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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

Chromatic number of graphs of tangent closed balls

I find a paper of Hiroshi Maehara (http://link.springer.com/article/10.1007%2Fs00373-007-0702-7). He studies packing of a) closed balls, b) balls on a table, c) unit balls, d) unit balls within a rest …
Hao Chen's user avatar
  • 2,581
4 votes
0 answers
169 views

Graph drawing maximizing the volume of the convex hull

Given a graph $G=(V,E)$ and a length function $\ell:E\to\mathbb{R}_+$. An embedding of the graph into the $d$-dimensional Euclidean space is a map $f:V\to\mathbb{R}^d$ such that $||f(u)-f(v)||=\ell(uv …
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2 votes

Graphs with dangling edges

Such graphs were used in differential geometry to describe the gluing construction. See Kapouleas, Nicolaos, Complete constant mean curvature surfaces in Euclidean three-space, Ann. Math. (2) 131, No …
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13 votes

Chromatic number of graphs of tangent closed balls

Update May 2016 I removed the updates in Oct 2015. I was trying to combine two copies of strongly regular ball packings to double the chromatic number. But it has been point out that my constructio …
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7 votes
2 answers
178 views

Graph embedding that locally minimizes total edge lengths

I consider a graph $G$ (possibly infinite, but locally finite) embedded in the Euclidean plane $\mathbb{E}^2 \cup \{\infty\}$ such that each local perturbation of the embedding "increases the total le …
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1 vote

Graph embedding that locally minimizes total edge lengths

Finally, I find that the works of Ivanov and Tuzhilin seem to be very close to what I'm looking for.
Hao Chen's user avatar
  • 2,581
6 votes
1 answer
570 views

How does the distribution of Erdős number evolve over time ? How to build a model to fit the...

Let $E(n,t)$ be the number of mathematicians with finite positive Erdős number $n$ at time $t$. As old mathematicians leave, and new mathematicians come, how does $E(n,t)$ change over time ? We can …
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11 votes
1 answer
366 views

What is known about the chromatic number for minimum-distance graphs in higher dimensions?

For a set of points in $\mathbb{R}^d$ with minimum distance $a$, the minimum-distance graph connect two points iff they are at distance $a$. We can also view it as the tangency graph for a set of uni …
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32 votes

Generalizations of the four-color theorem

The coloring of higher dimensional ball packings. A ball packing is a collection of balls with disjoint interiors. The tangency graph of a ball packing takes the balls as vertices and connect two v …
17 votes
Accepted

Koebe–Andreev–Thurston theorem - where can I find a proof?

There are many proofs, and I'm not claiming that the following list is complete. New references are welcome. (First proof) Paul Koebe, Kontaktprobleme der konformen Abbildung, Ber. Verh. Sächs. Ak …
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