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Diffstat (limited to '.venv/lib/python3.12/site-packages/networkx/linalg/tests/test_algebraic_connectivity.py')
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diff --git a/.venv/lib/python3.12/site-packages/networkx/linalg/tests/test_algebraic_connectivity.py b/.venv/lib/python3.12/site-packages/networkx/linalg/tests/test_algebraic_connectivity.py new file mode 100644 index 00000000..089d917a --- /dev/null +++ b/.venv/lib/python3.12/site-packages/networkx/linalg/tests/test_algebraic_connectivity.py @@ -0,0 +1,402 @@ +from math import sqrt + +import pytest + +np = pytest.importorskip("numpy") + + +import networkx as nx + +methods = ("tracemin_pcg", "tracemin_lu", "lanczos", "lobpcg") + + +def test_algebraic_connectivity_tracemin_chol(): + """Test that "tracemin_chol" raises an exception.""" + pytest.importorskip("scipy") + G = nx.barbell_graph(5, 4) + with pytest.raises(nx.NetworkXError): + nx.algebraic_connectivity(G, method="tracemin_chol") + + +def test_fiedler_vector_tracemin_chol(): + """Test that "tracemin_chol" raises an exception.""" + pytest.importorskip("scipy") + G = nx.barbell_graph(5, 4) + with pytest.raises(nx.NetworkXError): + nx.fiedler_vector(G, method="tracemin_chol") + + +def test_spectral_ordering_tracemin_chol(): + """Test that "tracemin_chol" raises an exception.""" + pytest.importorskip("scipy") + G = nx.barbell_graph(5, 4) + with pytest.raises(nx.NetworkXError): + nx.spectral_ordering(G, method="tracemin_chol") + + +def test_fiedler_vector_tracemin_unknown(): + """Test that "tracemin_unknown" raises an exception.""" + pytest.importorskip("scipy") + G = nx.barbell_graph(5, 4) + L = nx.laplacian_matrix(G) + X = np.asarray(np.random.normal(size=(1, L.shape[0]))).T + with pytest.raises(nx.NetworkXError, match="Unknown linear system solver"): + nx.linalg.algebraicconnectivity._tracemin_fiedler( + L, X, normalized=False, tol=1e-8, method="tracemin_unknown" + ) + + +def test_spectral_bisection(): + pytest.importorskip("scipy") + G = nx.barbell_graph(3, 0) + C = nx.spectral_bisection(G) + assert C == ({0, 1, 2}, {3, 4, 5}) + + mapping = dict(enumerate("badfec")) + G = nx.relabel_nodes(G, mapping) + C = nx.spectral_bisection(G) + assert C == ( + {mapping[0], mapping[1], mapping[2]}, + {mapping[3], mapping[4], mapping[5]}, + ) + + +def check_eigenvector(A, l, x): + nx = np.linalg.norm(x) + # Check zeroness. + assert nx != pytest.approx(0, abs=1e-07) + y = A @ x + ny = np.linalg.norm(y) + # Check collinearity. + assert x @ y == pytest.approx(nx * ny, abs=1e-7) + # Check eigenvalue. + assert ny == pytest.approx(l * nx, abs=1e-7) + + +class TestAlgebraicConnectivity: + @pytest.mark.parametrize("method", methods) + def test_directed(self, method): + G = nx.DiGraph() + pytest.raises( + nx.NetworkXNotImplemented, nx.algebraic_connectivity, G, method=method + ) + pytest.raises(nx.NetworkXNotImplemented, nx.fiedler_vector, G, method=method) + + @pytest.mark.parametrize("method", methods) + def test_null_and_singleton(self, method): + G = nx.Graph() + pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G, method=method) + pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method=method) + G.add_edge(0, 0) + pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G, method=method) + pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method=method) + + @pytest.mark.parametrize("method", methods) + def test_disconnected(self, method): + G = nx.Graph() + G.add_nodes_from(range(2)) + assert nx.algebraic_connectivity(G) == 0 + pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method=method) + G.add_edge(0, 1, weight=0) + assert nx.algebraic_connectivity(G) == 0 + pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method=method) + + def test_unrecognized_method(self): + pytest.importorskip("scipy") + G = nx.path_graph(4) + pytest.raises(nx.NetworkXError, nx.algebraic_connectivity, G, method="unknown") + pytest.raises(nx.NetworkXError, nx.fiedler_vector, G, method="unknown") + + @pytest.mark.parametrize("method", methods) + def test_two_nodes(self, method): + pytest.importorskip("scipy") + G = nx.Graph() + G.add_edge(0, 1, weight=1) + A = nx.laplacian_matrix(G) + assert nx.algebraic_connectivity(G, tol=1e-12, method=method) == pytest.approx( + 2, abs=1e-7 + ) + x = nx.fiedler_vector(G, tol=1e-12, method=method) + check_eigenvector(A, 2, x) + + @pytest.mark.parametrize("method", methods) + def test_two_nodes_multigraph(self, method): + pytest.importorskip("scipy") + G = nx.MultiGraph() + G.add_edge(0, 0, spam=1e8) + G.add_edge(0, 1, spam=1) + G.add_edge(0, 1, spam=-2) + A = -3 * nx.laplacian_matrix(G, weight="spam") + assert nx.algebraic_connectivity( + G, weight="spam", tol=1e-12, method=method + ) == pytest.approx(6, abs=1e-7) + x = nx.fiedler_vector(G, weight="spam", tol=1e-12, method=method) + check_eigenvector(A, 6, x) + + def test_abbreviation_of_method(self): + pytest.importorskip("scipy") + G = nx.path_graph(8) + A = nx.laplacian_matrix(G) + sigma = 2 - sqrt(2 + sqrt(2)) + ac = nx.algebraic_connectivity(G, tol=1e-12, method="tracemin") + assert ac == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, tol=1e-12, method="tracemin") + check_eigenvector(A, sigma, x) + + @pytest.mark.parametrize("method", methods) + def test_path(self, method): + pytest.importorskip("scipy") + G = nx.path_graph(8) + A = nx.laplacian_matrix(G) + sigma = 2 - sqrt(2 + sqrt(2)) + ac = nx.algebraic_connectivity(G, tol=1e-12, method=method) + assert ac == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, tol=1e-12, method=method) + check_eigenvector(A, sigma, x) + + @pytest.mark.parametrize("method", methods) + def test_problematic_graph_issue_2381(self, method): + pytest.importorskip("scipy") + G = nx.path_graph(4) + G.add_edges_from([(4, 2), (5, 1)]) + A = nx.laplacian_matrix(G) + sigma = 0.438447187191 + ac = nx.algebraic_connectivity(G, tol=1e-12, method=method) + assert ac == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, tol=1e-12, method=method) + check_eigenvector(A, sigma, x) + + @pytest.mark.parametrize("method", methods) + def test_cycle(self, method): + pytest.importorskip("scipy") + G = nx.cycle_graph(8) + A = nx.laplacian_matrix(G) + sigma = 2 - sqrt(2) + ac = nx.algebraic_connectivity(G, tol=1e-12, method=method) + assert ac == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, tol=1e-12, method=method) + check_eigenvector(A, sigma, x) + + @pytest.mark.parametrize("method", methods) + def test_seed_argument(self, method): + pytest.importorskip("scipy") + G = nx.cycle_graph(8) + A = nx.laplacian_matrix(G) + sigma = 2 - sqrt(2) + ac = nx.algebraic_connectivity(G, tol=1e-12, method=method, seed=1) + assert ac == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, tol=1e-12, method=method, seed=1) + check_eigenvector(A, sigma, x) + + @pytest.mark.parametrize( + ("normalized", "sigma", "laplacian_fn"), + ( + (False, 0.2434017461399311, nx.laplacian_matrix), + (True, 0.08113391537997749, nx.normalized_laplacian_matrix), + ), + ) + @pytest.mark.parametrize("method", methods) + def test_buckminsterfullerene(self, normalized, sigma, laplacian_fn, method): + pytest.importorskip("scipy") + G = nx.Graph( + [ + (1, 10), + (1, 41), + (1, 59), + (2, 12), + (2, 42), + (2, 60), + (3, 6), + (3, 43), + (3, 57), + (4, 8), + (4, 44), + (4, 58), + (5, 13), + (5, 56), + (5, 57), + (6, 10), + (6, 31), + (7, 14), + (7, 56), + (7, 58), + (8, 12), + (8, 32), + (9, 23), + (9, 53), + (9, 59), + (10, 15), + (11, 24), + (11, 53), + (11, 60), + (12, 16), + (13, 14), + (13, 25), + (14, 26), + (15, 27), + (15, 49), + (16, 28), + (16, 50), + (17, 18), + (17, 19), + (17, 54), + (18, 20), + (18, 55), + (19, 23), + (19, 41), + (20, 24), + (20, 42), + (21, 31), + (21, 33), + (21, 57), + (22, 32), + (22, 34), + (22, 58), + (23, 24), + (25, 