volume(G, S, weight=None)¶
Returns the volume of a set of nodes.
The volume of a set S is the sum of the (out-)degrees of nodes in S (taking into account parallel edges in multigraphs). 
G (NetworkX graph)
S (sequence) – A sequence of nodes in
weight (object) – Edge attribute key to use as weight. If not specified, edges have weight one.
The volume of the set of nodes represented by
Sin the graph
- Return type
David Gleich. Hierarchical Directed Spectral Graph Partitioning. <https://www.cs.purdue.edu/homes/dgleich/publications/Gleich%202005%20-%20hierarchical%20directed%20spectral.pdf>