R/data_ison.R
ison_koenigsberg.RdThe Seven Bridges of Koenigsberg is a notable historical problem in mathematics and laid the foundations of graph theory. The city of Koenigsberg in Prussia (now Kaliningrad, Russia) was set on both sides of the Pregel River, and included two large islands which were connected to each other and the mainland by seven bridges. A weekend diversion for inhabitants was to find a walk through the city that would cross each bridge once and only once. The islands could not be reached by any route other than the bridges, and every bridge must have been crossed completely every time (one could not walk half way onto the bridge and then turn around and later cross the other half from the other side). In 1735, Leonard Euler proved that the problem has no solution.
data(ison_koenigsberg)#> # A labelled, undirected network of 4 nodes and 7 ties
#> # A tibble: 4 x 3
#> name lat lon
#> <chr> <dbl> <dbl>
#> 1 Altstadt 54.7 20.5
#> 2 Kneiphof 54.7 20.5
#> 3 Lomse 54.7 20.5
#> 4 Vorstadt 54.7 20.5
#> # A tibble: 7 x 3
#> from to name
#> <int> <int> <chr>
#> 1 1 2 Kraemer Bruecke
#> 2 1 2 Schmiedebruecke
#> 3 1 3 Holzbruecke
#> 4 2 3 Honigbruecke
#> 5 2 4 Gruene Bruecke
#> 6 2 4 Koettelbruecke
#> # i 1 more row{igraphdata}
Euler, Leonard. 1741. “Solutio problematis ad geometriam situs pertinentis.” Commentarii academiae scientiarum Petropolitanae.