35), + (25, 43), + (26, 36), + (26, 44), + (27, 51), + (27, 59), + (28, 52), + (28, 60), + (29, 33), + (29, 34), + (29, 56), + (30, 51), + (30, 52), + (30, 53), + (31, 47), + (32, 48), + (33, 45), + (34, 46), + (35, 36), + (35, 37), + (36, 38), + (37, 39), + (37, 49), + (38, 40), + (38, 50), + (39, 40), + (39, 51), + (40, 52), + (41, 47), + (42, 48), + (43, 49), + (44, 50), + (45, 46), + (45, 54), + (46, 55), + (47, 54), + (48, 55), + ] + ) + A = laplacian_fn(G) + try: + assert nx.algebraic_connectivity( + G, normalized=normalized, tol=1e-12, method=method + ) == pytest.approx(sigma, abs=1e-7) + x = nx.fiedler_vector(G, normalized=normalized, tol=1e-12, method=method) + check_eigenvector(A, sigma, x) + except nx.NetworkXError as err: + if err.args not in ( + ("Cholesky solver unavailable.",), + ("LU solver unavailable.",), + ): + raise + + +class TestSpectralOrdering: + _graphs = (nx.Graph, nx.DiGraph, nx.MultiGraph, nx.MultiDiGraph) + + @pytest.mark.parametrize("graph", _graphs) + def test_nullgraph(self, graph): + G = graph() + pytest.raises(nx.NetworkXError, nx.spectral_ordering, G) + + @pytest.mark.parametrize("graph", _graphs) + def test_singleton(self, graph): + G = graph() + G.add_node("x") + assert nx.spectral_ordering(G) == ["x"] + G.add_edge("x", "x", weight=33) + G.add_edge("x", "x", weight=33) + assert nx.spectral_ordering(G) == ["x"] + + def test_unrecognized_method(self): + G = nx.path_graph(4) + pytest.raises(nx.NetworkXError, nx.spectral_ordering, G, method="unknown") + + @pytest.mark.parametrize("method", methods) + def test_three_nodes(self, method): + pytest.importorskip("scipy") + G = nx.Graph() + G.add_weighted_edges_from([(1, 2, 1), (1, 3, 2), (2, 3, 1)], weight="spam") + order = nx.spectral_ordering(G, weight="spam", method=method) + assert set(order) == set(G) + assert {1, 3} in (set(order[:-1]), set(order[1:])) + + @pytest.mark.parametrize("method", methods) + def test_three_nodes_multigraph(self, method): + pytest.importorskip("scipy") + G = nx.MultiDiGraph() + G.add_weighted_edges_from([(1, 2, 1), (1, 3, 2), (2, 3, 1), (2, 3, 2)]) + order = nx.spectral_ordering(G, method=method) + assert set(order) == set(G) + assert {2, 3} in (set(order[:-1]), set(order[1:])) + + @pytest.mark.parametrize("method", methods) + def test_path(self, method): + pytest.importorskip("scipy") + path = list(range(10)) + np.random.shuffle(path) + G = nx.Graph() + nx.add_path(G, path) + order = nx.spectral_ordering(G, method=method) + assert order in [path, list(reversed(path))] + + @pytest.mark.parametrize("method", methods) + def test_seed_argument(self, method): + pytest.importorskip("scipy") + path = list(range(10)) + np.random.shuffle(path) + G = nx.Graph() + nx.add_path(G, path) + order = nx.spectral_ordering(G, method=method, seed=1) + assert order in [path, list(reversed(path))] + + @pytest.mark.parametrize("method", methods) + def test_disconnected(self, method): + pytest.importorskip("scipy") + G = nx.Graph() + nx.add_path(G, range(0, 10, 2)) + nx.add_path(G, range(1, 10, 2)) + order = nx.spectral_ordering(G, method=method) + assert set(order) == set(G) + seqs = [ + list(range(0, 10, 2)), + list(range(8, -1, -2)), + list(range(1, 10, 2)), + list(range(9, -1, -2)), + ] + assert order[:5] in seqs + assert order[5:] in seqs + + @pytest.mark.parametrize( + ("normalized", "expected_order"), + ( + (False, [[1, 2, 0, 3, 4, 5, 6, 9, 7, 8], [8, 7, 9, 6, 5, 4, 3, 0, 2, 1]]), + (True, [[1, 2, 3, 0, 4, 5, 9, 6, 7, 8], [8, 7, 6, 9, 5, 4, 0, 3, 2, 1]]), + ), + ) + @pytest.mark.parametrize("method", methods) + def test_cycle(self, normalized, expected_order, method): + pytest.importorskip("scipy") + path = list(range(10)) + G = nx.Graph() + nx.add_path(G, path, weight=5) + G.add_edge(path[-1], path[0], weight=1) + A = nx.laplacian_matrix(G).todense() + order = nx.spectral_ordering(G, normalized=normalized, method=method) + assert order in expected_order |