What is an attracting component subgraph?

What is a attracting component subgraph of a graph?

Networkx has an algorithm for this. But I am unable to understand what this is because:

>>> g.edges()
开发者_如何学Go[(0, 1), (1, 2), (2, 3), (2, 5), (3, 4)]
>>> for l in nx.algorithms.components.attracting.attracting_component_subgraphs(g):
...     print l.edges()
...     print l.nodes()
... 
[]
[4]
[]
[5]

The definition of an attracting component is provided in the documentation for nx.algorithms.components.attracting_components.

An attracting component in a directed graph is a strongly connected component with the property that a random walker on the graph will never leave the component, once it enters the component.

The nodes in attracting components can also be thought of as recurrent nodes. If a random walker enters the attractor containing the node, then the node will be visited infinitely often.

http://networkx.lanl.gov/reference/generated/networkx.algorithms.components.attracting.attracting_components.html#networkx.algorithms.components.attracting.attracting_components

Thus, an attracting component subgraph would be a list of nodes that induce subgraphs meeting this definition.