node_boundary

node_boundary(G, nbunch1, nbunch2=None)

Returns the node boundary of nbunch1.

The node boundary of a set S with respect to a set T is the set of nodes v in T such that for some u in S, there is an edge joining u to v. If T is not specified, it is assumed to be the set of all nodes not in S.

Parameters:

GNetworkX graph

nbunch1iterable

Iterable of nodes in the graph representing the set of nodes whose node boundary will be returned. (This is the set S from the definition above.)

nbunch2iterable

Iterable of nodes representing the target (or “exterior”) set of nodes. (This is the set T from the definition above.) If not specified, this is assumed to be the set of all nodes in G not in nbunch1.

Returns:

set

The node boundary of nbunch1 with respect to nbunch2.

Notes

Any element of nbunch that is not in the graph G will be ignored.

nbunch1 and nbunch2 are usually meant to be disjoint, but in the interest of speed and generality, that is not required here.

Examples

>>> G = nx.wheel_graph(6)

When nbunch2=None:

>>> list(nx.node_boundary(G, (3, 4)))
[0, 2, 5]

When nbunch2 is given:

>>> list(nx.node_boundary(G, (3, 4), (0, 1, 5)))
[0, 5]