1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
|
from collections import defaultdict
import numpy as np
from numpy.testing import assert_array_almost_equal
from sklearn.utils.graph import (graph_shortest_path,
single_source_shortest_path_length)
def floyd_warshall_slow(graph, directed=False):
N = graph.shape[0]
#set nonzero entries to infinity
graph[np.where(graph == 0)] = np.inf
#set diagonal to zero
graph.flat[::N + 1] = 0
if not directed:
graph = np.minimum(graph, graph.T)
for k in range(N):
for i in range(N):
for j in range(N):
graph[i, j] = min(graph[i, j], graph[i, k] + graph[k, j])
graph[np.where(np.isinf(graph))] = 0
return graph
def generate_graph(N=20):
#sparse grid of distances
rng = np.random.RandomState(0)
dist_matrix = rng.random_sample((N, N))
#make symmetric: distances are not direction-dependent
dist_matrix = dist_matrix + dist_matrix.T
#make graph sparse
i = (rng.randint(N, size=N * N // 2), rng.randint(N, size=N * N // 2))
dist_matrix[i] = 0
#set diagonal to zero
dist_matrix.flat[::N + 1] = 0
return dist_matrix
def test_floyd_warshall():
dist_matrix = generate_graph(20)
for directed in (True, False):
graph_FW = graph_shortest_path(dist_matrix, directed, 'FW')
graph_py = floyd_warshall_slow(dist_matrix.copy(), directed)
assert_array_almost_equal(graph_FW, graph_py)
def test_dijkstra():
dist_matrix = generate_graph(20)
for directed in (True, False):
graph_D = graph_shortest_path(dist_matrix, directed, 'D')
graph_py = floyd_warshall_slow(dist_matrix.copy(), directed)
assert_array_almost_equal(graph_D, graph_py)
def test_shortest_path():
dist_matrix = generate_graph(20)
# We compare path length and not costs (-> set distances to 0 or 1)
dist_matrix[dist_matrix != 0] = 1
for directed in (True, False):
if not directed:
dist_matrix = np.minimum(dist_matrix, dist_matrix.T)
graph_py = floyd_warshall_slow(dist_matrix.copy(), directed)
for i in range(dist_matrix.shape[0]):
# Non-reachable nodes have distance 0 in graph_py
dist_dict = defaultdict(int)
dist_dict.update(single_source_shortest_path_length(dist_matrix,
i))
for j in range(graph_py[i].shape[0]):
assert_array_almost_equal(dist_dict[j], graph_py[i, j])
def test_dijkstra_bug_fix():
X = np.array([[0., 0., 4.],
[1., 0., 2.],
[0., 5., 0.]])
dist_FW = graph_shortest_path(X, directed=False, method='FW')
dist_D = graph_shortest_path(X, directed=False, method='D')
assert_array_almost_equal(dist_D, dist_FW)
|
