diff env/lib/python3.9/site-packages/networkx/algorithms/tests/test_wiener.py @ 0:4f3585e2f14b draft default tip

"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.9/site-packages/networkx/algorithms/tests/test_wiener.py	Mon Mar 22 18:12:50 2021 +0000
@@ -0,0 +1,70 @@
+"""Unit tests for the :mod:`networkx.algorithms.wiener` module."""
+
+
+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:
+    """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.
+
+        """
+        assert 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)
+        assert (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)
+        assert 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)
+        assert expected == actual