added remaining Witt graphs

src/sage/graphs/generators/distance_regular.pyx

@@ -399,7 +399,10 @@ def LargeWittGraph():
     The construction is taken from
     http://mathworld.wolfram.com/LargeWittGraph.html
 
-    EXAMPLES:
+    This is a distance-regular graph with intersection array
+    `[30,28,24;1,3,15]`.
+
+    EXAMPLES::
 
         sage: g = graphs.LargeWittGraph()
         sage: g.is_distance_regular(True)
@@ -419,3 +422,50 @@ def LargeWittGraph():
     W = Graph(edges, format='list_of_edges')
     W.name("Large Witt graph")
     return W
+
+def TruncatedWittGraph():
+    r"""
+    Return the truncated Witt graph.
+
+    This builds the large Witt graph, then removes
+    all vertices whose codeword start with a 1.
+
+    The graph is distance-regular with intersection array
+    `[15,14,12;1,1,9]`.
+
+    EXAMPLES::
+
+         sage: G = graphs.TruncatedWittGraph()
+         sage: G.is_distance_regular(True)
+         ([15, 14, 12, None], [None, 1, 1, 9])
+
+    """
+    # get large witt graph and remove all vertices which start with a 1
+    G = LargeWittGraph()
+    G.delete_vertices(filter(lambda x : x[0] == 1, G.vertices()))
+
+    G.name("Truncated Witt graph")
+    return G
+
+def DoublyTruncatedWittGraph():
+    r"""
+    Return the doubly truncated Witt graph.
+
+    This builds the truncated Witt graph, then removes
+    all vertices whose codeword start with a 1.
+
+    The graph is distance-regular with intersection array
+    `[7,6,4,4;1,1,1,6]`.
+
+    EXAMPLES::
+
+         sage: G = graphs.DoublyTruncatedWittGraph()
+         sage: G.is_distance_regular(True)
+         ([7, 6, 4, 4, None], [None, 1, 1, 1, 6])
+    """
+
+    G = TruncatedWittGraph()
+    G.delete_vertices(filter(lambda x : x[1] == 1, G.vertices()))
+
+    G.name("Doubly Truncated Witt graph")
+    return G

src/sage/graphs/graph_generators.py

@@ -110,6 +110,7 @@ def __append_to_doc(methods):
      "DesarguesGraph",
      "DejterGraph",
      "DoubleStarSnark",
+     "DoublyTruncatedWittGraph",
      "DurerGraph",
      "DyckGraph",
      "EllinghamHorton54Graph",
@@ -177,6 +178,7 @@ def __append_to_doc(methods):
      "TietzeGraph",
      "TruncatedIcosidodecahedralGraph",
      "TruncatedTetrahedralGraph",
+     "TruncatedWittGraph",
      "Tutte12Cage",
      "TutteCoxeterGraph",
      "TutteGraph",
@@ -1937,6 +1939,7 @@ def quadrangulations(self, order, minimum_degree=None, minimum_connectivity=None
     DejterGraph              = staticmethod(smallgraphs.DejterGraph)
     DesarguesGraph           = staticmethod(smallgraphs.DesarguesGraph)
     DoubleStarSnark          = staticmethod(smallgraphs.DoubleStarSnark)
+    DoublyTruncatedWittGraph = staticmethod(distance_regular.DoublyTruncatedWittGraph)
     DurerGraph               = staticmethod(smallgraphs.DurerGraph)
     DyckGraph                = staticmethod(smallgraphs.DyckGraph)
     EllinghamHorton54Graph   = staticmethod(smallgraphs.EllinghamHorton54Graph)
@@ -2005,7 +2008,8 @@ def quadrangulations(self, order, minimum_degree=None, minimum_connectivity=None
     TietzeGraph              = staticmethod(smallgraphs.TietzeGraph)
     Tutte12Cage              = staticmethod(smallgraphs.Tutte12Cage)
     TruncatedIcosidodecahedralGraph = staticmethod(smallgraphs.TruncatedIcosidodecahedralGraph)
-    TruncatedTetrahedralGraph= staticmethod(smallgraphs.TruncatedTetrahedralGraph)
+    TruncatedTetrahedralGraph = staticmethod(smallgraphs.TruncatedTetrahedralGraph)
+    TruncatedWittGraph       = staticmethod(distance_regular.TruncatedWittGraph)
     TutteCoxeterGraph        = staticmethod(smallgraphs.TutteCoxeterGraph)
     TutteGraph               = staticmethod(smallgraphs.TutteGraph)
     U42Graph216              = staticmethod(smallgraphs.U42Graph216)