Fixed database typo and removed unnecessary class identifier.

venv/Lib/site-packages/networkx/linalg/tests/test_bethehessian.py

@@ -0,0 +1,42 @@
+import pytest
+
+np = pytest.importorskip("numpy")
+npt = pytest.importorskip("numpy.testing")
+sp = pytest.importorskip("scipy")
+
+import networkx as nx
+from networkx.generators.degree_seq import havel_hakimi_graph
+
+
+class TestBetheHessian:
+    @classmethod
+    def setup_class(cls):
+        deg = [3, 2, 2, 1, 0]
+        cls.G = havel_hakimi_graph(deg)
+        cls.P = nx.path_graph(3)
+
+    def test_bethe_hessian(self):
+        "Bethe Hessian matrix"
+        # fmt: off
+        H = np.array([[4, -2, 0],
+                      [-2, 5, -2],
+                      [0, -2, 4]])
+        # fmt: on
+        permutation = [2, 0, 1]
+        # Bethe Hessian gives expected form
+        npt.assert_equal(nx.bethe_hessian_matrix(self.P, r=2).todense(), H)
+        # nodelist is correctly implemented
+        npt.assert_equal(
+            nx.bethe_hessian_matrix(self.P, r=2, nodelist=permutation).todense(),
+            H[np.ix_(permutation, permutation)],
+        )
+        # Equal to Laplacian matrix when r=1
+        npt.assert_equal(
+            nx.bethe_hessian_matrix(self.G, r=1).todense(),
+            nx.laplacian_matrix(self.G).todense(),
+        )
+        # Correct default for the regularizer r
+        npt.assert_equal(
+            nx.bethe_hessian_matrix(self.G).todense(),
+            nx.bethe_hessian_matrix(self.G, r=1.25).todense(),
+        )