Hi, is there a way to get the embedding? for instance as a list of faces where each face is a list as well of its vertices?
Some time ago I had a code to get it from the original boyer code:
For some reason in this new version I am unable: I am putting the code I used:
Is there a way to do the same here ?
def is_planar_nx(G, set_embedding=True):
"""
Calls Boyer's planarity algorithm to determine whether g is
planar.
"""
# First take care of a trivial case. We ignore the set_pos,
# set_embedding
if G.size() == 0: return True
# relabel vertices to the set {0,...,n-1}
cdef list vertices, adjacency_list
cdef dict embedding
cdef int status, m, n, i, j
cdef graphP theGraph
theGraph = gp_New()
status = gp_InitGraph(theGraph, G.order())
if status != OK:
raise RuntimeError("gp_InitGraph status is not ok.")
vertices = sorted(G.nodes())
for u, v in G.edges():
m, n = vertices.index(u), vertices.index(v)
status = gp_AddEdge(theGraph, m + 1, 0, n + 1, 0)
if status == NOTOK:
raise RuntimeError("gp_AddEdge status is not ok.")
elif status == NONEMBEDDABLE:
return False
status = gp_Embed(theGraph, EMBEDFLAGS_PLANAR)
if status == NOTOK:
gp_Free(&theGraph)
raise RuntimeError("Status is not ok.")
if status == NONEMBEDDABLE:
gp_Free(&theGraph)
return False
if not set_embedding:
gp_Free(&theGraph)
return True
gp_SortVertices(theGraph)
embedding = dict()
for i from 1 <= i < theGraph.N + 1:
adjacency_list = list()
j = theGraph.V[i].link[0] # the first edge
while j >= 1:
adjacency_list.append(vertices[theGraph.E[j].neighbor - 1])
j = theGraph.E[j].link[0] # the next edge
embedding[vertices[i - 1]] = adjacency_list
G.embedding = embedding
gp_Free(&theGraph)
return True
And then:
def face_list(self):
"""
List the faces of Graph (returned as a list of lists of edges (tuples) of
the current embedding.
"""
if not self.embedding:
self.is_planar() # get an embedding
# Establish set of possible edges
edgeset = set(map(tuple, self.edges))
edgeset |= set(map(tuple, list(map(reversed, edgeset))))
# Storage for face paths
path = [edgeset.pop()]
faces_sets = []
# Trace faces
while len(edgeset) > 0:
neighbors = self.embedding[path[-1][-1]]
next_node = neighbors[(neighbors.index(path[-1][-2]) + 1) % (len(neighbors))]
tup = (path[-1][-1], next_node)
if tup == path[0]:
faces_sets.append(set(map(frozenset, path)))
path = [edgeset.pop()]
else:
path.append(tup)
edgeset.discard(tup)
if len(path):
faces_sets.append(set(map(frozenset, path)))
return faces_sets
Hi, is there a way to get the embedding? for instance as a list of faces where each face is a list as well of its vertices?
Some time ago I had a code to get it from the original boyer code:
For some reason in this new version I am unable: I am putting the code I used:
Is there a way to do the same here ?
And then: