def test_backend_change(self, user_expectation):
"""Test that VQE works when backend changes."""
vqd = VQD(
k=1,
ansatz=TwoLocal(rotation_blocks=["ry", "rz"],
entanglement_blocks="cz"),
optimizer=SLSQP(maxiter=2),
expectation=user_expectation,
quantum_instance=BasicAer.get_backend("statevector_simulator"),
)
result0 = vqd.compute_eigenvalues(operator=self.h2_op)
if user_expectation is not None:
with self.subTest("User expectation kept."):
self.assertEqual(vqd.expectation, user_expectation)
vqd.quantum_instance = BasicAer.get_backend("qasm_simulator")
# works also if no expectation is set, since it will be determined automatically
result1 = vqd.compute_eigenvalues(operator=self.h2_op)
if user_expectation is not None:
with self.subTest(
"Change backend with user expectation, it is kept."):
self.assertEqual(vqd.expectation, user_expectation)
with self.subTest("Check results."):
self.assertEqual(len(result0.optimal_point),
len(result1.optimal_point))
def test_reuse(self):
"""Test re-using a VQD algorithm instance."""
vqd = VQD(k=1)
with self.subTest(msg="assert running empty raises AlgorithmError"):
with self.assertRaises(AlgorithmError):
_ = vqd.compute_eigenvalues(operator=self.h2_op)
ansatz = TwoLocal(rotation_blocks=["ry", "rz"],
entanglement_blocks="cz")
vqd.ansatz = ansatz
with self.subTest(msg="assert missing operator raises AlgorithmError"):
with self.assertRaises(AlgorithmError):
_ = vqd.compute_eigenvalues(operator=self.h2_op)
vqd.expectation = MatrixExpectation()
vqd.quantum_instance = self.statevector_simulator
with self.subTest(msg="assert VQE works once all info is available"):
result = vqd.compute_eigenvalues(operator=self.h2_op)
np.testing.assert_array_almost_equal(result.eigenvalues.real,
self.h2_energy,
decimal=2)
operator = PrimitiveOp(
np.array([[1, 0, 0, 0], [0, -1, 0, 0], [0, 0, 2, 0], [0, 0, 0,
3]]))
with self.subTest(msg="assert minimum eigensolver interface works"):
result = vqd.compute_eigenvalues(operator=operator)
self.assertAlmostEqual(result.eigenvalues.real[0], -1.0, places=5)