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    Node centrality
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Loads a directed graph and computes the following node centrality measures.

Measures defined on a undirected graph (we drop edge directions):
  -- degree centrality
  -- closeness centrality
  -- betweenness centrality
  -- eigenvector centrality
Measures defined on (the original) directed graph
  -- page rank
  -- hubs and authorities

For more details on defitions of these measures see 
http://en.wikipedia.org/wiki/Centrality

The code works under Windows with Visual Studio or Cygwin with GCC,
Mac OS X, Linux and other Unix variants with GCC. Make sure that a
C++ compiler is installed on the system. Visual Studio project files
and makefiles are provided. For makefiles, compile the code with
"make all".

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Parameters:

   -i:Input graph (tab separated list of edges) (default:'graph.txt')
   -o:Output file name (default:'node_centrality.txt')

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Usage:

Compute centralities of the nodes in the AS graph:

centrality -i:../as20graph.txt
