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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.

3 votes

Efficient Hamiltonian cycle algorithms for graph classes

There are linear-time algorithms based on Whitney's and Tutte's theorems on 4-connected planar graphs: Asano, Takao, Shunji Kikuchi, and Nobuji Saito. "A linear algorithm for finding Hamiltonian cycl …
Martin Sleziak's user avatar
5 votes

determining k-edge-connectivity of a graph

Generally $k$-connectivity is computed using max-flow min-cut algorithms. I cannot quote you complexities off the top of my head, but you should be able to find the number of edges that disconnect an …
The Amplitwist's user avatar
5 votes

Higher-dimensional Fáry's theorem?

In the paper by Archdeacon et al., "Corollary 1.2 proves Grünbaum's conjecture for triangulations of the torus." Dan Archdeacon, C. Paul Bonnington, Joanna A. Ellis-Monaghan. "How to Exhibit Toroidal …
The Amplitwist's user avatar
4 votes

Can a 3-regular non-1-planar graph be constructed?

Did you check the Coxeter graph?
Joseph O'Rourke's user avatar
8 votes

Generalizations of the four-color theorem

There is a recent generalization to $k$-uniform hypergraphs that are embeddable in $\mathbb{R}^d$ without edge intersections. "For $k=d=2$ the problem specializes to graph planarity": Carl Georg Heis …
Martin Sleziak's user avatar
0 votes

Given the skeleton of an inscribed polytope. If I move the vertices so that no edge increase...

This addresses only the $n=m=2$ case. Break the polygon $P$ into an open polygonal chain with the same lengths as $P$. Place the chain in a large-radius circle, and shrink the radius until the chain c …
Joseph O'Rourke's user avatar
5 votes

How to find central vertex in a graph?

Mathematica has a function GraphCenter[] that computes the center of a graph (the set of vertices with minimum eccentricity--exactly your definition). You can find a description in the documentation h …
Martin Sleziak's user avatar
1 vote
Accepted

Surfaces generated by minimum-weight triangulations

My guess is that a minimum edge-weight triangulation would not in general lead to a minimum-area surface. Instead a minimum-area triangulation might. There is a considerable literature on triangulatio …
Joseph O'Rourke's user avatar
1 vote

Clustering of vertices in an $n$-dimensional cube

Just an illustration of @RichardKlitzing's construction in 3D:       His $n+1 = 4$ layers are: $$ v_1 \;,\; \{v_2,v_4,v_5\} \;,\; \{v_3,v_8,v_6\} \;,\; v_7 $$
Joseph O'Rourke's user avatar
2 votes
Accepted

Squaring a square and discrete Ricci flow

My question is answered in Lovász's book: Lovász, László. Graphs and Geometry. Vol. 65. American Mathematical Soc., 2019. p.82: Theorem 6.2. Every planar map in which the unbounded country is a qua …
Joseph O'Rourke's user avatar
2 votes

Squaring a square and discrete Ricci flow

I just found this citation, not cited in the AMS Notices paper (but I cannot yet access the Israel J Math paper itself): Schramm, Oded. "Square tilings with prescribed combinatorics." Israel Journal …
Joseph O'Rourke's user avatar
8 votes

Proofs of circle packing theorem

I can recommend Sariel Har-Peled's exposition in supplemental Chapter 15 of his book Geometric Approximation Algorithms. Ch15 PDF download. He emphasizes angles via a "whac-an-angle" game. He acknowle …
Joseph O'Rourke's user avatar
10 votes

Which curves and surfaces are realizable by linkages? references?

Erik Demaine and I also included a proof for $d=2$ in Geometric Folding Algorithms: Linkages, Origami, Polyhedra, Chapter 3. There we asked if there is a planar (non-crossing) linkage that "signs you …
Joseph O'Rourke's user avatar
10 votes

A tree with prime vertices

Not an answer, just a drawing of the tree including the OP's $2 \rightarrow 191$ path:          
Joseph O'Rourke's user avatar
5 votes
Accepted

Is the acyclic chromatic number bounded in terms of the book thickness?

I believe that "book thickness bounds the acyclic chromatic number" was established in this paper: Dujmovic, Vida, Attila Pór, and David R. Wood. "Track layouts of graphs." Discrete Mathematics an …
Joseph O'Rourke's user avatar

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