def bruteforce(graph):
max_size = 0
max_is = None
for subset in subsets(graph.vertices):
if size(subset) > max_size and is_independent(graph, subset):
max_is = subset
max_size = size(subset)
return max_is
def save(self, filename):
with open(filename, 'w') as f:
f.write('p edges {} {}\n'.format(size(self.vertices), len(list(self.edges))))
f.writelines(
'n {}\n'.format(index(v)) for v in self
)
f.writelines(
'e {} {}\n'.format(index(v), index(w)) for v, w in self.edges
)
def heuristic(graph):
subset = 0
while is_independent(graph, subset):
# Find valid vertex with the least new neighbors
existing_neighbors = graph(subset)
min_new_neighbors = Infinity
new_vertex = None
for v in iterate(subtract(graph.vertices, subset)):
if not graph(v) & subset:
new_neighbors = subtract(graph(v), existing_neighbors)
if size(new_neighbors) < min_new_neighbors:
min_new_neighbors = size(new_neighbors)
new_vertex = v
if new_vertex == None:
return subset
else:
subset |= new_vertex
def greedy_step(G, left, right, un_left, booldim_left, un_table, bound):
best_vertex = None
best_booldim = Infinity
best_un = None
if size(right) == 1:
return right, {0}, 1
assert size(right) > 1
candidates = get_neighborhood_2(G.neighborhoods, left) & right
# Trivial cases are slow
for v in iterate(candidates):
if trivial_case(G.neighborhoods, left, right, v):
new_un = increment_un(G, left, un_left, v)
new_booldim = len(new_un)
return v, new_un, new_booldim
for v in iterate(candidates):
if left | v not in un_table:
un_table[left | v] = increment_un(G, left, un_left, v)
new_un = un_table[left | v]
new_booldim = len(new_un)
# Apply pruning
if new_booldim >= bound:
# print('pruning')
continue
if new_booldim < best_booldim:
best_vertex = v
best_booldim = new_booldim
best_un = new_un
# If nothing found
if best_vertex == None:
best_un = increment_un(G, left, un_left, v)
best_booldim = len(best_un)
best_vertex = v
assert best_vertex != None
return best_vertex, best_un, best_booldim
def split(self, v, w):
"""Split edge between two vertices."""
if not v in self:
raise ValueError
if not w in self:
raise ValueError
if w == v:
raise ValueError('{} and {} are the same vertex.'.format(v, w))
if contains(self(v), w):
raise ValueError('{} and {} are not connected.'.format(v, w))
# Only support undirected edges
assert contains(self(w), v)
new = bit(size(self.vertices))
self.add(new)
self.disconnect(v, w)
self.connect(v, new)
self.connect(w, new)
def incremental_un_heuristic(G):
lboolw_components = []
decomposition_components = []
for component in components(G):
best_lboolw = Infinity
best_decomposition = None
for i, start in enumerate([first(component)]):
#for i, start in enumerate(iterate(component)):
print('{}th starting vertex'.format(i))
right = subtract(component, start)
left = start
un_left = increment_un(G, 0, {0}, start)
booldim_left = 1
decomposition = [start]
lboolw = len(un_left)
for _ in range(size(component) - 1):
best_vertex, best_un, _ = greedy_step(G, left, right, un_left,
booldim_left, {}, Infinity)
booldim_left = len(best_un)
lboolw = max(lboolw, booldim_left)
un_left = best_un
decomposition.append(best_vertex)
right = subtract(right, best_vertex)
left = left | best_vertex
if lboolw < best_lboolw:
best_lboolw = lboolw
best_decomposition = decomposition
lboolw_components.append(best_lboolw)
decomposition_components.append(best_decomposition)
total_lboolw = max(lboolw_components)
total_decomposition = [v for part in decomposition_components for v in part]
return total_lboolw, total_decomposition
#grid = matrix_to_dict([
#[0, 0, 5, 5, 5],
#[0, 0, 0, 1, 5],
#[2, 2, 4, 1, 5],
#[3, 2, 3, 1, 5],
#[3, 3, 3, 3, 6],
#])
while 1:
width = randint(5, 25)
height = randint(5, 25)
max_field_size = randint(5, 25)
grid = random_walk(width, height, max_field_size)
graph = PixelGraph(grid)
width, decomposition = incremental_un_heuristic(graph)
heuristic_solution = heuristic(graph)
exact_solution = from_decomposition(graph, decomposition)
if size(heuristic_solution) < size(exact_solution) / 1.2:
break
print(graph)
print(tostring(heuristic_solution))
print(tostring(exact_solution))
#Possible engines: dot, neato, fdp, sfdp, twopi, circo
plot(graph, 'neato')
#print(tostring(from_decomposition(graph, iterate(graph.vertices))))
#print(tostring(bruteforce(graph)))
def __len__(self):
"""Iterate over all vertices."""
return size(self.vertices)
def density(self):
n = size(self.vertices)
m = len(list(self.edges))
return float(2 * m) / float(n * (n - 1))
def add(collection, solution):
key = graph(solution) & right
if key not in collection or size(collection[key]) < size(solution):
collection[key] = solution
#grid = matrix_to_dict([
#[0, 0, 5, 5, 5],
#[0, 0, 0, 1, 5],
#[2, 2, 4, 1, 5],
#[3, 2, 3, 1, 5],
#[3, 3, 3, 3, 6],
#])
while 1:
width = randint(5, 35)
height = 40 - width
max_field_size = randint(5, 25)
grid = random_walk(width, height, max_field_size)
graph = PixelGraph(grid)
width, decomposition = incremental_un_heuristic(graph)
heuristic_solution = heuristic(graph)
exact_solution = from_decomposition(graph, decomposition)
if size(heuristic_solution) < size(exact_solution) - 3:
break
print(graph)
print(tostring(heuristic_solution))
print(tostring(exact_solution))
#Possible engines: dot, neato, fdp, sfdp, twopi, circo
plot(graph, 'neato')
#print(tostring(from_decomposition(graph, iterate(graph.vertices))))
#print(tostring(bruteforce(graph)))
