"""
Fast compiled graphs
This is a Cython implementation of the base class for sparse and dense graphs
in Sage. It is not intended for use on its own. Specific graph types should
extend this base class and implement missing functionalities. Whenever
possible, specific methods should also be overridden with implementations that
suit the graph type under consideration.
Data structure
--------------
The class ``CGraph`` maintains the following variables:
- ``cdef int num_verts``
- ``cdef int num_arcs``
- ``cdef int *in_degrees``
- ``cdef int *out_degrees``
- ``cdef bitset_t active_vertices``
The bitset ``active_vertices`` is a list of all available vertices for use, but
only the ones which are set are considered to actually be in the graph. The
variables ``num_verts`` and ``num_arcs`` are self-explanatory. Note that
``num_verts`` is the number of bits set in ``active_vertices``, not the full
length of the bitset. The arrays ``in_degrees`` and ``out_degrees`` are of the
same length as the bitset.
For more information about active vertices, see the documentation for the
method :meth:`realloc <sage.graphs.base.c_graph.CGraph.realloc>`.
"""
include "sage/misc/bitset.pxi"
from graph_backends import GenericGraphBackend
from sage.rings.integer cimport Integer
cdef class CGraph:
"""
Compiled sparse and dense graphs.
"""
cpdef bint has_vertex(self, int n):
"""
Determine whether the vertex ``n`` is in ``self``.
This method is different from :meth:`check_vertex`. The current method
returns a boolean to signify whether or not ``n`` is a vertex of this
graph. On the other hand, :meth:`check_vertex` raises an error if
``n`` is not a vertex of this graph.
INPUT:
- ``n`` -- a nonnegative integer representing a vertex.
OUTPUT:
- ``True`` if ``n`` is a vertex of this graph; ``False`` otherwise.
.. SEEALSO::
- :meth:`check_vertex`
-- raise an error if this graph does not contain a specific
vertex.
EXAMPLES:
Upon initialization, a
:class:`SparseGraph <sage.graphs.base.sparse_graph.SparseGraph>`
or
:class:`DenseGraph <sage.graphs.base.dense_graph.DenseGraph>`
has the first ``nverts`` vertices::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=10, expected_degree=3, extra_vertices=10)
sage: S.has_vertex(6)
True
sage: S.has_vertex(12)
False
sage: S.has_vertex(24)
False
sage: S.has_vertex(-19)
False
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: D = DenseGraph(nverts=10, extra_vertices=10)
sage: D.has_vertex(6)
True
sage: D.has_vertex(12)
False
sage: D.has_vertex(24)
False
sage: D.has_vertex(-19)
False
"""
return (n >= 0 and
n < self.active_vertices.size and
bitset_in(self.active_vertices, n))
cpdef check_vertex(self, int n):
"""
Checks that ``n`` is a vertex of ``self``.
This method is different from :meth:`has_vertex`. The current method
raises an error if ``n`` is not a vertex of this graph. On the other
hand, :meth:`has_vertex` returns a boolean to signify whether or not
``n`` is a vertex of this graph.
INPUT:
- ``n`` -- a nonnegative integer representing a vertex.
OUTPUT:
- Raise an error if ``n`` is not a vertex of this graph.
.. SEEALSO::
- :meth:`has_vertex`
-- determine whether this graph has a specific vertex.
EXAMPLES::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=10, expected_degree=3, extra_vertices=10)
sage: S.check_vertex(4)
sage: S.check_vertex(12)
Traceback (most recent call last):
...
LookupError: Vertex (12) is not a vertex of the graph.
sage: S.check_vertex(24)
Traceback (most recent call last):
...
LookupError: Vertex (24) is not a vertex of the graph.
sage: S.check_vertex(-19)
Traceback (most recent call last):
...
LookupError: Vertex (-19) is not a vertex of the graph.
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: D = DenseGraph(nverts=10, extra_vertices=10)
sage: D.check_vertex(4)
sage: D.check_vertex(12)
Traceback (most recent call last):
...
LookupError: Vertex (12) is not a vertex of the graph.
sage: D.check_vertex(24)
Traceback (most recent call last):
...
LookupError: Vertex (24) is not a vertex of the graph.
sage: D.check_vertex(-19)
Traceback (most recent call last):
...
LookupError: Vertex (-19) is not a vertex of the graph.
"""
if not self.has_vertex(n):
raise LookupError("Vertex ({0}) is not a vertex of the graph.".format(n))
cdef int add_vertex_unsafe(self, int k):
"""
Adds the vertex ``k`` to the graph.
INPUT:
- ``k`` -- nonnegative integer or ``-1``. For `k >= 0`, add the
vertex ``k`` to this graph if the vertex is not already in the graph.
If `k = -1`, this function will find the first available vertex
that is not in ``self`` and add that vertex to this graph.
OUTPUT:
- ``-1`` -- indicates that no vertex was added because the current
allocation is already full or the vertex is out of range.
- nonnegative integer -- this vertex is now guaranteed to be in the
graph.
.. WARNING::
This method is potentially unsafe. You should instead use
:meth:`add_vertex`.
"""
if k == -1:
k = bitset_first_in_complement(self.active_vertices)
elif self.active_vertices.size <= k:
k = -1
if k != -1:
if not bitset_in(self.active_vertices, k):
self.num_verts += 1
bitset_add(self.active_vertices, k)
return k
def add_vertex(self, int k=-1):
"""
Adds vertex ``k`` to the graph.
INPUT:
- ``k`` -- nonnegative integer or ``-1`` (default: ``-1``). If
`k = -1`, a new vertex is added and the integer used is returned.
That is, for `k = -1`, this function will find the first available
vertex that is not in ``self`` and add that vertex to this graph.
OUTPUT:
- ``-1`` -- indicates that no vertex was added because the current
allocation is already full or the vertex is out of range.
- nonnegative integer -- this vertex is now guaranteed to be in the
graph.
.. SEEALSO::
- ``add_vertex_unsafe`` -- add a vertex to a graph. This
method is potentially unsafe. You should instead use
:meth:`add_vertex`.
- ``add_vertices`` -- add a bunch of vertices to a graph.
EXAMPLES:
Adding vertices to a sparse graph::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: G = SparseGraph(3, extra_vertices=3)
sage: G.add_vertex(3)
3
sage: G.add_arc(2, 5)
Traceback (most recent call last):
...
LookupError: Vertex (5) is not a vertex of the graph.
sage: G.add_arc(1, 3)
sage: G.has_arc(1, 3)
True
sage: G.has_arc(2, 3)
False
Adding vertices to a dense graph::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(3, extra_vertices=3)
sage: G.add_vertex(3)
3
sage: G.add_arc(2,5)
Traceback (most recent call last):
...
LookupError: Vertex (5) is not a vertex of the graph.
sage: G.add_arc(1, 3)
sage: G.has_arc(1, 3)
True
sage: G.has_arc(2, 3)
False
Repeatedly adding a vertex using `k = -1` will allocate more memory
as required::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: G = SparseGraph(3, extra_vertices=0)
sage: G.verts()
[0, 1, 2]
sage: for i in range(10):
... _ = G.add_vertex(-1);
...
sage: G.verts()
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(3, extra_vertices=0)
sage: G.verts()
[0, 1, 2]
sage: for i in range(12):
... _ = G.add_vertex(-1);
...
sage: G.verts()
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
TESTS::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: G = SparseGraph(3, extra_vertices=0)
sage: G.add_vertex(6)
Traceback (most recent call last):
...
RuntimeError: Requested vertex is past twice the allocated range: use realloc.
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(3, extra_vertices=0)
sage: G.add_vertex(6)
Traceback (most recent call last):
...
RuntimeError: Requested vertex is past twice the allocated range: use realloc.
"""
if k >= (2 * self.active_vertices.size):
raise RuntimeError(
"Requested vertex is past twice the allocated range: "
"use realloc.")
if (k >= self.active_vertices.size or
(k == -1 and self.active_vertices.size == self.num_verts)):
self.realloc(2 * self.active_vertices.size)
return self.add_vertex_unsafe(k)
cpdef add_vertices(self, object verts):
"""
Adds vertices from the iterable ``verts``.
INPUT:
- ``verts`` -- an iterable of vertices. Value -1 has a special
meaning -- for each such value an unused vertex name is found,
used to create a new vertex and returned.
OUTPUT:
List of generated labels if there is any -1 in ``verts``.
None otherwise.
.. SEEALSO::
- :meth:`add_vertex`
-- add a vertex to a graph.
EXAMPLE:
Adding vertices for sparse graphs::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=4, extra_vertices=4)
sage: S.verts()
[0, 1, 2, 3]
sage: S.add_vertices([3,-1,4,9])
[5]
sage: S.verts()
[0, 1, 2, 3, 4, 5, 9]
sage: S.realloc(20)
sage: S.verts()
[0, 1, 2, 3, 4, 5, 9]
Adding vertices for dense graphs::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: D = DenseGraph(nverts=4, extra_vertices=4)
sage: D.verts()
[0, 1, 2, 3]
sage: D.add_vertices([3,-1,4,9])
[5]
sage: D.verts()
[0, 1, 2, 3, 4, 5, 9]
sage: D.realloc(20)
sage: D.verts()
[0, 1, 2, 3, 4, 5, 9]
"""
cdef int v
cdef int nones = 0
for v in verts:
if v > -1:
self.add_vertex(v)
else:
nones += 1
new_names = []
while nones > 0:
new_names.append(self.add_vertex())
nones -= 1
return new_names if new_names != [] else None
cdef int del_vertex_unsafe(self, int v):
"""
Deletes the vertex ``v``, along with all edges incident to it.
INPUT:
- ``v`` -- nonnegative integer representing a vertex.
OUTPUT:
- None.
.. WARNING::
This method is potentially unsafe. Use :meth:`del_vertex` instead.
"""
cdef int size = 0
cdef int num_nbrs
cdef int i
cdef int *neighbors
if self.in_degrees[v] > size:
size = self.in_degrees[v]
if self.out_degrees[v] > size:
size = self.out_degrees[v]
if size > 0:
neighbors = <int *> sage_malloc(size * sizeof(int))
if not neighbors:
raise RuntimeError("Failure allocating memory.")
num_nbrs = self.in_neighbors_unsafe(v, neighbors, size)
for i from 0 <= i < num_nbrs:
self.del_arc_unsafe(neighbors[i], v)
num_nbrs = self.out_neighbors_unsafe(v, neighbors, size)
for i from 0 <= i < num_nbrs:
self.del_arc_unsafe(v, neighbors[i])
sage_free(neighbors)
self.num_verts -= 1
bitset_remove(self.active_vertices, v)
cpdef del_vertex(self, int v):
"""
Deletes the vertex ``v``, along with all edges incident to it. If ``v``
is not in ``self``, fails silently.
INPUT:
- ``v`` -- a nonnegative integer representing a vertex.
OUTPUT:
- None.
.. SEEALSO::
- ``del_vertex_unsafe`` -- delete a vertex from a graph. This method
is potentially unsafe. Use :meth:`del_vertex` instead.
EXAMPLES:
Deleting vertices of sparse graphs::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: G = SparseGraph(3)
sage: G.add_arc(0, 1)
sage: G.add_arc(0, 2)
sage: G.add_arc(1, 2)
sage: G.add_arc(2, 0)
sage: G.del_vertex(2)
sage: for i in range(2):
... for j in range(2):
... if G.has_arc(i, j):
... print i, j
0 1
sage: G = SparseGraph(3)
sage: G.add_arc(0, 1)
sage: G.add_arc(0, 2)
sage: G.add_arc(1, 2)
sage: G.add_arc(2, 0)
sage: G.del_vertex(1)
sage: for i in xrange(3):
... for j in xrange(3):
... if G.has_arc(i, j):
... print i, j
0 2
2 0
Deleting vertices of dense graphs::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(4)
sage: G.add_arc(0, 1); G.add_arc(0, 2)
sage: G.add_arc(3, 1); G.add_arc(3, 2)
sage: G.add_arc(1, 2)
sage: G.verts()
[0, 1, 2, 3]
sage: G.del_vertex(3); G.verts()
[0, 1, 2]
sage: for i in range(3):
... for j in range(3):
... if G.has_arc(i, j):
... print i, j
...
0 1
0 2
1 2
If the vertex to be deleted is not in this graph, then fail silently::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: G = SparseGraph(3)
sage: G.verts()
[0, 1, 2]
sage: G.has_vertex(3)
False
sage: G.del_vertex(3)
sage: G.verts()
[0, 1, 2]
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(5)
sage: G.verts()
[0, 1, 2, 3, 4]
sage: G.has_vertex(6)
False
sage: G.del_vertex(6)
sage: G.verts()
[0, 1, 2, 3, 4]
"""
if self.has_vertex(v):
self.del_vertex_unsafe(v)
cpdef int current_allocation(self):
"""
Report the number of vertices allocated.
INPUT:
- None.
OUTPUT:
- The number of vertices allocated. This number is usually different
from the order of a graph. We may have allocated enough memory for
a graph to hold `n > 0` vertices, but the order (actual number of
vertices) of the graph could be less than `n`.
EXAMPLES::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=4, extra_vertices=4)
sage: S.current_allocation()
8
sage: S.add_vertex(6)
6
sage: S.current_allocation()
8
sage: S.add_vertex(10)
10
sage: S.current_allocation()
16
sage: S.add_vertex(40)
Traceback (most recent call last):
...
RuntimeError: Requested vertex is past twice the allocated range: use realloc.
sage: S.realloc(50)
sage: S.add_vertex(40)
40
sage: S.current_allocation()
50
sage: S.realloc(30)
-1
sage: S.current_allocation()
50
sage: S.del_vertex(40)
sage: S.realloc(30)
sage: S.current_allocation()
30
The actual number of vertices in a graph might be less than the
number of vertices allocated for the graph::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(nverts=3, extra_vertices=2)
sage: order = len(G.verts())
sage: order
3
sage: G.current_allocation()
5
sage: order < G.current_allocation()
True
"""
return self.active_vertices.size
cpdef list verts(self):
"""
Returns a list of the vertices in ``self``.
INPUT:
- None.
OUTPUT:
- A list of all vertices in this graph.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=4, extra_vertices=4)
sage: S.verts()
[0, 1, 2, 3]
sage: S.add_vertices([3,5,7,9])
sage: S.verts()
[0, 1, 2, 3, 5, 7, 9]
sage: S.realloc(20)
sage: S.verts()
[0, 1, 2, 3, 5, 7, 9]
::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: G = DenseGraph(3, extra_vertices=2)
sage: G.verts()
[0, 1, 2]
sage: G.del_vertex(0)
sage: G.verts()
[1, 2]
"""
cdef int i
return [i for i from 0 <= i < self.active_vertices.size
if bitset_in(self.active_vertices, i)]
cpdef realloc(self, int total):
"""
Reallocate the number of vertices to use, without actually adding any.
INPUT:
- ``total`` -- integer; the total size to make the array of vertices.
OUTPUT:
- Raise a ``NotImplementedError``. This method is not implemented in
this base class. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`realloc <sage.graphs.base.sparse_graph.SparseGraph.realloc>`
-- a ``realloc`` implementation for sparse graphs.
- :meth:`realloc <sage.graphs.base.dense_graph.DenseGraph.realloc>`
-- a ``realloc`` implementation for dense graphs.
EXAMPLES:
First, note that :meth:`realloc` is implemented for
:class:`SparseGraph <sage.graphs.base.sparse_graph.SparseGraph>`
and
:class:`DenseGraph <sage.graphs.base.dense_graph.DenseGraph>`
differently, and is not implemented at the
:class:`CGraph` level::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.realloc(20)
Traceback (most recent call last):
...
NotImplementedError
The ``realloc`` implementation for sparse graphs::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: S = SparseGraph(nverts=4, extra_vertices=4)
sage: S.current_allocation()
8
sage: S.add_vertex(6)
6
sage: S.current_allocation()
8
sage: S.add_vertex(10)
10
sage: S.current_allocation()
16
sage: S.add_vertex(40)
Traceback (most recent call last):
...
RuntimeError: Requested vertex is past twice the allocated range: use realloc.
sage: S.realloc(50)
sage: S.add_vertex(40)
40
sage: S.current_allocation()
50
sage: S.realloc(30)
-1
sage: S.current_allocation()
50
sage: S.del_vertex(40)
sage: S.realloc(30)
sage: S.current_allocation()
30
The ``realloc`` implementation for dense graphs::
sage: from sage.graphs.base.dense_graph import DenseGraph
sage: D = DenseGraph(nverts=4, extra_vertices=4)
sage: D.current_allocation()
8
sage: D.add_vertex(6)
6
sage: D.current_allocation()
8
sage: D.add_vertex(10)
10
sage: D.current_allocation()
16
sage: D.add_vertex(40)
Traceback (most recent call last):
...
RuntimeError: Requested vertex is past twice the allocated range: use realloc.
sage: D.realloc(50)
sage: D.add_vertex(40)
40
sage: D.current_allocation()
50
sage: D.realloc(30)
-1
sage: D.current_allocation()
50
sage: D.del_vertex(40)
sage: D.realloc(30)
sage: D.current_allocation()
30
"""
raise NotImplementedError()
cdef int add_arc_unsafe(self, int u, int v) except? -1:
raise NotImplementedError()
cdef int has_arc_unsafe(self, int u, int v) except? -1:
raise NotImplementedError()
cdef int del_arc_unsafe(self, int u, int v) except? -1:
raise NotImplementedError()
cdef int out_neighbors_unsafe(self, int u, int *neighbors, int size) except? -2:
raise NotImplementedError()
cdef int in_neighbors_unsafe(self, int u, int *neighbors, int size) except? -2:
raise NotImplementedError()
cpdef add_arc(self, int u, int v):
"""
Add the given arc to this graph.
INPUT:
- ``u`` -- integer; the tail of an arc.
- ``v`` -- integer; the head of an arc.
OUTPUT:
- Raise ``NotImplementedError``. This method is not implemented at
the :class:`CGraph` level. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`add_arc <sage.graphs.base.sparse_graph.SparseGraph.add_arc>`
-- ``add_arc`` method for sparse graphs.
- :meth:`add_arc <sage.graphs.base.dense_graph.DenseGraph.add_arc>`
-- ``add_arc`` method for dense graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.add_arc(0, 1)
Traceback (most recent call last):
...
NotImplementedError
"""
raise NotImplementedError()
cpdef bint has_arc(self, int u, int v) except -1:
"""
Determine whether or not the given arc is in this graph.
INPUT:
- ``u`` -- integer; the tail of an arc.
- ``v`` -- integer; the head of an arc.
OUTPUT:
- Print a ``Not Implemented!`` message. This method is not implemented
at the :class:`CGraph` level. A child class should provide a
suitable implementation.
.. SEEALSO::
- :meth:`has_arc <sage.graphs.base.sparse_graph.SparseGraph.has_arc>`
-- ``has_arc`` method for sparse graphs.
- :meth:`has_arc <sage.graphs.base.dense_graph.DenseGraph.has_arc>`
-- ``has_arc`` method for dense graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.has_arc(0, 1)
Not Implemented!
False
"""
print "Not Implemented!"
cpdef del_all_arcs(self, int u, int v):
"""
Delete all arcs from ``u`` to ``v``.
