trac #15623: Immutable graph backend for Posets

src/sage/combinat/posets/hasse_diagram.py

@@ -46,11 +46,6 @@ class HasseDiagram(DiGraph):
         Hasse diagram of a poset containing 4 elements
         sage: TestSuite(H).run()
     """
-
-    # Hasse diagrams are immutable. This temporary hack enables the
-    # __hash__ method of DiGraph
-    _immutable = True
-
     def _repr_(self):
         r"""
         TESTS::

src/sage/combinat/posets/posets.py

@@ -740,7 +740,7 @@ def __classcall__(cls, hasse_diagram, elements = None, category = None, facade =
                 facade = hasse_diagram in Sets().Facades()
             hasse_diagram = hasse_diagram._hasse_diagram
         else:
-            hasse_diagram = HasseDiagram(hasse_diagram)
+            hasse_diagram = HasseDiagram(hasse_diagram, data_structure="static_sparse")
             if elements is None:
                 elements = hasse_diagram.vertices()
             if facade is None:
@@ -1490,7 +1490,6 @@ def to_graph(self):
         """
         from sage.graphs.graph import Graph
         G = Graph(self.hasse_diagram())
-        G._immutable = True
         return G
 
     def level_sets(self):

src/sage/graphs/base/static_sparse_backend.pyx

@@ -40,6 +40,7 @@ from sage.graphs.base.static_sparse_graph cimport (init_short_digraph,
 from c_graph import CGraphBackend
 from sage.misc.bitset cimport FrozenBitset
 from libc.stdint cimport uint32_t
+include 'sage/misc/bitset.pxi'
 
 cdef class StaticSparseCGraph(CGraph):
     """
@@ -64,10 +65,14 @@ cdef class StaticSparseCGraph(CGraph):
         has_labels = any(not l is None for _,_,l in G.edge_iterator())
         self.directed = G.is_directed()
 
-        init_short_digraph(self.g,G, edge_labelled = has_labels)
+        init_short_digraph(self.g, G, edge_labelled = has_labels)
         if self.directed:
             init_reverse(self.g_rev,self.g)
 
+        # Defining the meaningless set of 'active' vertices. Because of CGraph.
+        bitset_init(self.active_vertices,  self.g.n+1)
+        bitset_set_first_n(self.active_vertices, self.g.n)
+
     def __dealloc__(self):
         r"""
         Freeing the memory
@@ -77,6 +82,7 @@ cdef class StaticSparseCGraph(CGraph):
             sage: from sage.graphs.base.static_sparse_backend import StaticSparseCGraph
             sage: g = StaticSparseCGraph(graphs.PetersenGraph())
         """
+        bitset_free(self.active_vertices)
         free_short_digraph(self.g)
         if self.g_rev != NULL:
             free_short_digraph(self.g_rev)
@@ -361,7 +367,9 @@ class StaticSparseBackend(CGraphBackend):
         """
         cdef StaticSparseCGraph cg = <StaticSparseCGraph> StaticSparseCGraph(G)
         self._cg = cg
-        self._directed = cg.directed
+
+        # .directed and not ._directed. Because of CGraph.
+        self.directed = cg.directed
 
         vertices = G.vertices()
         self._order = len(vertices)
@@ -374,6 +382,12 @@ class StaticSparseBackend(CGraphBackend):
         self._vertex_to_labels = vertices
         self._vertex_to_int = {v:i for i,v in enumerate(vertices)}
 
+        # Needed by CGraph. The first one is just an alias, and the second is
+        # useless : accessing _vertex_to_labels (which is a list) is faster than
+        # vertex_labels (which is a dictionary)
+        self.vertex_ints = self._vertex_to_int
+        self.vertex_labels = {i:v for i,v in enumerate(vertices)}
+
     def __reduce__(self):
         """
         Return a tuple used for pickling this graph.
@@ -383,7 +397,7 @@ class StaticSparseBackend(CGraphBackend):
             sage: G = Graph(graphs.PetersenGraph(), immutable=True)
             sage: _ = loads(dumps(G))
         """
-        if self._directed:
+        if self.directed:
             from sage.graphs.digraph import DiGraph as constructor
         else:
             from sage.graphs.graph import Graph as constructor
@@ -556,6 +570,13 @@ class StaticSparseBackend(CGraphBackend):
             [(0, 1), (0, 4), (0, 5)]
             sage: list(g.iterator_in_edges([0],True))
             [(0, 1, None), (0, 4, None), (0, 5, None)]
+
+        ::
+
+            sage: DiGraph(digraphs.Path(5),immutable=False).incoming_edges([2])
+            [(1, 2, None)]
+            sage: DiGraph(digraphs.Path(5),immutable=True).incoming_edges([2])
+            [(1, 2, None)]
         """
         cdef StaticSparseCGraph cg = self._cg
         if not cg.directed:
@@ -573,11 +594,11 @@ class StaticSparseBackend(CGraphBackend):
             vi = self._vertex_to_labels[i]
             for j in range(out_degree(cg.g_rev,i)):
                 if labels:
-                    yield (vi,
-                           self._vertex_to_labels[cg.g_rev.neighbors[i][j]],
+                    yield (self._vertex_to_labels[cg.g_rev.neighbors[i][j]],
+                           vi,
                            edge_label(cg.g_rev,cg.g_rev.neighbors[i]+j))
                 else:
-                    yield vi,self._vertex_to_labels[cg.g_rev.neighbors[i][j]]
+                    yield self._vertex_to_labels[cg.g_rev.neighbors[i][j]], vi
 
     def iterator_out_edges(self, object vertices, bint labels):
         """
@@ -597,6 +618,7 @@ class StaticSparseBackend(CGraphBackend):
             [(0, 1), (0, 4), (0, 5)]
             sage: list(g.iterator_out_edges([0],True))
             [(0, 1, None), (0, 4, None), (0, 5, None)]
+
         """
         try:
             vertices = [self._vertex_to_int[x] for x in vertices]
@@ -775,15 +797,21 @@ class StaticSparseBackend(CGraphBackend):
             (3, 4), (3, 8), (4, 9), (5, 7), (5, 8), (6, 8), (6, 9), (7, 9)]
         """
         cdef FrozenBitset fb
+        cdef list vertices_int
 
-        if self._directed:
+        if self.directed:
             raise RuntimeError("This is not meant for directed graphs.")
 
         try:
-            vertices = FrozenBitset([self._vertex_to_int[x] for x in vertices])
+            vertices_int = [self._vertex_to_int[x] for x in vertices]
         except KeyError:
             raise LookupError("One of the vertices does not belong to the graph")
 
+        if not vertices_int:
+            return
+
+        vertices = FrozenBitset(vertices_int)
+
         cdef StaticSparseCGraph cg = self._cg
         cdef int i,j,tmp
 

src/sage/graphs/linearextensions.py

@@ -79,8 +79,7 @@ def __init__(self, dag):
         ################
         #Precomputation#
         ################
-        from copy import copy
-        dag_copy = copy(dag)
+        dag_copy = dag.copy(immutable=False)
         le = []
         a  = []
         b  = []