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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.

4 votes

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

Did you check the Coxeter graph?
Joseph O'Rourke'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
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 …
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 …
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
2 votes
Accepted

Uniqueness constraints for Delaunay triangulation

I think it is well-understood that "no four points cocircular" avoids Delaunay triangulation degeneracies. It is also well-understood that one can have four cocircular points that don't cause any dege …
Joseph O'Rourke's user avatar
7 votes
Accepted

Convex triangulations

Nice idea but it seems not to always exist:                     Point $4$'s star is reflex at $3$, Point $3$'s star is reflex at $4$. Here's an argument that those are the only two triangulati …
Joseph O'Rourke's user avatar
2 votes

Polygonal paths and polygons with prescribed set of vertices

This paper addresses similar (but I don't think identical) questions. In any case, a key search phrase is covering path. Dumitrescu, Adrian, Dániel Gerbner, Balázs Keszegh, and Csaba D. Tóth. "Cov …
Joseph O'Rourke's user avatar
4 votes

Polygonal paths and polygons with prescribed set of vertices

Not an answer, just an illustration for $6$ points, $0 \le x+y \le 2$.       $A,B,C$: Point $3$ cannot connect to $1$ or $6$, so it must connect to $2,5$ or $4,5$ or $2,4$. $B$: Point $6$ is now …
Joseph O'Rourke's user avatar
2 votes
Accepted

Relation between vertex connectivity and independent set

Addressing just this: "Given a graph 𝐺 does there exist any command in SageMath or in any other software which can say the minimum separating set of a graph?" This set is known as a minimum ve …
Joseph O'Rourke's user avatar

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