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"""
Vitality measures.
"""
from functools import partial
import networkx as nx
__all__ = ["closeness_vitality"]
def closeness_vitality(G, node=None, weight=None, wiener_index=None):
"""Returns the closeness vitality for nodes in the graph.
The *closeness vitality* of a node, defined in Section 3.6.2 of [1],
is the change in the sum of distances between all node pairs when
excluding that node.
Parameters
----------
G : NetworkX graph
A strongly-connected graph.
weight : string
The name of the edge attribute used as weight. This is passed
directly to the :func:`~networkx.wiener_index` function.
node : object
If specified, only the closeness vitality for this node will be
returned. Otherwise, a dictionary mapping each node to its
closeness vitality will be returned.
Other parameters
----------------
wiener_index : number
If you have already computed the Wiener index of the graph
`G`, you can provide that value here. Otherwise, it will be
computed for you.
Returns
-------
dictionary or float
If `node` is None, this function returns a dictionary
with nodes as keys and closeness vitality as the
value. Otherwise, it returns only the closeness vitality for the
specified `node`.
The closeness vitality of a node may be negative infinity if
removing that node would disconnect the graph.
Examples
--------
>>> G = nx.cycle_graph(3)
>>> nx.closeness_vitality(G)
{0: 2.0, 1: 2.0, 2: 2.0}
See Also
--------
closeness_centrality
References
----------
.. [1] Ulrik Brandes, Thomas Erlebach (eds.).
*Network Analysis: Methodological Foundations*.
Springer, 2005.
<http://books.google.com/books?id=TTNhSm7HYrIC>
"""
if wiener_index is None:
wiener_index = nx.wiener_index(G, weight=weight)
if node is not None:
after = nx.wiener_index(G.subgraph(set(G) - {node}), weight=weight)
return wiener_index - after
vitality = partial(closeness_vitality, G, weight=weight, wiener_index=wiener_index)
# TODO This can be trivially parallelized.
return {v: vitality(node=v) for v in G}
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