def test_set_optimizer_to_none(self):
"""Tests that setting the optimizer to None results in the default behavior"""
vqe = VQE(
ansatz=self.ryrz_wavefunction,
optimizer=L_BFGS_B(),
quantum_instance=self.statevector_simulator,
)
vqe.optimizer = None
self.assertIsInstance(vqe.optimizer, SLSQP)
def test_vqe_optimizer(self):
"""Test running same VQE twice to re-use optimizer, then switch optimizer"""
vqe = VQE(
optimizer=SLSQP(),
quantum_instance=QuantumInstance(BasicAer.get_backend("statevector_simulator")),
)
def run_check():
result = vqe.compute_minimum_eigenvalue(operator=self.h2_op)
self.assertAlmostEqual(result.eigenvalue.real, -1.85727503, places=5)
run_check()
with self.subTest("Optimizer re-use"):
run_check()
with self.subTest("Optimizer replace"):
vqe.optimizer = L_BFGS_B()
run_check()