edge_expansion(G, S, T=None, weight=None)¶
Returns the edge expansion between two node sets.
The edge expansion is the quotient of the cut size and the smaller of the cardinalities of the two sets. 
- G (NetworkX graph)
- S (sequence) – A sequence of nodes in
- T (sequence) – A sequence of nodes in
- weight (object) – Edge attribute key to use as weight. If not specified, edges have weight one.
The edge expansion between the two sets
 Fan Chung. Spectral Graph Theory. (CBMS Regional Conference Series in Mathematics, No. 92), American Mathematical Society, 1997, ISBN 0-8218-0315-8 <http://www.math.ucsd.edu/~fan/research/revised.html>