betweenness_centrality_subset#

betweenness_centrality_subset(G, sources, targets, normalized=False, weight=None)[source]#

Compute betweenness centrality for a subset of nodes.

\[c_B(v) = \sum_{s \in S, t \in T} \frac{\sigma(s, t | v)}{\sigma(s, t)}\]

where \(S\) is the set of sources, \(T\) is the set of targets, \(\sigma(s, t)\) is the number of shortest \((s, t)\)-paths, and \(\sigma(s, t | v)\) is the number of those paths passing through some node \(v\) other than \(s\) and \(t\). If \(s = t\), \(\sigma(s, t) = 1\), and if \(v \in \{s, t\}\), \(\sigma(s, t | v) = 0\) [2]. The denominator \(\sigma(s, t)\) is a normalization factor that can be turned off to get the raw path counts.

Parameters:
Ggraph

A NetworkX graph.

sources: list of nodes

Nodes to use as sources for shortest paths in betweenness.

targets: list of nodes

Nodes to use as targets for shortest paths in betweenness.

normalizedbool, optional (default=False)

If True, the betweenness values are rescaled by dividing by the number of possible \((s, t)\)-pairs in the graph.

weightNone or string, optional (default=None)

If None, all edge weights are 1. Otherwise holds the name of the edge attribute used as weight. Weights are used to calculate weighted shortest paths, so they are interpreted as distances.

Returns:
nodesdict

Dictionary of nodes with betweenness centrality as the value.

Notes

The basic algorithm is from [1].

For weighted graphs the edge weights must be greater than zero. Zero edge weights can produce an infinite number of equal length paths between pairs of nodes.

The normalization might seem a little strange but it is designed to make betweenness_centrality(G) be the same as betweenness_centrality_subset(G,sources=G.nodes(),targets=G.nodes()).

The total number of paths between source and target is counted differently for directed and undirected graphs. Directed paths are easy to count. Undirected paths are tricky: should a path from u to v count as 1 undirected path or as 2 directed paths? We are only counting the paths in one direction. They are undirected paths but we are counting them in a directed way. To count them as undirected paths, each should count as half a path.

References

[1]

Ulrik Brandes, A Faster Algorithm for Betweenness Centrality. Journal of Mathematical Sociology 25(2):163-177, 2001. https://doi.org/10.1080/0022250X.2001.9990249

[2]

Ulrik Brandes: On Variants of Shortest-Path Betweenness Centrality and their Generic Computation. Social Networks 30(2):136-145, 2008. https://doi.org/10.1016/j.socnet.2007.11.001