Empire Problem
Author
Eric W. Weisstein
Title
Empire Problem
Description
The empire problem, also known as the m-pire problem) asks for the maximum number of colors needed to color countries such that no two countries sharing a common border have the same color (this is the usual four-color theorem) in the case where each country consists of m disjoint regions. Heawood (1890) showed that 6m colors are sufficient, and for the case m=2, 12 colors are also necessary (Gardner 1997; Frederickson 2002, pp. 31-32).
Category
Educational Materials
Keywords
URL
http://www.notebookarchive.org/2019-07-0z3vtr2/
DOI
https://notebookarchive.org/2019-07-0z3vtr2
Date Added
2019-07-02
Date Last Modified
2019-07-02
File Size
0.83 megabytes
Supplements
Rights
Redistribution rights reserved
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Empire Problem
Empire Problem
Author
Author
Eric W. Weisstein
August 2, 2018
August 2, 2018
©2018 Wolfram Research, Inc. except for portions noted otherwise
m=2
m=2
By Scott Kim via Ed Pegg, Aug 2 2018
A triangulated planar graph on 24 points.
In[]:=
TwopireEdges={{1,3},{1,10},{1,11},{1,12},{1,17},{1,18},{1,20},{2,3},{2,5},{2,6},{2,10},{2,19},{2,23},{2,24},{3,5},{3,12},{3,19},{3,20},{3,22},{4,5},{4,7},{4,8},{4,12},{4,13},{4,14},{4,21},{5,7},{5,21},{5,22},{5,23},{6,7},{6,9},{6,10},{6,15},{6,16},{6,24},{7,9},{7,13},{7,23},{7,24},{8,9},{8,11},{8,12},{8,14},{8,17},{8,18},{9,11},{9,13},{9,14},{9,15},{10,11},{10,16},{10,19},{10,20},{11,15},{11,16},{11,18},{12,17},{12,21},{12,22},{13,14},{15,16},{17,18},{19,20},{21,22},{23,24}};
In[]:=
{g=System`Graph[Range[Max[Flatten[TwopireEdges]]],UndirectedEdge@@@TwopireEdges],g2=System`Graph[Range[Max[Flatten[TwopireEdges]]],UndirectedEdge@@@TwopireEdges,GraphLayout"PlanarEmbedding"],g3=System`Graph[Range[Max[Flatten[TwopireEdges]]],UndirectedEdge@@@TwopireEdges,GraphLayout"TutteEmbedding"],g4=PlanarGraph[g]}
Out[]=
,
,
,
In[]:=
{TriangulatedGraphQ[g],PlanarGraphQ[g]}
Out[]=
{True,True}
When points 1-12 are paired with 13-24 a 12-color 2-pire results.
Complement[Subsets[Range[12],{2}],Sort[Sort/@Mod[TwopireEdges,12,1]]]
Out[]=
{}
In[]:=
gg=System`Graph[Range[Max[Flatten[TwopireEdges]]],UndirectedEdge@@@TwopireEdges,GraphLayout"PlanarEmbedding",VertexLabels"Name"]
Out[]=
In[]:=
faces=FindFace[gg]
Out[]=
{{1,3,12},{1,3,20},{1,10,11},{1,10,20},{1,11,18},{1,12,17},{1,17,18},{2,3,5},{2,3,19},{2,5,23},{2,6,10},{2,6,24},{2,10,19},{2,23,24},{3,5,22},{3,12,22},{3,19,20},{4,5,7},{4,5,21},{4,7,13},{4,8,12},{4,8,14},{4,12,21},{4,13,14},{5,7,23},{5,21,22},{6,7,9},{6,7,24},{6,9,15},{6,10,16},{6,15,16},{7,9,13},{7,23,24},{8,9,11},{8,9,14},{8,11,18},{8,12,17},{8,17,18},{9,11,15},{9,13,14},{10,11,16},{10,19,20},{11,15,16},{12,21,22}}
GraphData
GraphData
GraphDataString
GraphDataString
In[]:=
file=OpenWrite["~/twopire.m"]
Out[]=
OutputStream
|
WriteString[file,GraphDataString[
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Cite this as: Eric W. Weisstein, "Empire Problem" from the Notebook Archive (2018), https://notebookarchive.org/2019-07-0z3vtr2
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