The ContractSubgraph command returns a new graph with all the vertices in S merged into a single vertex. The neighborhood of the new vertex will be the union of the neighborhoods of all of merged vertices.

If S is given as a subgraph of G, all the vertices of S will be contracted.

To contract a single edge, use the Contract command.

$\mathrm{with}\left(\mathrm{GraphTheory}\right)\:$

$\mathrm{C6}≔\mathrm{CycleGraph}\left(6\right)$

$\mathrm{C6}≔\mathrm{Graph\; 1:\; an\; undirected\; graph\; with\; 6\; vertices\; and\; 6\; edges}$

$H≔\mathrm{ContractSubgraph}\left(\mathrm{C6}\,\left[1\,2\,6\right]\right)$

$H≔\mathrm{Graph\; 2:\; an\; undirected\; graph\; with\; 4\; vertices\; and\; 4\; edges}$

$\mathrm{Vertices}\left(H\right)$

$\left[1\,3\,4\,5\right]$

$\mathrm{Edges}\left(H\right)$

$\left\{\left\{1\,3\right\}\,\left\{1\,5\right\}\,\left\{3\,4\right\}\,\left\{4\,5\right\}\right\}$

$\mathrm{with}\left(\mathrm{SpecialGraphs}\right)\:$

$P≔\mathrm{PetersenGraph}\left(\right)$

$P≔\mathrm{Graph\; 3:\; an\; undirected\; graph\; with\; 10\; vertices\; and\; 15\; edges}$

$\mathrm{DrawGraph}\left(P\right)$

$H≔\mathrm{ContractSubgraph}\left(P\,\left[1\,2\,3\,6\,7\,9\right]\right)$

$H≔\mathrm{Graph\; 4:\; an\; undirected\; graph\; with\; 5\; vertices\; and\; 7\; edges}$

$\mathrm{DrawGraph}\left(H\right)$

The GraphTheory[ContractSubgraph] command was introduced in Maple 2020.

For more information on Maple 2020 changes, see Updates in Maple 2020.