adding self loops related docs and tests for functions in cluster.py (

#7261)

* added self-loops notes

* added test_self_loops_square_clustering

* style fix

* style fix

networkx/algorithms/cluster.py

@@ -445,6 +445,10 @@ def transitivity(G):
     out : float
        Transitivity
 
+    Notes
+    -----
+    Self loops are ignored.
+
     Examples
     --------
     >>> G = nx.complete_graph(5)
@@ -581,6 +585,8 @@ def generalized_degree(G, nodes=None):
 
     Notes
     -----
+    Self loops are ignored.
+
     In a network of N nodes, the highest triangle multiplicity an edge can have
     is N-2.
 

networkx/algorithms/tests/test_cluster.py

@@ -457,6 +457,12 @@ def test_peng_square_clustering(self):
         G = nx.Graph([(1, 2), (1, 3), (2, 4), (3, 4), (3, 5), (3, 6)])
         assert nx.square_clustering(G, [1])[1] == 1 / 3
 
+    def test_self_loops_square_clustering(self):
+        G = nx.path_graph(5)
+        assert nx.square_clustering(G) == {0: 0, 1: 0.0, 2: 0.0, 3: 0.0, 4: 0}
+        G.add_edges_from([(0, 0), (1, 1), (2, 2)])
+        assert nx.square_clustering(G) == {0: 1, 1: 0.5, 2: 0.2, 3: 0.0, 4: 0}
+
 
 class TestAverageClustering:
     @classmethod