INPUT:
- ``u`` -- integer; the tail of an arc.
- ``v`` -- integer; the head of an arc.
OUTPUT:
- Raise ``NotImplementedError``. This method is not implemented at the
:class:`CGraph` level. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`del_all_arcs <sage.graphs.base.sparse_graph.SparseGraph.del_all_arcs>`
-- ``del_all_arcs`` method for sparse graphs.
- :meth:`del_all_arcs <sage.graphs.base.dense_graph.DenseGraph.del_all_arcs>`
-- ``del_all_arcs`` method for dense graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.del_all_arcs(0,1)
Traceback (most recent call last):
...
NotImplementedError
"""
raise NotImplementedError()
cdef adjacency_sequence_in(self, int n, int *vertices, int v, int* sequence):
r"""
Computes the adjacency sequence corresponding to a list of vertices
and a vertex.
This method fills the array ``sequence``, whose i-th element is set to
`1` iff ``(v,vertices[i])`` is an edge.
See the function ``_test_adjacency_sequence()`` of
``dense_graph.pyx`` and ``sparse_graph.pyx`` for unit tests.
INPUT:
- ``n`` -- nonnegative integer; the maximum index in
``vertices`` up to which we want to consider. If ``n = 0``,
we only want to know if ``(vertices[0],v)`` is an edge. If
``n = 1``, we want to know whether ``(vertices[0],v)`` and
``(vertices[1],v)`` are edges. Let ``k`` be the length of
``vertices``. If ``0 <= n < k``, then we want to know if
``v`` is adjacent to each of ``vertices[0], vertices[1],
..., vertices[n]``. Where ``n = k - 1``, then we consider
all elements in the list ``vertices``.
- ``vertices`` -- list of vertices.
- ``v`` -- a vertex.
- ``sequence`` (int *) -- the memory segment of length `>= n` that is to
be filled.
.. SEEALSO::
- :meth:`adjacency_sequence_out` -- Similar method for
``(v, vertices[i])`` instead of ``(vertices[i], v)`` (the
difference only matters for digraphs).
"""
cdef int i = 0
for 0 <= i < n:
sequence[i] = self.has_arc_unsafe(vertices[i], v)
cdef adjacency_sequence_out(self, int n, int *vertices, int v, int* sequence):
r"""
Returns the adjacency sequence corresponding to a list of vertices
and a vertex.
This method fills the array ``sequence``, whose i-th element is set to
`1` iff ``(v,vertices[i])`` is an edge.
See the function ``_test_adjacency_sequence()`` of
``dense_graph.pyx`` and ``sparse_graph.pyx`` for unit tests.
INPUT:
- ``n`` -- nonnegative integer; the maximum index in
``vertices`` up to which we want to consider. If ``n = 0``,
we only want to know if ``(v, vertices[0])`` is an edge. If
``n = 1``, we want to know whether ``(v, vertices[0])`` and
``(v, vertices[1])`` are edges. Let ``k`` be the length of
``vertices``. If ``0 <= n < k``, then we want to know if
each of ``vertices[0], vertices[1], ..., vertices[n]`` is
adjacent to ``v``. Where ``n = k - 1``, then we consider all
elements in the list ``vertices``.
- ``vertices`` -- list of vertices.
- ``v`` -- a vertex.
- ``sequence`` (int *) -- the memory segment of length `>= n` that is to
be filled.
.. SEEALSO::
- :meth:`adjacency_sequence_in` -- Similar method for
``(vertices[i],v)`` instead of ``(v,vertices[i])`` (the
difference only matters for digraphs).
"""
cdef int i = 0
for 0 <= i < n:
sequence[i] = self.has_arc_unsafe(v, vertices[i])
cpdef list all_arcs(self, int u, int v):
"""
Return the labels of all arcs from ``u`` to ``v``.
INPUT:
- ``u`` -- integer; the tail of an arc.
- ``v`` -- integer; the head of an arc.
OUTPUT:
- Raise ``NotImplementedError``. This method is not implemented at the
:class:`CGraph` level. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`all_arcs <sage.graphs.base.sparse_graph.SparseGraph.all_arcs>`
-- ``all_arcs`` method for sparse graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.all_arcs(0, 1)
Traceback (most recent call last):
...
NotImplementedError
"""
raise NotImplementedError()
cpdef list in_neighbors(self, int v):
"""
Gives the in-neighbors of the vertex ``v``.
INPUT:
- ``v`` -- integer representing a vertex of this graph.
OUTPUT:
- Raise ``NotImplementedError``. This method is not implemented at
the :class:`CGraph` level. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`in_neighbors <sage.graphs.base.sparse_graph.SparseGraph.in_neighbors>`
-- ``in_neighbors`` method for sparse graphs.
- :meth:`in_neighbors <sage.graphs.base.dense_graph.DenseGraph.in_neighbors>`
-- ``in_neighbors`` method for dense graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.in_neighbors(0)
Traceback (most recent call last):
...
NotImplementedError
"""
raise NotImplementedError()
cpdef list out_neighbors(self, int u):
"""
Gives the out-neighbors of the vertex ``u``.
INPUT:
- ``u`` -- integer representing a vertex of this graph.
OUTPUT:
- Raise ``NotImplementedError``. This method is not implemented at the
:class:`CGraph` level. A child class should provide a suitable
implementation.
.. SEEALSO::
- :meth:`out_neighbors <sage.graphs.base.sparse_graph.SparseGraph.out_neighbors>`
-- ``out_neighbors`` implementation for sparse graphs.
- :meth:`out_neighbors <sage.graphs.base.dense_graph.DenseGraph.out_neighbors>`
-- ``out_neighbors`` implementation for dense graphs.
EXAMPLE::
sage: from sage.graphs.base.c_graph import CGraph
sage: G = CGraph()
sage: G.out_neighbors(0)
Traceback (most recent call last):
...
NotImplementedError
"""
raise NotImplementedError()
def _in_degree(self, int v):
"""
Return the number of edges coming into ``v``.
INPUT:
- ``v`` -- a vertex of this graph.
OUTPUT:
- The number of in-neighbors of ``v``.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: SparseGraph(7)._in_degree(3)
0
TEST::
sage: g = Graph({1: [2,5], 2: [1,5,3,4], 3: [2,5], 4: [3], 5: [2,3]}, implementation="c_graph")
sage: g._backend.degree(5, False)
3
"""
if not self.has_vertex(v):
raise LookupError("Vertex ({0}) is not a vertex of the graph.".format(v))
return self.in_degrees[v]
def _out_degree(self, int v):
"""
Return the number of edges coming out of ``v``.
INPUT:
- ``v`` -- a vertex of this graph.
OUTPUT:
- The number of out-neighbors of ``v``.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: SparseGraph(7)._out_degree(3)
0
"""
if not self.has_vertex(v):
raise LookupError("Vertex ({0}) is not a vertex of the graph.".format(v))
return self.out_degrees[v]
def _num_verts(self):
"""
Return the number of vertices in the (di)graph.
INPUT:
- None.
OUTPUT:
- The order of this graph.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: SparseGraph(7)._num_verts()
7
"""
return self.num_verts
def _num_arcs(self):
"""
Return the number of arcs in ``self``.
INPUT:
- None.
OUTPUT:
- The size of this graph.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraph
sage: SparseGraph(7)._num_arcs()
0
"""
return self.num_arcs
cdef int get_vertex(object u, dict vertex_ints, dict vertex_labels,
CGraph G) except ? -2:
"""
Returns an int representing the arbitrary hashable vertex u (whether or not
u is actually in the graph), or -1 if a new association must be made for u
to be a vertex.
TESTS:
We check that the bug described in :trac:`8406` is gone::
sage: G = Graph()
sage: R.<a> = GF(3**3)
sage: S.<x> = R[]
sage: G.add_vertex(a**2)
sage: G.add_vertex(x)
sage: G.vertices()
[a^2, x]
And that the bug described in :trac:`9610` is gone::
sage: n = 20
sage: k = 3
sage: g = DiGraph()
sage: g.add_edges( (i,Mod(i+j,n)) for i in range(n) for j in range(1,k+1) )
sage: g.vertices()
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
sage: g.strongly_connected_components()
[[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]]
The bug in :trac:`14967` and :trac:`14853` is fixed::
sage: DiGraph({0: {}, 1/2: {}})
Multi-digraph on 2 vertices
sage: A = Set([RDF.random_element(min=0, max=10) for k in range(10)])
sage: G = Graph()
sage: G.add_vertices(A)
sage: Set(G.vertices()) == A
True
"""
cdef int u_int
if u in vertex_ints:
return vertex_ints[u]
try:
u_int = u
except Exception:
return -1
if u_int < 0 or u_int >= G.active_vertices.size or u_int in vertex_labels or u_int != u:
return -1
return u_int
cdef object vertex_label(int u_int, dict vertex_ints, dict vertex_labels,
CGraph G):
"""
Returns the object represented by u_int, or None if this does not represent
a vertex.
"""
if u_int in vertex_labels:
return vertex_labels[u_int]
elif bitset_in(G.active_vertices, u_int):
return u_int
else:
return None
cdef int check_vertex(object u, dict vertex_ints, dict vertex_labels,
CGraph G, CGraph G_rev, bint reverse) except ? -1:
"""
Returns an int representing the arbitrary hashable vertex u, and updates,
if necessary, the translation dict and list. Adds a vertex if the label
is new.
