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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.

6 votes
Accepted

Connected graphs that are not 2 connected

See Kemkes, Graeme; Sato, Cristiane M.; Wormald, Nicholas, Asymptotic enumeration of sparse $2$-connected graphs, Random Struct. Algorithms 43, No. 3, 354–376 (2013). Zbl 1273.05127. PDF and referen …
The Amplitwist's user avatar
5 votes

Bounding number of k-cycles in a graph

Yes, this is addressed in the paper: Rivin, Igor, Counting cycles and finite dimensional (L^{p}) norms, Adv. Appl. Math. 29, No. 4, 647-662 (2002). ZBL1013.05042.
Igor Rivin's user avatar
  • 96.4k
1 vote

The matrix tree theorem for weighted graphs

A somewhat different take on weighted trees is taken in this paper: Jakobson, Dmitry; Rivin, Igor, Extremal metrics on graphs. I, Forum Math. 14, No. 1, 147-163 (2002). ZBL0995.05072. In particular, …
Igor Rivin's user avatar
  • 96.4k
3 votes

A generously vertex transitive graph which is not Cayley?

It seems that any distance-transitive graph satisfies your condition (of course, distance-transitivity is much stronger), and you can find many examples (both finite and infinite) in Peter Cameron's n …
Community's user avatar
  • 1
1 vote

Embedding a graph in $\mathbb{R}^3$ with partial geometric information

There are a number of papers by Mike Treacy (I. Rivin is a co-author on some) which address this problem, but in a purely practical manner, using essentially the scheme proposed by Bullet51. Here is o …
Igor Rivin's user avatar
  • 96.4k
7 votes
Accepted

Length minimizing graphs between a finite set of points

This is the so-called Steiner Tree Problem.
Igor Rivin's user avatar
  • 96.4k
6 votes

Laplacian of an infinite graph and connected components

As Uri Bader points out, the infinite tree has an infinitely dimensional space of harmonic functions, so this is an answer to the philosophical part of the question: The way you prove that all harmoni …
Igor Rivin's user avatar
  • 96.4k
10 votes
Accepted

When does a row standardized adjacency matrix have a real spectrum?

If the adjacency matrix is $A,$ the "row-standardized" matrix is $DA$, where $D$ is a diagonal matrix all of whose diagonal entries are positive, so has a positive diagonal square root $D^{1/2}$. Now, …
Rodrigo de Azevedo's user avatar
4 votes
Accepted

Generalisation of Kuratowski's theorem

I am not sure which direction gives you trouble, but the second condition is necessary, by the Moore-Young theorem, or a somewhat weaker version thereof, as discussed by Greg Kuperberg here. For the …
Piotr Hajlasz's user avatar
4 votes

How many non-homeomorphic surfaces arise from these graphs?

It sounds like you are trying to enumerate ribbon graphs, in which case you might want to look at: Do, Norman; Manescu, David, Quantum curves for the enumeration of ribbon graphs and hypermaps, Commu …
Martin Sleziak's user avatar
6 votes

Does there exist a notion of discrete riemannian metric on graph?

This circle of questions is studied in this old paper by D. Jakobson and I. Rivin.
Igor Rivin's user avatar
  • 96.4k
3 votes

Expected spectral radius for a sparse Erdős-Rényi binary matrix with a certain density

If you mean that $A$ is the adjacency matrix of an Erdos-Renyi random graph, then the question has been studied, and your conjecture is false (but just barely). See Krivelevich, Michael; Sudakov, Ben …
Igor Rivin's user avatar
  • 96.4k
14 votes

A random walk on an infinite graph is recurrent iff ...?

This is a huge subject, but the best introductory reference remains: Doyle, Peter G.; Snell, J.Laurie, Random walks and electric networks, The Carus Mathematical Monographs, 22. Washington, D. C.: Th …
Igor Rivin's user avatar
  • 96.4k
1 vote
Accepted

References studying properties of a graph which are stable under finite perturbation

The references for these can be found in Doyle and Snell's deathless classic (which is available for free on arXiv.org. ). Section 2.4 is particularly a propos. Doyle, Peter G.; Snell, J.Laurie, Rand …
Igor Rivin's user avatar
  • 96.4k
2 votes

Number of non-equivalent graph embeddings

Peter Heinig's answer is excellent, but here are some further remarks: Under the "ambient isotopy" definition, there are infinitely many classes of embeddings (because the mapping class group is inf …
Igor Rivin's user avatar
  • 96.4k

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