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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.

2 votes
0 answers
68 views

Is this infinite family of non-trivial snarks resulting from the first Celmins-Swart?

Non-trivial snark is cubic graph with chromatic index $4$, girth at least $5$ and doesn't to contain three edges whose deletion results in a disconnected graph, each of whose components is nontrivial. …
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3 votes
1 answer
103 views

Let $S$ be the nonempty set of strongly regular graphs with given parameters. Must $S$ conta...

As the title says, let $S$ be the nonempty set of strongly regular graphs with given parameters. Must $S$ contain vertex transitive graph? I suspect the most likely counterexample would be $|S|=1$.
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2 votes
0 answers
124 views

Maximizing the minimum outdegree of digraph without $m$ cycle

Let $G$ be a simple digraph on $n$ vertices without a directed cycle of length $m$ (it may have directed cycles of length less than $m$. The cycles need not be simple). How large the minimum outde …
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1 vote
0 answers
47 views

Complexity of computing the Tutte polynomial of multigraph when the Tutte polynomial of the ...

Let $G$ be multigraph with $l$ loops and $m$ multiple edges and $G'$ be the underlying simple graph (loops and multiple edges removed). Assume the Tutte polynomial of $G'$ is given. Q1 What is th …
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5 votes
1 answer
218 views

Complexity of counting MAXCUT in planar graphs -- seemingly contradicting claims

Confusion is likely. Appears to me two papers give contradicting claims about the complexity of counting MAXCUT in planar graphs. Exact Max 2-SAT: Easier and Faster p. 6 However, counting the num …
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0 votes
0 answers
154 views

For which matrices deciding permutation similarity is polynomial?

Q1 For which matrices deciding permutation similarity is polynomial? It is not easier than graph isomorphism (and very likely is equivalent to it). If necessary, assume the entries are nonnegati …
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2 votes
1 answer
180 views

Graph classes where finding explicit coloring have certificate that it is minumum

Graph coloring doesn't have certificate that smaller coloring doesn't exist in general. I am looking for graph classes where finding explicit coloring is not polynomial and have polynomially verifiab …
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2 votes
1 answer
259 views

The edge chromatic number and pefectness of inflation of cubic graph

The inflation of graph $G$ is a graph $I(G)$ which is obtained by replacing each vertex $x$ by a complete graph $K_{\deg(x)}$ and joining each edge to a different vertex of $K_{\deg(x)}$. Let $G$ b …
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4 votes
1 answer
957 views

Coloring tensor products of graphs

Let $ G,H $ are simple finite graphs and $A = G \times H$. Here $ G \times H $ is the tensor product (also called the direct or categorical product) of $ G $ and $ H $. Let $G$ has smaller chromatic …
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1 vote
1 answer
98 views

Would a graph with such maximum weighted matchings exist?

Edit Tony's answer is quite nice, but I meant something else. Sorry for editing again, I meant edges. I am looking for a graph with 3 distinguished edges $xx'$,$yy'$,$zz'$ where $\deg(x)=\deg(y)=\deg …
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2 votes
0 answers
87 views

Complexity consequence of logarithmic boolean width of co-bounded degree graphs?

The paper On graph classes with logarithmic boolean-width claims that the boolean width of co-k-degenerate graphs is at most $k\log{n}$ and a lot of graph vertex partition problems can be solved in po …
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2 votes
0 answers
99 views

Can we efficiently count modulo 2 the number of connected subgraphs of a planar graph?

Paper p.9 and Wikipedia relate the Tutte polynomial of a graph to another polynomial. If $(x-1)(y-1)=z$, $$T(G;x,y)=F_G(z,y)/H(G)$$ Where $F_G(z,y)=\sum_{A \subseteq E}z^{c(G_A)}(y-1)^{|A|} $ where …
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1 vote
1 answer
127 views

Reduction graph to planar bounded treewidth graph

We got reduction graph to planar bounded treewidth graph, but this is unlikely to be true. Let $H$, the planarizing gadget, be planar graph with four distinguished vertices $u,u',v,v'$ on the outer f …
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7 votes
0 answers
118 views

Contradicting claims about complexity of directed path graphs isomorphism

Thesis and a paper give conflicting claims about the complexity of graph isomorphism for directed path graphs. Since this means GI is polynomial likely I am missing something or there is something el …
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6 votes
2 answers
458 views

Is this a counterexample to a conjecture about independent domination in cartesian graph pro...

VIZING’S CONJECTURE: A SURVEY AND RECENT RESULTS (2009) by Bostjan Bresar , Paul Dorbec , Wayne Goddard , Bert L. Hartnell , Michael A. Henning , Sandi Klavzar , Douglas F. Rall p.25: Conjectu …
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