"""
cdef int u_int = get_vertex(u, vertex_ints, vertex_labels, G)
if u_int != -1:
if not bitset_in(G.active_vertices, u_int):
bitset_add(G.active_vertices, u_int)
G.num_verts += 1
if reverse:
bitset_add(G_rev.active_vertices, u_int)
G_rev.num_verts += 1
return u_int
u_int = bitset_first_in_complement(G.active_vertices)
if u_int == -1:
G.realloc(2*G.active_vertices.size)
if reverse:
G_rev.realloc(2*G_rev.active_vertices.size)
return check_vertex(u, vertex_ints, vertex_labels, G, G_rev, reverse)
vertex_labels[u_int] = u
vertex_ints[u] = u_int
G.add_vertex(u_int)
if reverse:
G_rev.add_vertex(u_int)
return u_int
class CGraphBackend(GenericGraphBackend):
"""
Base class for sparse and dense graph backends.
::
sage: from sage.graphs.base.c_graph import CGraphBackend
This class is extended by
:class:`SparseGraphBackend <sage.graphs.base.sparse_graph.SparseGraphBackend>`
and
:class:`DenseGraphBackend <sage.graphs.base.dense_graph.DenseGraphBackend>`,
which are fully functional backends. This class is mainly just for vertex
functions, which are the same for both. A :class:`CGraphBackend` will not
work on its own::
sage: from sage.graphs.base.c_graph import CGraphBackend
sage: CGB = CGraphBackend()
sage: CGB.degree(0, True)
Traceback (most recent call last):
...
AttributeError: 'CGraphBackend' object has no attribute 'vertex_ints'
The appropriate way to use these backends is via Sage graphs::
sage: G = Graph(30, implementation="c_graph")
sage: G.add_edges([(0,1), (0,3), (4,5), (9, 23)])
sage: G.edges(labels=False)
[(0, 1), (0, 3), (4, 5), (9, 23)]
.. SEEALSO::
- :class:`SparseGraphBackend <sage.graphs.base.sparse_graph.SparseGraphBackend>`
-- backend for sparse graphs.
- :class:`DenseGraphBackend <sage.graphs.base.dense_graph.DenseGraphBackend>`
-- backend for dense graphs.
"""
_cg = None
_cg_rev = None
_directed = None
def has_vertex(self, v):
"""
Returns whether ``v`` is a vertex of ``self``.
INPUT:
- ``v`` -- any object.
OUTPUT:
- ``True`` if ``v`` is a vertex of this graph; ``False`` otherwise.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraphBackend
sage: B = SparseGraphBackend(7)
sage: B.has_vertex(6)
True
sage: B.has_vertex(7)
False
"""
cdef v_int = get_vertex(v, self.vertex_ints, self.vertex_labels,
self._cg)
if v_int == -1:
return False
if not bitset_in((<CGraph>self._cg).active_vertices, v_int):
return False
return True
def degree(self, v, directed):
"""
Return the degree of the vertex ``v``.
INPUT:
- ``v`` -- a vertex of the graph.
- ``directed`` -- boolean; whether to take into account the
orientation of this graph in counting the degree of ``v``.
OUTPUT:
- The degree of vertex ``v``.
EXAMPLE::
sage: from sage.graphs.base.sparse_graph import SparseGraphBackend
sage: B = SparseGraphBackend(7)
sage: B.degree(3, False)
0
TESTS:
Ensure that ticket :trac:`8395` is fixed. ::
sage: def my_add_edges(G, m, n):
... for i in range(m):
... u = randint(0, n)
... v = randint(0, n)
... G.add_edge(u, v)
sage: G = Graph({1:[1]}); G
Looped graph on 1 vertex
sage: G.edges(labels=False)
[(1, 1)]
sage: G.degree(); G.size()
[2]
1
sage: sum(G.degree()) == 2 * G.size()
True
sage: G = Graph({1:[1,2], 2:[2,3]}, loops=True); G
Looped graph on 3 vertices
sage: my_add_edges(G, 100, 50)
sage: sum(G.degree()) == 2 * G.size()
True
sage: G = Graph({1:[2,2], 2:[3]}); G
Multi-graph on 3 vertices
sage: G.edges(labels=False)
[(1, 2), (1, 2), (2, 3)]
sage: G.degree(); G.size()
[2, 3, 1]
3
sage: sum(G.degree()) == 2 * G.size()
True
sage: G.allow_loops(True); G
Looped multi-graph on 3 vertices
sage: my_add_edges(G, 100, 50)
sage: sum(G.degree()) == 2 * G.size()
True
sage: D = DiGraph({1:[2], 2:[1,3]}); D
Digraph on 3 vertices
sage: D.edges(labels=False)
[(1, 2), (2, 1), (2, 3)]
sage: D.degree(); D.size()
[2, 3, 1]
3
sage: sum(D.degree()) == 2 * D.size()
True
sage: D.allow_loops(True); D
Looped digraph on 3 vertices
sage: my_add_edges(D, 100, 50)
sage: sum(D.degree()) == 2 * D.size()
True
sage: D.allow_multiple_edges(True)
sage: my_add_edges(D, 200, 50)
sage: sum(D.degree()) == 2 * D.size()
True
sage: G = Graph({1:[2,2,2]})
sage: G.allow_loops(True)
sage: G.add_edge(1,1)
sage: G.add_edge(1,1)
sage: G.edges(labels=False)
[(1, 1), (1, 1), (1, 2), (1, 2), (1, 2)]
sage: G.degree(1)
7
sage: G.allow_loops(False)
sage: G.edges(labels=False)
[(1, 2), (1, 2), (1, 2)]
sage: G.degree(1)
3
sage: G = Graph({1:{2:['a','a','a']}})
sage: G.allow_loops(True)
sage: G.add_edge(1,1,'b')
sage: G.add_edge(1,1,'b')
sage: G.add_edge(1,1)
sage: G.add_edge(1,1)
sage: G.edges()
[(1, 1, None), (1, 1, None), (1, 1, 'b'), (1, 1, 'b'), (1, 2, 'a'), (1, 2, 'a'), (1, 2, 'a')]
sage: G.degree(1)
11
sage: G.allow_loops(False)
sage: G.edges()
[(1, 2, 'a'), (1, 2, 'a'), (1, 2, 'a')]
sage: G.degree(1)
3
sage: G = Graph({1:{2:['a','a','a']}})
sage: G.allow_loops(True)
sage: G.add_edge(1,1,'b')
sage: G.add_edge(1,1,'b')
sage: G.edges()
[(1, 1, 'b'), (1, 1, 'b'), (1, 2, 'a'), (1, 2, 'a'), (1, 2, 'a')]
sage: G.degree(1)
7
sage: G.allow_loops(False)
sage: G.edges()
[(1, 2, 'a'), (1, 2, 'a'), (1, 2, 'a')]
sage: G.degree(1)
3
Ensure that :trac:`13664` is fixed ::
sage: W = WeylGroup(["A",1])
sage: G = W.cayley_graph()
sage: Graph(G).degree()
[1, 1]
sage: h = Graph()
sage: h.add_edge(1,2,"a")
sage: h.add_edge(1,2,"a")
sage: h.degree()
[1, 1]
"""
cdef v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
if directed:
return self._cg._in_degree(v_int) + self._cg._out_degree(v_int)
d = 0
if self._loops and self.has_edge(v, v, None):
if self._multiple_edges:
d += len(self.get_edge_label(v, v))
else:
d += 1
return self._cg._out_degree(v_int) + d
def out_degree(self, v):
r"""
Returns the out-degree of v
INPUT:
- ``v`` -- a vertex of the graph.
- ``directed`` -- boolean; whether to take into account the
orientation of this graph in counting the degree of ``v``.
EXAMPLE::
sage: D = DiGraph( { 0: [1,2,3], 1: [0,2], 2: [3], 3: [4], 4: [0,5], 5: [1] } )
sage: D.out_degree(1)
2
"""
cdef v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
if self._directed:
return self._cg._out_degree(v_int)
d = 0
if self._loops and self.has_edge(v, v, None):
if self._multiple_edges:
d += len(self.get_edge_label(v, v))
else:
d += 1
return self._cg._out_degree(v_int) + d
def add_vertex(self, object name):
"""
Add a vertex to ``self``.
INPUT:
- ``name`` -- the vertex to be added (must be hashable). If ``None``,
a new name is created.
OUTPUT:
- If name=None, the new vertex name is returned.
None otherwise.
.. SEEALSO::
- :meth:`add_vertices`
-- add a bunch of vertices of this graph.
- :meth:`has_vertex`
-- returns whether or not this graph has a specific vertex.
EXAMPLE::
sage: D = sage.graphs.base.dense_graph.DenseGraphBackend(9)
sage: D.add_vertex(10)
sage: D.add_vertex([])
Traceback (most recent call last):
...
TypeError: unhashable type: 'list'
::
sage: S = sage.graphs.base.sparse_graph.SparseGraphBackend(9)
sage: S.add_vertex(10)
sage: S.add_vertex([])
Traceback (most recent call last):
...
TypeError: unhashable type: 'list'
"""
retval = None
if name is None:
name = 0
while name in self.vertex_ints or (
name not in self.vertex_labels and
bitset_in((<CGraph>self._cg).active_vertices, name)):
name += 1
retval = name
check_vertex(name,
self.vertex_ints,
self.vertex_labels,
self._cg,
self._cg_rev,
(self._directed and
self._cg_rev is not None))
return retval
def add_vertices(self, object vertices):
"""
Add vertices to ``self``.
INPUT:
- ``vertices``: iterator of vertex labels. A new name is created, used and returned in
the output list for all ``None`` values in ``vertices``.
OUTPUT:
Generated names of new vertices if there is at least one ``None`` value
present in ``vertices``. ``None`` otherwise.
.. SEEALSO::
- :meth:`add_vertex`
-- add a vertex to this graph.
