Add Europe map graph

[jm58660]

This patch will add a graph that could be useful in some examples.

Unfortunately center() of Europe is quite large.

Component: graph theory

Author: Jori Mäntysalo

Branch/Commit: d053e63

Reviewer: David Coudert

Issue created by migration from https://trac.sagemath.org/ticket/24496

[jm58660]

Branch: u/jmantysalo/europe-map

[jm58660]

Commit: 3e0fcdc

[jm58660]

New commits:

3e0fcdc

Add map graph for Europe.

[dcoudert]

comment:3

You could do:

+    if continental:
+        G = G.subgraph(G.connected_component_containing_vertex('France'))
+        G.name(new="Continental Europe Map")
+    else:
+        G.add_vertices(no_land_border)
+        G.name(new="Europe Map")

Instead of France, you can of course choose another country ;)
The most important is to be independent of the order in which connected components are returned.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

d053e63

Minor modification.

[sagetrac-git]

Changed commit from 3e0fcdc to d053e63

[jm58660]

comment:5

As you wish. Actually "The list is ordered from largest to smallest component.", says documentation of connected_components, but it is not explicitly said in connected_components_subgraphs.

I select Austria as "central point". At least it will survive climate change and raising sea level...

[dcoudert]

comment:6

I checked that europe is a subgraph of the world (after removing Malta and Iceland that are added back to the world in #24488) !

[dcoudert]

Reviewer: David Coudert

[vbraun]

Changed branch from u/jmantysalo/europe-map to d053e63