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66 lines
2.1 KiB
Python
66 lines
2.1 KiB
Python
"""Test the minimum spanning tree function"""
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import numpy as np
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from numpy.testing import assert_
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import numpy.testing as npt
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from scipy.sparse import csr_matrix
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from scipy.sparse.csgraph import minimum_spanning_tree
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def test_minimum_spanning_tree():
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# Create a graph with two connected components.
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graph = [[0,1,0,0,0],
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[1,0,0,0,0],
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[0,0,0,8,5],
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[0,0,8,0,1],
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[0,0,5,1,0]]
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graph = np.asarray(graph)
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# Create the expected spanning tree.
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expected = [[0,1,0,0,0],
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[0,0,0,0,0],
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[0,0,0,0,5],
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[0,0,0,0,1],
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[0,0,0,0,0]]
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expected = np.asarray(expected)
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# Ensure minimum spanning tree code gives this expected output.
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csgraph = csr_matrix(graph)
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mintree = minimum_spanning_tree(csgraph)
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npt.assert_array_equal(mintree.todense(), expected,
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'Incorrect spanning tree found.')
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# Ensure that the original graph was not modified.
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npt.assert_array_equal(csgraph.todense(), graph,
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'Original graph was modified.')
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# Now let the algorithm modify the csgraph in place.
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mintree = minimum_spanning_tree(csgraph, overwrite=True)
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npt.assert_array_equal(mintree.todense(), expected,
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'Graph was not properly modified to contain MST.')
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np.random.seed(1234)
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for N in (5, 10, 15, 20):
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# Create a random graph.
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graph = 3 + np.random.random((N, N))
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csgraph = csr_matrix(graph)
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# The spanning tree has at most N - 1 edges.
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mintree = minimum_spanning_tree(csgraph)
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assert_(mintree.nnz < N)
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# Set the sub diagonal to 1 to create a known spanning tree.
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idx = np.arange(N-1)
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graph[idx,idx+1] = 1
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csgraph = csr_matrix(graph)
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mintree = minimum_spanning_tree(csgraph)
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# We expect to see this pattern in the spanning tree and otherwise
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# have this zero.
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expected = np.zeros((N, N))
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expected[idx, idx+1] = 1
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npt.assert_array_equal(mintree.todense(), expected,
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'Incorrect spanning tree found.')
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