EXAMPLE::
sage: D = sage.graphs.base.sparse_graph.SparseGraphBackend(1)
sage: D.add_vertices([1,2,3])
sage: D.add_vertices([None]*4)
[4, 5, 6, 7]
::
sage: G = sage.graphs.base.sparse_graph.SparseGraphBackend(0)
sage: G.add_vertices([0,1])
sage: list(G.iterator_verts(None))
[0, 1]
sage: list(G.iterator_edges([0,1], True))
[]
::
sage: import sage.graphs.base.dense_graph
sage: D = sage.graphs.base.dense_graph.DenseGraphBackend(9)
sage: D.add_vertices([10,11,12])
"""
cdef object v
cdef int nones = 0
for v in vertices:
if v is not None:
self.add_vertex(v)
else:
nones += 1
new_names = []
while nones > 0:
new_names.append(self.add_vertex(None))
nones -= 1
return new_names if new_names != [] else None
def del_vertex(self, v):
"""
Delete a vertex in ``self``, failing silently if the vertex is not
in the graph.
INPUT:
- ``v`` -- vertex to be deleted.
OUTPUT:
- None.
.. SEEALSO::
- :meth:`del_vertices`
-- delete a bunch of vertices from this graph.
EXAMPLE::
sage: D = sage.graphs.base.dense_graph.DenseGraphBackend(9)
sage: D.del_vertex(0)
sage: D.has_vertex(0)
False
::
sage: S = sage.graphs.base.sparse_graph.SparseGraphBackend(9)
sage: S.del_vertex(0)
sage: S.has_vertex(0)
False
"""
if not self.has_vertex(v):
return
cdef int v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
self._cg.del_vertex(v_int)
if self._cg_rev is not None:
self._cg_rev.del_vertex(v_int)
if v_int in self.vertex_labels:
self.vertex_ints.pop(v)
self.vertex_labels.pop(v_int)
def del_vertices(self, vertices):
"""
Delete vertices from an iterable container.
INPUT:
- ``vertices`` -- iterator of vertex labels.
OUTPUT:
- Same as for :meth:`del_vertex`.
.. SEEALSO::
- :meth:`del_vertex`
-- delete a vertex of this graph.
EXAMPLE::
sage: import sage.graphs.base.dense_graph
sage: D = sage.graphs.base.dense_graph.DenseGraphBackend(9)
sage: D.del_vertices([7,8])
sage: D.has_vertex(7)
False
sage: D.has_vertex(6)
True
::
sage: D = sage.graphs.base.sparse_graph.SparseGraphBackend(9)
sage: D.del_vertices([1,2,3])
sage: D.has_vertex(1)
False
sage: D.has_vertex(0)
True
"""
cdef object v
for v in vertices:
self.del_vertex(v)
def iterator_nbrs(self, v):
"""
Returns an iterator over the neighbors of ``v``.
INPUT:
- ``v`` -- a vertex of this graph.
OUTPUT:
- An iterator over the neighbors the vertex ``v``.
.. SEEALSO::
- :meth:`iterator_in_nbrs`
-- returns an iterator over the in-neighbors of a vertex.
- :meth:`iterator_out_nbrs`
-- returns an iterator over the out-neighbors of a vertex.
- :meth:`iterator_verts`
-- returns an iterator over a given set of vertices.
EXAMPLE::
sage: P = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: list(P._backend.iterator_nbrs(0))
[1, 4, 5]
"""
if not self._directed:
return self.iterator_out_nbrs(v)
return iter(set(self.iterator_in_nbrs(v)) |
set(self.iterator_out_nbrs(v)))
def iterator_in_nbrs(self, v):
"""
Returns an iterator over the incoming neighbors of ``v``.
INPUT:
- ``v`` -- a vertex of this graph.
OUTPUT:
- An iterator over the in-neighbors of the vertex ``v``.
.. SEEALSO::
- :meth:`iterator_nbrs`
-- returns an iterator over the neighbors of a vertex.
- :meth:`iterator_out_nbrs`
-- returns an iterator over the out-neighbors of a vertex.
EXAMPLE::
sage: P = DiGraph(graphs.PetersenGraph().to_directed(), implementation="c_graph")
sage: list(P._backend.iterator_in_nbrs(0))
[1, 4, 5]
"""
cdef int u_int
cdef int v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
if self._cg_rev is not None:
for u_int in self._cg_rev.out_neighbors(v_int):
yield vertex_label(u_int, self.vertex_ints, self.vertex_labels, self._cg)
else:
for u_int in self._cg.in_neighbors(v_int):
yield vertex_label(u_int, self.vertex_ints, self.vertex_labels, self._cg)
def iterator_out_nbrs(self, v):
"""
Returns an iterator over the outgoing neighbors of ``v``.
INPUT:
- ``v`` -- a vertex of this graph.
OUTPUT:
- An iterator over the out-neighbors of the vertex ``v``.
.. SEEALSO::
- :meth:`iterator_nbrs`
-- returns an iterator over the neighbors of a vertex.
- :meth:`iterator_in_nbrs`
-- returns an iterator over the in-neighbors of a vertex.
EXAMPLE::
sage: P = DiGraph(graphs.PetersenGraph().to_directed(), implementation="c_graph")
sage: list(P._backend.iterator_out_nbrs(0))
[1, 4, 5]
"""
cdef u_int
cdef int v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
for u_int in self._cg.out_neighbors(v_int):
yield vertex_label(u_int, self.vertex_ints, self.vertex_labels, self._cg)
def iterator_verts(self, verts=None):
"""
Returns an iterator over the vertices of ``self`` intersected with
``verts``.
INPUT:
- ``verts`` -- an iterable container of objects (default: ``None``).
OUTPUT:
- If ``verts=None``, return an iterator over all vertices of this
graph.
- If ``verts`` is an iterable container of vertices, find the
intersection of ``verts`` with the vertex set of this graph and
return an iterator over the resulting intersection.
.. SEEALSO::
- :meth:`iterator_nbrs`
-- returns an iterator over the neighbors of a vertex.
EXAMPLE::
sage: P = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: list(P._backend.iterator_verts(P))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
sage: list(P._backend.iterator_verts())
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
sage: list(P._backend.iterator_verts([1, 2, 3]))
[1, 2, 3]
sage: list(P._backend.iterator_verts([1, 2, 10]))
[1, 2]
"""
cdef int i
cdef object v
if verts is None:
S = set(self.vertex_ints.iterkeys())
for i from 0 <= i < (<CGraph>self._cg).active_vertices.size:
if (i not in self.vertex_labels and
bitset_in((<CGraph>self._cg).active_vertices, i)):
S.add(i)
return iter(S)
is_hashable = False
try:
v = hash(verts)
is_hashable = True
except Exception:
pass
if is_hashable and self.has_vertex(verts):
return iter([verts])
else:
L = []
for v in verts:
if self.has_vertex(v):
L.append(v)
return iter(L)
def loops(self, new=None):
"""
Returns whether loops are allowed in this graph.
INPUT:
- ``new`` -- (default: ``None``); boolean (to set) or ``None``
(to get).
OUTPUT:
- If ``new=None``, return ``True`` if this graph allows self-loops or
``False`` if self-loops are not allowed.
- If ``new`` is a boolean, set the self-loop permission of this graph
according to the boolean value of ``new``.
EXAMPLE::
sage: G = Graph(implementation='c_graph')
sage: G._backend.loops()
False
sage: G._backend.loops(True)
sage: G._backend.loops()
True
"""
if new is None:
return self._loops
if new:
self._loops = True
else:
self._loops = False
def num_edges(self, directed):
"""
Returns the number of edges in ``self``.
INPUT:
- ``directed`` -- boolean; whether to count ``(u,v)`` and ``(v,u)``
as one or two edges.
OUTPUT:
- If ``directed=True``, counts the number of directed edges in this
graph. Otherwise, return the size of this graph.
.. SEEALSO::
- :meth:`num_verts`
-- return the order of this graph.
EXAMPLE::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: G._backend.num_edges(False)
15
TESTS:
Ensure that ticket #8395 is fixed. ::
sage: G = Graph({1:[1]}); G
Looped graph on 1 vertex
sage: G.edges(labels=False)
[(1, 1)]
sage: G.size()
1
sage: G = Graph({1:[2,2]}); G
Multi-graph on 2 vertices
sage: G.edges(labels=False)
[(1, 2), (1, 2)]
sage: G.size()
2
sage: G = Graph({1:[1,1]}); G
Looped multi-graph on 1 vertex
sage: G.edges(labels=False)
[(1, 1), (1, 1)]
sage: G.size()
2
sage: D = DiGraph({1:[1]}); D
Looped digraph on 1 vertex
sage: D.edges(labels=False)
[(1, 1)]
sage: D.size()
1
sage: D = DiGraph({1:[2,2], 2:[1,1]}); D
Multi-digraph on 2 vertices
sage: D.edges(labels=False)
[(1, 2), (1, 2), (2, 1), (2, 1)]
sage: D.size()
4
sage: D = DiGraph({1:[1,1]}); D
Looped multi-digraph on 1 vertex
sage: D.edges(labels=False)
[(1, 1), (1, 1)]
sage: D.size()
2
sage: from sage.graphs.base.sparse_graph import SparseGraphBackend
sage: S = SparseGraphBackend(7)
sage: S.num_edges(directed=False)
0
sage: S.loops(True)
sage: S.add_edge(1, 1, None, directed=False)
sage: S.num_edges(directed=False)
1
sage: S.multiple_edges(True)
sage: S.add_edge(1, 1, None, directed=False)
sage: S.num_edges(directed=False)
2
sage: from sage.graphs.base.dense_graph import DenseGraphBackend
sage: D = DenseGraphBackend(7)
sage: D.num_edges(directed=False)
0
sage: D.loops(True)
sage: D.add_edge(1, 1, None, directed=False)
sage: D.num_edges(directed=False)
1
"""
if directed:
return self._cg._num_arcs()
else:
i = self._cg._num_arcs()
k = 0
if self.loops(None):
if self.multiple_edges(None):
for j in self.iterator_verts():
if self.has_edge(j, j, None):
k += len(self.get_edge_label(j, j))
else:
for j in self.iterator_verts():
if self.has_edge(j, j, None):
k += 1
i = (i - k) / 2
return i + k
def num_verts(self):
"""
Returns the number of vertices in ``self``.
