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Problems related to graph drawing such as crossing numbers, layout designs, and intersection graphs.

5 votes
2 answers
249 views

Finding a special plane graph with some requirements on the faces

Is there a plane graph such that (1) the outer face has degree 3, i.e, is a triangle, (2) every inner face has degree 5, and (3) any two degree 5 faces share at most one commong edge.
Xin Zhang's user avatar
  • 1,190
4 votes
0 answers
129 views

What is the crossing number of dodecahedron with a copy of $K_5$ inside each face

Suppose we are given a regular dodecahedron. Then we add five crossed edges inside each of its faces (actually, inside each face it is a copy of $K_5$). It is clear that this drawing has 60 crossings. …
Xin Zhang's user avatar
  • 1,190
3 votes
1 answer
196 views

Looking for examples showing that the crossing number may not be realized by the drawings wi...

The crossing number $cr(G)$ of a graph $G$ is the lowest number of edge crossings of a plane drawing of the graph $G$. The local crossing number of a drawing of a graph is the largest number of crossi …
Xin Zhang's user avatar
  • 1,190
6 votes
2 answers
289 views

Is there any maximal 1-planar or 2-planar graph that is not 3-connected

A graph is $k$-planar if it can be drawn in the plane so that each edge is crossed at most $k$ times. A $k$-planar graph $G$ is maximal if $G+uv$ is not $k$-planar for any non-adjacent vertices $u,v\i …
Xin Zhang's user avatar
  • 1,190
5 votes
1 answer
260 views

What is the crossing number of cube with a pair of crossing edges inside each face

Suppose we are given a cube and we add a pair of crossing edges inside each of its faces. It is clear that this drawing has 6 crossings. My question is whether such a graph has crossing number 6? How …
Xin Zhang's user avatar
  • 1,190
3 votes
Accepted

Is there any maximal 1-planar or 2-planar graph that is not 3-connected

This is a non-3-connected 1-planar example...
Xin Zhang's user avatar
  • 1,190
1 vote
1 answer
87 views

Is there any known upper bound for the local crossing number of a graph drawing in the plane?

The local crossing number ${\rm LCR(G)}$ of a graph $G$ is defined as the least nonnegative integer $k$ such that the graph has a $k$-planar drawing. In other words, it is the smallest possible number …
Xin Zhang's user avatar
  • 1,190
7 votes
2 answers
251 views

There is a 3-connected 5-regular simple $n$-vertex planar graph iff $n$ satisfies....?

Is there any characterization on the set of integers $n$ such that there is a 3-connected 5-regular simple $n$-vertex planar graph?
Xin Zhang's user avatar
  • 1,190
2 votes
1 answer
127 views

The density of a tripartite 1-planar graph

1-planar graphs are those can be drawn in the plane so that there is at most one crossing per edge. We know that the maximum number of edges of an $n$-vertex 1-planar graph is at most $4n-8$, and the …
Xin Zhang's user avatar
  • 1,190
1 vote
Accepted

The density of a tripartite 1-planar graph

I find the following source. The known bound is 3.5n-7 (Theorem 4.8, pp. 57). https://www.springer.com/gp/book/9789811565328 Beyond Planar Graphs Communications of NII Shonan Meetings Editors: Hong, S …
Xin Zhang's user avatar
  • 1,190
0 votes
0 answers
80 views

Is there is a constant $c$ such that toroidal graphs are minor-$c$-colorable?

A toroidal graph is a graph that can be embedded on a torus. In other words, the graph's vertices can be placed on a torus such that no edges cross. A minor of graph G is a graph obtained from G by me …
Xin Zhang's user avatar
  • 1,190
4 votes

Is it possible that every edge in a 1-planar drawing with minimum number of crossings is cro...

Concerning the above answer, I do not quite agree with the last sentence. Why is there some vertex of $D^\times$ outside $O$ if $y$ is a dummy vertex on $C$? I draw a figure, where $y$ is a dummy vert …
Xin Zhang's user avatar
  • 1,190