Landmark.incidences

Landmark.incidences() → list[tuple[Vertex, Edge]]

Adjacent vertices paired with the edges that lead to them

Returns:

a (vertex, edge) pair for each edge leaving this vertex, in the order the edges were connected

Return type:

list of (Vertex subclass, Edge)

v.incidences() is adjacent and out_edges taken together: the first element of each pair is the vertex at the far end of the edge, the second is the edge itself, so its Edge.cost and Edge.data are at hand. It is equivalent to:

list(zip(v.adjacent(), v.out_edges()))

but is built in a single pass, which is what the path-planning methods want when they expand a vertex.

Note

• In graph-theory terms adjacent is a vertex’s adjacency list, out_edges its incidence list, and this is the two joined.

• For a directed graph the pairs are for the edges leaving this vertex. The ones entering it are in_edges, and the vertices at their tails are predecessors.

• There is one pair per edge, so parallel edges to the same vertex give repeated vertices with different edges, and an undirected self-loop gives the pair twice, once for each end.

>>> from pgraph import UGraph
>>> g = UGraph()
>>> v1 = g.add_vertex(coord=[0,0], name='v1')
>>> v2 = g.add_vertex(coord=[1,1], name='v2')
>>> v3 = g.add_vertex(coord=[2,2], name='v3')
>>> g.add_edge(v1, v2, cost=1.5)
Edge{[v1] -- [v2], cost=1.5}
>>> g.add_edge(v1, v3, cost=2.5)
Edge{[v1] -- [v3], cost=2.5}
>>> for vertex, edge in v1.incidences():
...     print(vertex.name, edge.cost)
v2 1.5
v3 2.5

Seealso:

adjacent isadjacent successors out_edges in_edges predecessors edgeto edges_to edges edgeto degree Graph.adjacency