Weis's user avatar
  • 13.2k
0 votes
0 answers
89 views

Relation of minimum spanning trees to the shortest Hamiltonian path problem

Spanning trees can be decomposed into a minimal set of maximal path graphs, whose vertices have degree two exactly if they also have degree two in the spanning tree; lets call these paths tree paths. …
Manfred Weis's user avatar
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2 votes

$A^*$ algorithm to find shortest path when weights in my graph are the inverse of distance

The essential difference is that improvements to a shortest known connection between start and destination will most likely lead over intermediate points that lie outside a region that is not quite an …
Manfred Weis's user avatar
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2 votes
2 answers
122 views

Existence of certain regular graphs

Question: what can be said about the existence of $2k$ regular graphs, $1\lt k$ that have a $1$-factor and a $2$-factor? Provided their existence, what is/are the smallest for $k$? The graphs must b …
Manfred Weis's user avatar
  • 13.2k

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