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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.

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
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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
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 …
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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, …
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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 …
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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.
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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 …
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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 …
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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 …
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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 …
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1 vote

Lower bound on diameter of trivalent graphs

To amplify on Fedor's answer, random graphs come close to this bound, for a lot more color see the ancient (but still useful) 1987 paper by Fan Chung.
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2 votes

Voronoi and Delaunay

This question is much too broad. However, a good introduction (to various generalizations, as well) is in Edelsbrunner's little book. Edelsbrunner, Herbert, Geometry and topology for mesh generation. …
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4 votes

Applications of Kirchhoff's circuit laws to graph theory

The canonical reference on all thinks Kirckhoffian is Doyle, Peter G.; Snell, J.Laurie, Random walks and electric networks, The Carus Mathematical Monographs, 22. Washington, D. C.: The Mathematical …
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