Why Networkx Output for Betweenness Centrality is wrong?

Question

I want to calculate betweenness for a simple graph with 6 nodes:

G=nx.Graph()
e=[(1,2),(1,5),(2,3),(3,6),(5,6),(4,2),(4,3)]
G.add_edges_from(e)
btw=nx.betweenness_centrality(G)

As I calculated for each node the output should be:

{1: 1.5, 2: 2.5, 5: 1, 3: 2.5, 6: 1.5, 4: 0}

But the output is :

{1: 0.15000000000000002,
 2: 0.25,
 5: 0.1,
 3: 0.25,
 6: 0.15000000000000002,
 4: 0.0} 

What is the reason?

Answer 1

It seems you're calculating the non-normalized centrality, whereas by default betweenness_centrality has normalized set to True.

Instead set it to False:

G=nx.Graph()
e=[(1,2),(1,5),(2,3),(3,6),(5,6),(4,2),(4,3)]
G.add_edges_from(e)
btw=nx.betweenness_centrality(G, normalized=False)
# {1: 1.5, 2: 2.5, 5: 1.0, 3: 2.5, 6: 1.5, 4: 0.0}