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## iof-tools / networkxMiCe / networkx-master / networkx / algorithms / tests / test_wiener.py @ 5cef0f13

 1 # test_wiener.py - unit tests for the wiener module  #  # Copyright 2015 NetworkX developers.  #  # This file is part of NetworkX.  #  # NetworkX is distributed under a BSD license; see LICENSE.txt for more  # information.  """Unit tests for the :mod:networkx.algorithms.wiener module."""  from __future__ import division  from nose.tools import eq_  from networkx import complete_graph  from networkx import DiGraph  from networkx import empty_graph  from networkx import path_graph  from networkx import wiener_index  class TestWienerIndex(object):   """Unit tests for computing the Wiener index of a graph."""   def test_disconnected_graph(self):   """Tests that the Wiener index of a disconnected graph is   positive infinity.     """   eq_(wiener_index(empty_graph(2)), float('inf'))   def test_directed(self):   """Tests that each pair of nodes in the directed graph is   counted once when computing the Wiener index.     """   G = complete_graph(3)   H = DiGraph(G)   eq_(2 * wiener_index(G), wiener_index(H))   def test_complete_graph(self):   """Tests that the Wiener index of the complete graph is simply   the number of edges.     """   n = 10   G = complete_graph(n)   eq_(wiener_index(G), n * (n - 1) / 2)   def test_path_graph(self):   """Tests that the Wiener index of the path graph is correctly   computed.     """   # In P_n, there are n - 1 pairs of vertices at distance one, n -   # 2 pairs at distance two, n - 3 at distance three, ..., 1 at   # distance n - 1, so the Wiener index should be   #   # 1 * (n - 1) + 2 * (n - 2) + ... + (n - 2) * 2 + (n - 1) * 1   #   # For example, in P_5,   #   # 1 * 4 + 2 * 3 + 3 * 2 + 4 * 1 = 2 (1 * 4 + 2 * 3)   #   # and in P_6,   #   # 1 * 5 + 2 * 4 + 3 * 3 + 4 * 2 + 5 * 1 = 2 (1 * 5 + 2 * 4) + 3 * 3   #   # assuming n is *odd*, this gives the formula   #   # 2 \sum_{i = 1}^{(n - 1) / 2} [i * (n - i)]   #   # assuming n is *even*, this gives the formula   #   # 2 \sum_{i = 1}^{n / 2} [i * (n - i)] - (n / 2) ** 2   #   n = 9   G = path_graph(n)   expected = 2 * sum(i * (n - i) for i in range(1, (n // 2) + 1))   actual = wiener_index(G)   eq_(expected, actual)