Add regular_bipartite_graphs

graphillion/graphset.py

@@ -2422,8 +2422,10 @@ def regular_graphs(degree=None, is_connected=True, graphset=None):
         if degree == None:
             degree = (1, len(GraphSet._vertices))
 
+        ss = None if graphset is None else graphset._ss
+
         ss = _graphillion._regular_graphs(graph=graph,
-                                          degree=degree, is_connected=is_connected,graphset=graphset)
+                                          degree=degree, is_connected=is_connected,graphset=ss)
         return GraphSet(ss)
 
     @staticmethod
@@ -2537,6 +2539,41 @@ def bipartite_graphs(graphset=None):
 
         return graphset.non_supergraphs(odd_cycle_gs)
 
+    @staticmethod
+    def regular_bipartite_graphs(degree=None, is_connected=True, graphset=None):
+        """Returns a GraphSet of regular bipartite subgraphs.
+
+        Example:
+          >>> GraphSet.regular_bipartite_graphs()
+
+          # The degree is 3 and the graphs are not necessarily connected.
+          >>> GraphSet.regular_graphs(3, False)
+
+          # The degree is at least 2 and at most 5, and
+          # the graphs are connected.
+          >>> GraphSet.regular_graphs((2, 5), True)
+
+        Args:
+          degree: Tuple or Integer. If it is a tuple (l, u),
+            the degree is at least l and at most u.
+            If it is an integer d, the degree is d.
+            If it is None, the degree is arbitrary.
+          is_connected: Bool. If it is True, the graphs are
+            connected. If it is False, the graphs are
+            not necessarily connected.
+          graphset: Optional. A GraphSet object. Subgraphs to be stored
+            are selected from this object.
+
+        Returns:
+          A new GraphSet object.
+  
+        See Also:
+          regular_graphs()
+          bipartite_graphs()
+        """
+        bi_graphs = GraphSet.bipartite_graphs(graphset=graphset)
+        return GraphSet.regular_graphs(degree=degree, is_connected=is_connected, graphset=bi_graphs)
+
     @staticmethod
     def show_messages(flag=True):
         """Enables/disables status messages.

graphillion/test/graphset.py

@@ -430,6 +430,22 @@ def test_regular_graphs(self):
         self.assertTrue([(2, 4), (2, 5), (3, 4), (3, 5)] in gs)
         self.assertTrue([(1, 2)] not in gs)
 
+    def test_regular_bipartite_graphs(self):
+        GraphSet.set_universe([(1, 2), (1, 4), (1, 5), (2, 3), (2, 5),
+                               (3, 6), (4, 5), (5, 6)])
+
+        gs = GraphSet.regular_bipartite_graphs(is_connected=False)
+        self.assertEqual(len(gs), 27)
+        self.assertTrue([(1, 2), (1, 4), (2, 3), (3, 6), (4, 5), (5, 6)] in gs)
+        self.assertTrue([(1, 4), (2, 5), (3, 6)] in gs)
+        self.assertTrue([(1, 2), (1, 5), (2, 3), (3, 6), (5, 6)] not in gs)
+
+        gs = GraphSet.regular_bipartite_graphs(is_connected=True)
+        self.assertEqual(len(gs), 11)
+        self.assertTrue([(1, 2), (1, 4), (2, 3), (3, 6), (4, 5), (5, 6)] in gs)
+        self.assertTrue([(1, 4), (2, 5), (3, 6)] not in gs)
+        self.assertTrue([(1, 2), (1, 5), (2, 3), (3, 6), (5, 6)] not in gs)
+
     def test_partitions(self):
         GraphSet.set_universe([(1, 2), (1, 4), (2, 3), (2, 5), (3, 6), (4, 5),
                                (5, 6)])