INPUT:
- None.
OUTPUT:
- The order of this graph.
.. SEEALSO::
- :meth:`num_edges`
-- return the number of (directed) edges in this graph.
EXAMPLE::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: G._backend.num_verts()
10
"""
return (<CGraph>self._cg).num_verts
def relabel(self, perm, directed):
"""
Relabels the graph according to ``perm``.
INPUT:
- ``perm`` -- anything which represents a permutation as
``v --> perm[v]``, for example a dict or a list.
- ``directed`` -- ignored (this is here for compatibility with other
backends).
EXAMPLES::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: G._backend.relabel(range(9,-1,-1), False)
sage: G.edges()
[(0, 2, None),
(0, 3, None),
(0, 5, None),
(1, 3, None),
(1, 4, None),
(1, 6, None),
(2, 4, None),
(2, 7, None),
(3, 8, None),
(4, 9, None),
(5, 6, None),
(5, 9, None),
(6, 7, None),
(7, 8, None),
(8, 9, None)]
"""
cdef int i
cdef object v
cdef dict new_vx_ints = {}
cdef dict new_vx_labels = {}
for v in self.iterator_verts(None):
i = get_vertex(v, self.vertex_ints, self.vertex_labels, self._cg)
new_vx_ints[perm[v]] = i
new_vx_labels[i] = perm[v]
self.vertex_ints = new_vx_ints
self.vertex_labels = new_vx_labels
def shortest_path(self, x, y):
r"""
Returns the shortest path between ``x`` and ``y``.
INPUT:
- ``x`` -- the starting vertex in the shortest path from ``x`` to
``y``.
- ``y`` -- the end vertex in the shortest path from ``x`` to ``y``.
OUTPUT:
- A list of vertices in the shortest path from ``x`` to ``y``.
EXAMPLE::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: G.shortest_path(0, 1)
[0, 1]
"""
if x == y:
return 0
cdef int x_int = get_vertex(x,
self.vertex_ints,
self.vertex_labels,
self._cg)
cdef int y_int = get_vertex(y,
self.vertex_ints,
self.vertex_labels,
self._cg)
cdef int u = 0
cdef int v = 0
cdef int w = 0
cdef dict pred_x = {}
cdef dict pred_y = {}
cdef dict pred_current = pred_x
cdef dict pred_other = pred_y
cdef dict dist_x = {}
cdef dict dist_y = {}
cdef dict dist_current = dist_x
cdef dict dist_other = dist_y
dist_x[x_int] = 0
dist_y[y_int] = 0
cdef list next_x = [x_int]
cdef list next_y = [y_int]
cdef list next_current = next_x
cdef list next_other = next_y
cdef list next_temporary = []
cdef list neighbors
cdef list shortest_path = []
cdef int out = 1
while next_current:
next_temporary = []
for u in next_current:
if out == 1:
neighbors = self._cg.out_neighbors(u)
elif self._cg_rev is not None:
neighbors = self._cg_rev.out_neighbors(u)
else:
neighbors = self._cg.in_neighbors(u)
for v in neighbors:
if v not in dist_current:
dist_current[v] = dist_current[u] + 1
pred_current[v] = u
next_current.append(v)
if v in dist_other:
w = v
while w != x_int:
shortest_path.append(
vertex_label(w,
self.vertex_ints,
self.vertex_labels,
self._cg))
w = pred_x[w]
shortest_path.append(x)
shortest_path.reverse()
if v == y_int:
return shortest_path
w = pred_y[v]
while w != y_int:
shortest_path.append(
vertex_label(w,
self.vertex_ints,
self.vertex_labels,
self._cg))
w = pred_y[w]
shortest_path.append(y)
return shortest_path
next_current = next_temporary
pred_current, pred_other = pred_other, pred_current
dist_current, dist_other = dist_other, dist_current
next_current, next_other = next_other, next_current
out = -out
return []
def bidirectional_dijkstra(self, x, y):
r"""
Returns the shortest path between ``x`` and ``y`` using a
bidirectional version of Dijkstra's algorithm.
INPUT:
- ``x`` -- the starting vertex in the shortest path from ``x`` to
``y``.
- ``y`` -- the end vertex in the shortest path from ``x`` to ``y``.
OUTPUT:
- A list of vertices in the shortest path from ``x`` to ``y``.
EXAMPLE::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: for (u,v) in G.edges(labels=None):
... G.set_edge_label(u,v,1)
sage: G.shortest_path(0, 1, by_weight=True)
[0, 1]
TEST:
Bugfix from #7673 ::
sage: G = Graph(implementation="networkx")
sage: G.add_edges([(0,1,9),(0,2,8),(1,2,7)])
sage: Gc = G.copy(implementation='c_graph')
sage: sp = G.shortest_path_length(0,1,by_weight=True)
sage: spc = Gc.shortest_path_length(0,1,by_weight=True)
sage: sp == spc
True
"""
if x == y:
return 0
from heapq import heappush, heappop
cdef int x_int = get_vertex(x,
self.vertex_ints,
self.vertex_labels,
self._cg)
cdef int y_int = get_vertex(y,
self.vertex_ints,
self.vertex_labels,
self._cg)
cdef int u = 0
cdef int v = 0
cdef int w = 0
cdef int pred
cdef float distance
cdef float edge_label
cdef int side
cdef float f_tmp
cdef object v_obj
cdef object w_obj
cdef dict pred_x = {}
cdef dict pred_y = {}
cdef dict pred_current
cdef dict pred_other
cdef dict dist_x = {}
cdef dict dist_y = {}
cdef dict dist_current
cdef dict dist_other
cdef list queue = [(0, 1, x_int, x_int), (0, -1, y_int, y_int)]
cdef list neighbors
cdef list shortest_path = []
cdef int meeting_vertex = -1
cdef float shortest_path_length
while queue:
(distance, side, pred, v) = heappop(queue)
if meeting_vertex != -1 and distance > shortest_path_length:
break
if side == 1:
dist_current, dist_other = dist_x, dist_y
pred_current, pred_other = pred_x, pred_y
else:
dist_current, dist_other = dist_y, dist_x
pred_current, pred_other = pred_y, pred_x
if v not in dist_current:
pred_current[v] = pred
dist_current[v] = distance
if v in dist_other:
f_tmp = distance + dist_other[v]
if meeting_vertex == -1 or f_tmp < shortest_path_length:
meeting_vertex = v
shortest_path_length = f_tmp
if side == 1:
neighbors = self._cg.out_neighbors(v)
elif self._cg_rev is not None:
neighbors = self._cg_rev.out_neighbors(v)
else:
neighbors = self._cg.in_neighbors(v)
for w in neighbors:
if w not in dist_current:
v_obj = vertex_label(v, self.vertex_ints, self.vertex_labels, self._cg)
w_obj = vertex_label(w, self.vertex_ints, self.vertex_labels, self._cg)
edge_label = self.get_edge_label(v_obj, w_obj) if side == 1 else self.get_edge_label(w_obj, v_obj)
heappush(queue, (distance + edge_label, side, v, w))
if meeting_vertex == -1:
return []
else:
w = meeting_vertex
while w != x_int:
shortest_path.append(
vertex_label(w,
self.vertex_ints,
self.vertex_labels,
self._cg))
w = pred_x[w]
shortest_path.append(x)
shortest_path.reverse()
if meeting_vertex == y_int:
return shortest_path
w = pred_y[meeting_vertex]
while w != y_int:
shortest_path.append(
vertex_label(w,
self.vertex_ints,
self.vertex_labels,
self._cg))
w = pred_y[w]
shortest_path.append(y)
return shortest_path
def shortest_path_all_vertices(self, v, cutoff=None):
r"""
Returns for each vertex ``u`` a shortest ``v-u`` path.
INPUT:
- ``v`` -- a starting vertex in the shortest path.
- ``cutoff`` -- maximal distance. Longer paths will not be returned.
OUTPUT:
- A list which associates to each vertex ``u`` the shortest path
between ``u`` and ``v`` if there is one.
.. NOTE::
The weight of edges is not taken into account.
ALGORITHM:
This is just a breadth-first search.
EXAMPLES:
On the Petersen Graph::
sage: g = graphs.PetersenGraph()
sage: paths = g._backend.shortest_path_all_vertices(0)
sage: all([ len(paths[v]) == 0 or len(paths[v])-1 == g.distance(0,v) for v in g])
True
On a disconnected graph ::
sage: g = 2*graphs.RandomGNP(20,.3)
sage: paths = g._backend.shortest_path_all_vertices(0)
sage: all([ (not paths.has_key(v) and g.distance(0,v) == +Infinity) or len(paths[v])-1 == g.distance(0,v) for v in g])
True
"""
cdef list current_layer
cdef list next_layer
cdef bitset_t seen
cdef int v_int
cdef int u_int
cdef dict distances_int
cdef dict distance
cdef int d
distances = {}
d = 0
v_int = get_vertex(v, self.vertex_ints, self.vertex_labels, self._cg)
bitset_init(seen, (<CGraph>self._cg).active_vertices.size)
bitset_set_first_n(seen, 0)
bitset_add(seen, v_int)
current_layer = [(u_int, v_int)
for u_int in self._cg.out_neighbors(v_int)]
next_layer = []
distances[v] = [v]
while current_layer:
if cutoff is not None and d >= cutoff:
break
while current_layer:
v_int, u_int = current_layer.pop()
if bitset_not_in(seen, v_int):
bitset_add(seen, v_int)
distances[vertex_label(v_int, self.vertex_ints, self.vertex_labels, self._cg)] = distances[vertex_label(u_int, self.vertex_ints, self.vertex_labels, self._cg)] + [vertex_label(v_int, self.vertex_ints, self.vertex_labels, self._cg)]
next_layer.extend([(u_int, v_int) for u_int in self._cg.out_neighbors(v_int)])
current_layer = next_layer
next_layer = []
d += 1
bitset_free(seen)
return distances
def depth_first_search(self, v, reverse=False, ignore_direction=False):
r"""
Returns a depth-first search from vertex ``v``.
