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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.
1
vote
Bondy and Simonovits Proof for Small Graphs
That particular theorem is a "for all large enough $n$..." type result so I don't think it says much for small $n$. I'm not sure what would count as an equivalent formulation but it is interesting to …
3
votes
Minimal clique decompositions
Similar to Ben's answer is an octahedron which is $K_{2,2,2}$ and also $K_6$ minus a matching. There should be an enormous number of minimal covers for other complete multipartite graphs and for $K_{2 …
1
vote
Odd circles and doubly covered edges
Consider a triangular prism with $6$ vertices and $9$ edges. You need to pick two vertices from each triangle and that also chooses both ends of another edge. That is a problem if you view it as two …
4
votes
Accepted
What type of Hamming Graph is this?
Do you have all $k^n$ strings of length $n$ using your $k$ symbol alphabet or a selection such as all consecutive 30 letter strings found in the DNA of some individual. The former is a Hamming graph b …
3
votes
Accepted
Generalized graph products in view of vertex-transitive graphs
For the second question Will's example is to the point. Another description: start with a $k$-gon ($k \gt 3$ an odd prime) and decide that the obvious cyclic group will act transitively on the final g …
2
votes
Accepted
Symmetry preserving graph products
Revised answer (see previous version to make sense of comments):
The Petersen graph is a small wonderful and rather exceptional creature. It is not a paradigm.
Does this graph fit your construction …
4
votes
graphs that are intervals
What do you know about graphs with this property? I don't know any terminology which would be widely recognized. There is much terminology which can be utilized. to create a name.
A graph with this …
1
vote
Accepted
Matching in bipartite graphs
Is it a homework problem? (If so, it is a nice one and new to me.) So you need to rule out the existence of a set $A \subseteq X$ such that the set $B$ of all $y \in Y$ adjacent to some $a \in A$ has …
5
votes
Accepted
Is the following graph well known?
They might have a name, I don't know. For the next few lines let us call each a Partial Permutation graph $PP(n,k)$ (assume $k<n$). They may not get as much respect because they are not distance trans …
1
vote
Efficient computation of a vertex-partition for graphs
As you note, for a bipartite graph you get either the bipartition or the trivial partition (according as the number of spanning trees is even or odd). Any edge whose removal (keeping its endpoints) di …
1
vote
Lower bound on # spanning trees in a connected graph
I was going to guess something like what David found. But a reference certainly trumps a guess. Here is some heuristic reasoning. A connected graph of course has one spanning tree. You asked about us …
3
votes
How to find central vertex in a graph?
The question should be more specific. It depends what you know about the graph .
For a tree you can erase all degree 1 vertices then repeat on the new graph and stop when there are just one or two.
…
3
votes
Notation for a graph without any edges?
I suppose $n\cdot K_1$ assuming of course that $n \ge 1$. In the event that there are also no vertices it is sometimes called the Null Graph although F. Harary, F. and R. Read in "Is the Null Graph a …
4
votes
4-regular graph with every edge lying in a unique 4-cycle
There should be lots of these, even with the second condition. So many that I can't imagine a classification. I'll call a $4$-cycle a square.
One construction is as follows: Start with an appropriate …
1
vote
Accepted
Counting and constructing some special planar graphs
Consider this family of graphs which is very far from optimal but gives much more than you request: Let $n=3m+r$ and take a path of length $k=2m+r$ with vertices numbered in the obvious way and a pend …