### view env/lib/python3.9/site-packages/networkx/generators/tests/test_expanders.py @ 0:4f3585e2f14bdraftdefaulttip

"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author shellac Mon, 22 Mar 2021 18:12:50 +0000
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```
"""Unit tests for the :mod:`networkx.generators.expanders` module.

"""

import networkx as nx
from networkx import adjacency_matrix
from networkx import number_of_nodes
from networkx.generators.expanders import chordal_cycle_graph
from networkx.generators.expanders import margulis_gabber_galil_graph
from networkx.generators.expanders import paley_graph

import pytest

def test_margulis_gabber_galil_graph():
for n in 2, 3, 5, 6, 10:
g = margulis_gabber_galil_graph(n)
assert number_of_nodes(g) == n * n
for node in g:
assert g.degree(node) == 8
assert len(node) == 2
for i in node:
assert int(i) == i
assert 0 <= i < n

np = pytest.importorskip("numpy")
scipy = pytest.importorskip("scipy")
scipy.linalg = pytest.importorskip("scipy.linalg")
# Eigenvalues are already sorted using the scipy eigvalsh,
# but the implementation in numpy does not guarantee order.
w = sorted(scipy.linalg.eigvalsh(adjacency_matrix(g).A))
assert w[-2] < 5 * np.sqrt(2)

def test_chordal_cycle_graph():
"""Test for the :func:`networkx.chordal_cycle_graph` function."""
primes = [3, 5, 7, 11]
for p in primes:
G = chordal_cycle_graph(p)
assert len(G) == p
# TODO The second largest eigenvalue should be smaller than a constant,
# independent of the number of nodes in the graph:
#
#     eigs = sorted(scipy.linalg.eigvalsh(adjacency_matrix(G).A))
#     assert_less(eigs[-2], ...)
#

def test_paley_graph():
"""Test for the :func:`networkx.paley_graph` function."""
primes = [3, 5, 7, 11, 13]
for p in primes:
G = paley_graph(p)
# G has p nodes
assert len(G) == p
# G is (p-1)/2-regular
in_degrees = {G.in_degree(node) for node in G.nodes}
out_degrees = {G.out_degree(node) for node in G.nodes}
assert len(in_degrees) == 1 and in_degrees.pop() == (p - 1) // 2
assert len(out_degrees) == 1 and out_degrees.pop() == (p - 1) // 2

# If p = 1 mod 4, -1 is a square mod 4 and therefore the
# edge in the Paley graph are symmetric.
if p % 4 == 1:
for (u, v) in G.edges:
assert (v, u) in G.edges

def test_margulis_gabber_galil_graph_badinput():
pytest.raises(nx.NetworkXError, margulis_gabber_galil_graph, 3, nx.DiGraph())
pytest.raises(nx.NetworkXError, margulis_gabber_galil_graph, 3, nx.Graph())
```