INPUT:
- ``v`` -- a vertex from which to start the depth-first search.
- ``reverse`` -- boolean (default: ``False``). This is only relevant
to digraphs. If this is a digraph, consider the reversed graph in
which the out-neighbors become the in-neighbors and vice versa.
- ``ignore_direction`` -- boolean (default: ``False``). This is only
relevant to digraphs. If this is a digraph, ignore all orientations
and consider the graph as undirected.
ALGORITHM:
Below is a general template for depth-first search.
- **Input:** A directed or undirected graph `G = (V, E)` of order
`n > 0`. A vertex `s` from which to start the search. The vertices
are numbered from 1 to `n = |V|`, i.e. `V = \{1, 2, \dots, n\}`.
- **Output:** A list `D` of distances of all vertices from `s`. A
tree `T` rooted at `s`.
#. `S \leftarrow [s]` # a stack of nodes to visit
#. `D \leftarrow [\infty, \infty, \dots, \infty]` # `n` copies of `\infty`
#. `D[s] \leftarrow 0`
#. `T \leftarrow [\,]`
#. while `\text{length}(S) > 0` do
#. `v \leftarrow \text{pop}(S)`
#. for each `w \in \text{adj}(v)` do # for digraphs, use out-neighbor set `\text{oadj}(v)`
#. if `D[w] = \infty` then
#. `D[w] \leftarrow D[v] + 1`
#. `\text{push}(S, w)`
#. `\text{append}(T, vw)`
#. return `(D, T)`
.. SEEALSO::
- :meth:`breadth_first_search`
-- breadth-first search for fast compiled graphs.
- :meth:`breadth_first_search <sage.graphs.generic_graph.GenericGraph.breadth_first_search>`
-- breadth-first search for generic graphs.
- :meth:`depth_first_search <sage.graphs.generic_graph.GenericGraph.depth_first_search>`
-- depth-first search for generic graphs.
EXAMPLES:
Traversing the Petersen graph using depth-first search::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: list(G.depth_first_search(0))
[0, 5, 8, 6, 9, 7, 2, 3, 4, 1]
Visiting German cities using depth-first search::
sage: G = Graph({"Mannheim": ["Frankfurt","Karlsruhe"],
... "Frankfurt": ["Mannheim","Wurzburg","Kassel"],
... "Kassel": ["Frankfurt","Munchen"],
... "Munchen": ["Kassel","Nurnberg","Augsburg"],
... "Augsburg": ["Munchen","Karlsruhe"],
... "Karlsruhe": ["Mannheim","Augsburg"],
... "Wurzburg": ["Frankfurt","Erfurt","Nurnberg"],
... "Nurnberg": ["Wurzburg","Stuttgart","Munchen"],
... "Stuttgart": ["Nurnberg"],
... "Erfurt": ["Wurzburg"]}, implementation="c_graph")
sage: list(G.depth_first_search("Frankfurt"))
['Frankfurt', 'Wurzburg', 'Nurnberg', 'Munchen', 'Kassel', 'Augsburg', 'Karlsruhe', 'Mannheim', 'Stuttgart', 'Erfurt']
"""
return Search_iterator(self,
v,
direction=-1,
reverse=reverse,
ignore_direction=ignore_direction)
def breadth_first_search(self, v, reverse=False, ignore_direction=False):
r"""
Returns a breadth-first search from vertex ``v``.
INPUT:
- ``v`` -- a vertex from which to start the breadth-first search.
- ``reverse`` -- boolean (default: ``False``). This is only relevant
to digraphs. If this is a digraph, consider the reversed graph in
which the out-neighbors become the in-neighbors and vice versa.
- ``ignore_direction`` -- boolean (default: ``False``). This is only
relevant to digraphs. If this is a digraph, ignore all orientations
and consider the graph as undirected.
ALGORITHM:
Below is a general template for breadth-first search.
- **Input:** A directed or undirected graph `G = (V, E)` of order
`n > 0`. A vertex `s` from which to start the search. The vertices
are numbered from 1 to `n = |V|`, i.e. `V = \{1, 2, \dots, n\}`.
- **Output:** A list `D` of distances of all vertices from `s`. A
tree `T` rooted at `s`.
#. `Q \leftarrow [s]` # a queue of nodes to visit
#. `D \leftarrow [\infty, \infty, \dots, \infty]` # `n` copies of `\infty`
#. `D[s] \leftarrow 0`
#. `T \leftarrow [\,]`
#. while `\text{length}(Q) > 0` do
#. `v \leftarrow \text{dequeue}(Q)`
#. for each `w \in \text{adj}(v)` do # for digraphs, use out-neighbor set `\text{oadj}(v)`
#. if `D[w] = \infty` then
#. `D[w] \leftarrow D[v] + 1`
#. `\text{enqueue}(Q, w)`
#. `\text{append}(T, vw)`
#. return `(D, T)`
.. SEEALSO::
- :meth:`breadth_first_search <sage.graphs.generic_graph.GenericGraph.breadth_first_search>`
-- breadth-first search for generic graphs.
- :meth:`depth_first_search <sage.graphs.generic_graph.GenericGraph.depth_first_search>`
-- depth-first search for generic graphs.
- :meth:`depth_first_search`
-- depth-first search for fast compiled graphs.
EXAMPLES:
Breadth-first search of the Petersen graph starting at vertex 0::
sage: G = Graph(graphs.PetersenGraph(), implementation="c_graph")
sage: list(G.breadth_first_search(0))
[0, 1, 4, 5, 2, 6, 3, 9, 7, 8]
Visiting German cities using breadth-first search::
sage: G = Graph({"Mannheim": ["Frankfurt","Karlsruhe"],
... "Frankfurt": ["Mannheim","Wurzburg","Kassel"],
... "Kassel": ["Frankfurt","Munchen"],
... "Munchen": ["Kassel","Nurnberg","Augsburg"],
... "Augsburg": ["Munchen","Karlsruhe"],
... "Karlsruhe": ["Mannheim","Augsburg"],
... "Wurzburg": ["Frankfurt","Erfurt","Nurnberg"],
... "Nurnberg": ["Wurzburg","Stuttgart","Munchen"],
... "Stuttgart": ["Nurnberg"],
... "Erfurt": ["Wurzburg"]}, implementation="c_graph")
sage: list(G.breadth_first_search("Frankfurt"))
['Frankfurt', 'Mannheim', 'Kassel', 'Wurzburg', 'Karlsruhe', 'Munchen', 'Erfurt', 'Nurnberg', 'Augsburg', 'Stuttgart']
"""
return Search_iterator(self,
v,
direction=0,
reverse=reverse,
ignore_direction=ignore_direction)
def is_connected(self):
r"""
Returns whether the graph is connected.
EXAMPLES:
Petersen's graph is connected::
sage: DiGraph(graphs.PetersenGraph(),implementation="c_graph").is_connected()
True
While the disjoint union of two of them is not::
sage: DiGraph(2*graphs.PetersenGraph(),implementation="c_graph").is_connected()
False
A graph with non-integer vertex labels::
sage: Graph(graphs.CubeGraph(3), implementation='c_graph').is_connected()
True
"""
cdef int v_int
cdef CGraph cg = <CGraph> self._cg
if cg.num_edges() < cg.num_verts - 1:
return False
v_int = bitset_first(cg.active_vertices)
if v_int == -1:
return True
v = vertex_label(v_int, self.vertex_ints, self.vertex_labels, cg)
return len(list(self.depth_first_search(v, ignore_direction=True))) == cg.num_verts
def is_strongly_connected(self):
r"""
Returns whether the graph is strongly connected.
EXAMPLES:
The circuit on 3 vertices is obviously strongly connected::
sage: g = DiGraph({0: [1], 1: [2], 2: [0]}, implementation="c_graph")
sage: g.is_strongly_connected()
True
But a transitive triangle is not::
sage: g = DiGraph({0: [1,2], 1: [2]}, implementation="c_graph")
sage: g.is_strongly_connected()
False
"""
cdef int v_int = 0
v_int = bitset_first((<CGraph>self._cg).active_vertices)
if v_int == -1:
return True
v = vertex_label(v_int, self.vertex_ints, self.vertex_labels, self._cg)
return (<CGraph>self._cg).num_verts == len(list(self.depth_first_search(v))) and \
(<CGraph>self._cg).num_verts == len(list(self.depth_first_search(v, reverse=True)))
def strongly_connected_component_containing_vertex(self, v):
r"""
Returns the strongly connected component containing the given vertex.
INPUT:
- ``v`` -- a vertex
EXAMPLES:
The digraph obtained from the ``PetersenGraph`` has an unique
strongly connected component::
sage: g = DiGraph(graphs.PetersenGraph())
sage: g.strongly_connected_component_containing_vertex(0)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
In the Butterfly DiGraph, each vertex is a strongly connected
component::
sage: g = digraphs.ButterflyGraph(3)
sage: all([[v] == g.strongly_connected_component_containing_vertex(v) for v in g])
True
"""
cdef int v_int = get_vertex(v,
self.vertex_ints,
self.vertex_labels,
self._cg)
cdef set a = set(self.depth_first_search(v))
cdef set b = set(self.depth_first_search(v, reverse=True))
return list(a & b)
def is_directed_acyclic(self, certificate = False):
r"""
Returns whether the graph is both directed and acylic (possibly with a
certificate)
INPUT:
- ``certificate`` -- whether to return a certificate (``False`` by
default).
