def solve_lp(graph):
points = range(graph.n)
lines = graph.lines
gamma_lp = set_up_model("connected_components_lp_2d")
connected_components = graph.connected_components
len_ccs = len(connected_components)
edges = list(graph.edges.iter_subset(points))
x = {}
for (p, q) in edges:
x[p, q] = gamma_lp.addVar(name='edge|%s - %s|' % (p, q))
t = gamma_lp.addVar(obj=1.0)
gamma_lp.modelSense = grb.GRB.MINIMIZE
gamma_lp.update()
# correct number of edges
gamma_lp.addConstr(quicksum(x[i, j] for (i, j) in edges) == (len_ccs - 1))
# crossing number range:
#gamma_lp.addConstr(0 <= t <= math.sqrt(graph.n))
# crossing constraints
for line in lines:
s = quicksum(x[p, q] for (p, q) in edges if has_crossing(line,
graph.get_line_segment(p, q)))
if s != 0.0:
gamma_lp.addConstr(
s <= t)
# connectivity constraint
for cc1 in connected_components:
gamma_lp.addConstr(quicksum(x[p, q] for (p, q) in edges if p < q and
p in cc1 and q not in cc1) +
quicksum(x[q, p] for (q, p) in edges if p > q and
p in cc1 and q not in cc1)
>= 1.)
gamma_lp.optimize()
if gamma_lp.status == grb.GRB.status.OPTIMAL:
add_best_edge(graph, x)
return
else:
format_string = 'Vars:\n'
for var in gamma_lp.getVars():
format_string += "%s\n" % var
print "number of lines = %s" % len(graph.lines)
print '%s\nlp model=%s' % (format_string, gamma_lp)
import spanningtree.plotting
spanningtree.plotting.plot(graph)
raise StandardError('Model infeasible')
def solve_lp_and_round(graph, points):
'''
creates a Gurobi model for Sariel LP formulation and round it
deterministically
return the selection of edges that are in the fractional solution
'''
lines = graph.lines
gamma_lp = set_up_model("sariels_lp_2d")
n = len(points)
edges = list(graph.edges.iter_subset(points))
x = {}
for (p, q) in edges:
x[p, q] = gamma_lp.addVar(obj=graph.euclidean_distance(p, q),
name='edge|%s - %s|' % (p, q))
t = gamma_lp.addVar(obj=1.0)
gamma_lp.modelSense = grb.GRB.MINIMIZE
gamma_lp.update()
# crossing number range:
gamma_lp.addConstr(0 <= t <= math.sqrt(n))
# crossing constraints
for line in lines:
s = quicksum(x[p, q] for (p, q) in edges if has_crossing(line,
graph.get_line_segment(p, q)))
if s != 0.0:
gamma_lp.addConstr(
s <= t)
# connectivity constraint
for p in points:
gamma_lp.addConstr(
quicksum(x[p, q] for q in points if p < q) +
quicksum(x[q, p] for q in points if p > q)
>= 1)
gamma_lp.optimize()
if gamma_lp.status == grb.GRB.status.OPTIMAL:
round_solution = []
for (p, q) in edges:
val = x[p, q].X
sample = random.random()
if sample <= val:
graph.solution.update(p, q, True)
round_solution.append((p, q))
return round_solution
def find_min_edge(graph, line_weights):
'''
search for the minimum weight edge between two connected components with
lowest crossing weight
'''
weights = {}
for edge in graph.edges:
(p, q) = edge
line_segment = graph.get_line_segment(p, q)
weights[edge] = 0.0
for line in graph.lines:
if crossing.has_crossing(line, line_segment):
weights[edge] += line_weights[line]
min_edge = min(weights, key=weights.get)
(p, q) = min_edge
assert p < q
return min_edge
def test_has_crossing(self):
line = HighDimLine(np.array([(3., 2), (5., 0)])) # y = -x + 5
line_segment = HighDimLineSegment(
np.array([(3, 0.5), (5, 1.5)])) # y = 0.5 x - 1
# line_points[0] = segpoints[0] = intersection point
line_points = np.array([(4., 1.), (5., 0.)])
self.assertTrue(line.is_on(line_points[0]))
self.assertTrue(line.is_on(line_points[1]))
seg_points = np.copy(line_points)
seg_points[1, 1] = 1.5
self.assertTrue(line_segment.is_on(seg_points[0]))
self.assertTrue(line_segment.is_on(seg_points[1]))
line_val = line.call(np.array([5.]))
np_assert_allclose(0.0, line_val)
np_assert_allclose(line_points[..., -1], line(line_points[..., :-1]))
self.assertTrue(has_crossing(line, line_segment))
def create_lp(graph):
'''
create a gurobi model containing LP formulation like that in the Fekete
paper
'''
lambda_lp = set_up_model("fekete_lp_2d")
#lambda_lp.setParam('Cuts', 3)
n = graph.n
edges = graph.edges
for (p, q) in edges:
x[p, q] = lambda_lp.addVar(name='edge|%s - %s|' % (p, q))
t = lambda_lp.addVar(obj=1.0)
lambda_lp.modelSense = grb.GRB.MINIMIZE
lambda_lp.update()
# correct number of edges
lambda_lp.addConstr(quicksum(x[i, j] for (i, j) in edges) == (n - 1))
# subsets = nonempty_subsets(n)
# # connectivity constraints
# for subset in subsets:
# lambda_lp.addConstr(quicksum(x[i,j] for (i,j) in cut(subset, edges))
# >= 1)
# connectivity constraint
connected_components = graph.connected_components
for cc1 in connected_components:
lambda_lp.addConstr(quicksum(x[p, q] for (p, q) in edges if p < q and
p in cc1 and q not in cc1) +
quicksum(x[q, p] for (q, p) in edges if p > q and
p in cc1 and q not in cc1)
>= 1.)
lines = graph.lines
# bound crossing number
for line in lines:
s = quicksum(x[p, q] for (p, q) in edges if crossing.has_crossing(line,
graph.get_line_segment(p, q)))
if s != 0.0:
lambda_lp.addConstr(s <= t)
return lambda_lp
def test_has_also_crossing(self):
line = HighDimLine(np.array([(3., 5.5), (5., 6.5)])) # y = 0.5x + 4
line_segment = HighDimLineSegment(
np.array([(5., 7.), (6., 4.)])) # y = -3x + 22
self.assertTrue(has_crossing(line, line_segment))
def test_has_no_crossing_line_and_segment_parallel(self):
line = HighDimLine(np.array([(3, 2), (5, 0)])) # y = -x + 5
line_segment = HighDimLineSegment(
np.array([(0, 4), (6, -2)])) # y = -x + 4
self.assertFalse(has_crossing(line, line_segment))
def test_has_no_crossing_linesegment_too_short(self):
line = HighDimLine(np.array([[3., 2], [5, 0]])) # y = -x + 5
line_segment = HighDimLineSegment(
np.array([[0., -1], [3, 0.5]])) # y = 0.5 x - 1
self.assertFalse(has_crossing(line, line_segment))