OUTPUT:
When ``certificate=False``, returns a boolean value. When
``certificate=True`` :
* If the graph is acyclic, returns a pair ``(True, ordering)`` where
``ordering`` is a list of the vertices such that ``u`` appears
before ``v`` in ``ordering`` if ``u, v`` is an edge.
* Else, returns a pair ``(False, cycle)`` where ``cycle`` is a list
of vertices representing a circuit in the graph.
ALGORITHM:
We pick a vertex at random, think hard and find out that that if we are
to remove the vertex from the graph we must remove all of its
out-neighbors in the first place. So we put all of its out-neighbours in
a stack, and repeat the same procedure with the vertex on top of the
stack (when a vertex on top of the stack has no out-neighbors, we remove
it immediately). Of course, for each vertex we only add its outneighbors
to the end of the stack once : if for some reason the previous algorithm
leads us to do it twice, it means we have found a circuit.
We keep track of the vertices whose out-neighborhood has been added to
the stack once with a variable named ``tried``.
There is no reason why the graph should be empty at the end of this
procedure, so we run it again on the remaining vertices until none are
left or a circuit is found.
.. NOTE::
The graph is assumed to be directed. An exception is raised if it is
not.
EXAMPLES:
At first, the following graph is acyclic::
sage: D = DiGraph({ 0:[1,2,3], 4:[2,5], 1:[8], 2:[7], 3:[7], 5:[6,7], 7:[8], 6:[9], 8:[10], 9:[10] })
sage: D.plot(layout='circular').show()
sage: D.is_directed_acyclic()
True
Adding an edge from `9` to `7` does not change it::
sage: D.add_edge(9,7)
sage: D.is_directed_acyclic()
True
We can obtain as a proof an ordering of the vertices such that `u`
appears before `v` if `uv` is an edge of the graph::
sage: D.is_directed_acyclic(certificate = True)
(True, [4, 5, 6, 9, 0, 1, 2, 3, 7, 8, 10])
Adding an edge from 7 to 4, though, makes a difference::
sage: D.add_edge(7,4)
sage: D.is_directed_acyclic()
False
Indeed, it creates a circuit `7, 4, 5`::
sage: D.is_directed_acyclic(certificate = True)
(False, [7, 4, 5])
Checking acyclic graphs are indeed acyclic ::
sage: def random_acyclic(n, p):
... g = graphs.RandomGNP(n, p)
... h = DiGraph()
... h.add_edges([ ((u,v) if u<v else (v,u)) for u,v,_ in g.edges() ])
... return h
...
sage: all( random_acyclic(100, .2).is_directed_acyclic() # long time
... for i in range(50)) # long time
True
"""
if not self._directed:
raise ValueError("Input must be a directed graph.")
cdef bitset_t activated
bitset_init(activated, (<CGraph>self._cg).active_vertices.size)
bitset_set_first_n(activated, (<CGraph>self._cg).active_vertices.size)
cdef bitset_t tried
bitset_init(tried, (<CGraph>self._cg).active_vertices.size)
bitset_set_first_n(tried, 0)
cdef dict parent = {}
cdef list stack = []
cdef list ordering = []
cdef list cycle
for v in (<CGraph>self._cg).verts():
if bitset_not_in(activated, v):
continue
stack = [v]
while stack:
u = stack[-1]
if bitset_not_in(activated, u):
stack.pop(-1)
continue
if bitset_in(tried, u):
ordering.insert(0, vertex_label(u, self.vertex_ints, self.vertex_labels, self._cg))
bitset_discard(tried, u)
bitset_discard(activated, u)
stack.pop(-1)
continue
bitset_add(tried, u)
for uu in self._cg.out_neighbors(u):
if bitset_not_in(tried, uu):
if bitset_in(activated, uu):
parent[uu] = u
stack.append(uu)
else:
bitset_free(activated)
bitset_free(tried)
if not certificate:
return False
cycle = [vertex_label(u, self.vertex_ints, self.vertex_labels, self._cg)]
tmp = u
while u != uu:
u = parent.get(u,uu)
cycle.append(vertex_label(u, self.vertex_ints, self.vertex_labels, self._cg))
cycle.reverse()
return (False, cycle)
bitset_free(activated)
bitset_free(tried)
if certificate:
return (True, ordering)
else:
return True
cdef class Search_iterator:
r"""
An iterator for traversing a (di)graph.
This class is commonly used to perform a depth-first or breadth-first
search. The class does not build all at once in memory the whole list of
visited vertices. The class maintains the following variables:
- ``graph`` -- a graph whose vertices are to be iterated over.
- ``direction`` -- integer; this determines the position at which
vertices to be visited are removed from the list ``stack``. For
breadth-first search (BFS), element removal occurs at the start of the
list, as signified by the value ``direction=0``. This is because in
implementations of BFS, the list of vertices to visit are usually
maintained by a queue, so element insertion and removal follow a
first-in first-out (FIFO) protocol. For depth-first search (DFS),
element removal occurs at the end of the list, as signified by the value
``direction=-1``. The reason is that DFS is usually implemented using
a stack to maintain the list of vertices to visit. Hence, element
insertion and removal follow a last-in first-out (LIFO) protocol.
- ``stack`` -- a list of vertices to visit.
- ``seen`` -- a list of vertices that are already visited.
- ``test_out`` -- boolean; whether we want to consider the out-neighbors
of the graph to be traversed. For undirected graphs, we consider both
the in- and out-neighbors. However, for digraphs we only traverse along
out-neighbors.
- ``test_in`` -- boolean; whether we want to consider the in-neighbors of
the graph to be traversed. For undirected graphs, we consider both
the in- and out-neighbors.
EXAMPLE::
sage: g = graphs.PetersenGraph()
sage: list(g.breadth_first_search(0))
[0, 1, 4, 5, 2, 6, 3, 9, 7, 8]
"""
cdef graph
cdef int direction
cdef list stack
cdef bitset_t seen
cdef bint test_out
cdef bint test_in
def __init__(self, graph, v, direction=0, reverse=False,
ignore_direction=False):
r"""
Initialize an iterator for traversing a (di)graph.
INPUT:
- ``graph`` -- a graph to be traversed.
- ``v`` -- a vertex in ``graph`` from which to start the traversal.
- ``direction`` -- integer (default: ``0``). This determines the
position at which vertices to be visited are removed from the list
``stack`` of vertices to visit. For breadth-first search (BFS),
element removal occurs at the start of the list, as signified by the
value ``direction=0``. This is because in implementations of BFS,
the list of vertices to visit are usually maintained by a queue, so
element insertion and removal follow a first-in first-out (FIFO)
protocol. For depth-first search (DFS), element removal occurs at
the end of the list, as signified by the value ``direction=-1``. The
reason is that DFS is usually implemented using a stack to maintain
the list of vertices to visit. Hence, element insertion and removal
follow a last-in first-out (LIFO) protocol.
- ``reverse`` -- boolean (default: ``False``). This is only relevant
to digraphs. If ``graph`` is a digraph, consider the reversed graph
in which the out-neighbors become the in-neighbors and vice versa.
- ``ignore_direction`` -- boolean (default: ``False``). This is only
relevant to digraphs. If ``graph`` is a digraph, ignore all
orientations and consider the graph as undirected.
EXAMPLE::
sage: g = graphs.PetersenGraph()
sage: list(g.breadth_first_search(0))
[0, 1, 4, 5, 2, 6, 3, 9, 7, 8]
TESTS:
A vertex which does not belong to the graph::
sage: list(g.breadth_first_search(-9))
Traceback (most recent call last):
...
LookupError: Vertex (-9) is not a vertex of the graph.
An empty graph::
sage: list(Graph().breadth_first_search(''))
Traceback (most recent call last):
...
LookupError: Vertex ('') is not a vertex of the graph.
"""
self.graph = graph
self.direction = direction
bitset_init(self.seen, (<CGraph>self.graph._cg).active_vertices.size)
bitset_set_first_n(self.seen, 0)
cdef int v_id = get_vertex(v,
self.graph.vertex_ints,
self.graph.vertex_labels,
self.graph._cg)
if v_id == -1:
raise LookupError("Vertex ({0}) is not a vertex of the graph.".format(repr(v)))
self.stack = [v_id]
if not self.graph.directed:
ignore_direction = False
self.test_out = (not reverse) or ignore_direction
self.test_in = reverse or ignore_direction
def __iter__(self):
r"""
Return an iterator object over a traversal of a graph.
EXAMPLE::
sage: g = graphs.PetersenGraph()
sage: g.breadth_first_search(0)
<generator object breadth_first_search at ...
"""
return self
def __next__(self):
r"""
Return the next vertex in a traversal of a graph.
EXAMPLE::
sage: g = graphs.PetersenGraph()
sage: g.breadth_first_search(0)
<generator object breadth_first_search at ...
sage: g.breadth_first_search(0).next()
0
"""
cdef int v_int
cdef int w_int
while self.stack:
v_int = self.stack.pop(self.direction)
if bitset_not_in(self.seen, v_int):
value = vertex_label(v_int,
self.graph.vertex_ints,
self.graph.vertex_labels,
self.graph._cg)
bitset_add(self.seen, v_int)
if self.test_out:
self.stack.extend(self.graph._cg.out_neighbors(v_int))
if self.test_in:
self.stack.extend(self.graph._cg_rev.out_neighbors(v_int))
break
else:
bitset_free(self.seen)
raise StopIteration
return value
