def test_multiple_rx_gradient(self, tol):
"""Tests that the gradient of multiple RX gates in a circuit
yeilds the correct result."""
dev = qml.device("default.qubit", wires=3)
params = np.array([np.pi, np.pi / 2, np.pi / 3])
with ReversibleTape() as tape:
qml.RX(params[0], wires=0)
qml.RX(params[1], wires=1)
qml.RX(params[2], wires=2)
for idx in range(3):
expval(qml.PauliZ(idx))
circuit_output = tape.execute(dev)
expected_output = np.cos(params)
assert np.allclose(circuit_output, expected_output, atol=tol, rtol=0)
# circuit jacobians
circuit_jacobian = tape.jacobian(dev, method="analytic")
expected_jacobian = -np.diag(np.sin(params))
assert np.allclose(circuit_jacobian,
expected_jacobian,
atol=tol,
rtol=0)
def test_diff_circuit_construction(self, mocker):
"""Test that the diff circuit is correctly constructed"""
dev = qml.device("default.qubit", wires=2)
with ReversibleTape() as tape:
qml.PauliX(wires=0)
qml.RX(0.542, wires=0)
qml.RY(0.542, wires=0)
expval(qml.PauliZ(0))
spy = mocker.spy(dev, "execute")
tape.jacobian(dev)
tape0 = spy.call_args_list[0][0][0]
tape1 = spy.call_args_list[1][0][0]
tape2 = spy.call_args_list[2][0][0]
assert tape0 is tape
assert len(tape1.operations) == 3
assert not tape1.measurements
assert tape1.operations[0].name == "RY.inv"
assert tape1.operations[1].name == "PauliX"
assert tape1.operations[2].name == "RY"
assert len(tape2.operations) == 1
assert not tape2.measurements
assert tape2.operations[0].name == "PauliY"
def test_ry_gradient(self, par, mocker, tol):
"""Test that the gradient of the RY gate matches the exact analytic
formula. Further, make sure the correct gradient methods
are being called."""
with ReversibleTape() as tape:
qml.RY(par, wires=[0])
expval(qml.PauliX(0))
tape.trainable_params = {0}
dev = qml.device("default.qubit", wires=1)
spy_numeric = mocker.spy(tape, "numeric_pd")
spy_analytic = mocker.spy(tape, "analytic_pd")
# gradients
exact = np.cos(par)
grad_F = tape.jacobian(dev, method="numeric")
spy_numeric.assert_called()
spy_analytic.assert_not_called()
spy_device = mocker.spy(tape, "execute_device")
grad_A = tape.jacobian(dev, method="analytic")
spy_analytic.assert_called()
spy_device.assert_called_once(
) # check that the state was only pre-computed once
# different methods must agree
assert np.allclose(grad_F, exact, atol=tol, rtol=0)
assert np.allclose(grad_A, exact, atol=tol, rtol=0)
def test_probs_exception(self):
"""Tests that an exception is raised when probability
is used with the ReversibleTape."""
# TODO: remove this test when this support is added
dev = qml.device("default.qubit", wires=2)
with ReversibleTape() as tape:
qml.PauliX(wires=0)
qml.RX(0.542, wires=0)
probs(wires=[0, 1])
with pytest.raises(ValueError, match="Probability is not supported"):
tape.jacobian(dev)
def test_var_exception(self):
"""Tests that an exception is raised when variance
is used with the ReversibleTape."""
# TODO: remove this test when this support is added
dev = qml.device("default.qubit", wires=2)
with ReversibleTape() as tape:
qml.PauliX(wires=0)
qml.RX(0.542, wires=0)
var(qml.PauliZ(0))
with pytest.raises(ValueError, match="Variance is not supported"):
tape.jacobian(dev)
def test_controlled_rotation_gates_exception(self, op, name):
"""Tests that an exception is raised when a controlled
rotation gate is used with the ReversibleTape."""
# TODO: remove this test when this support is added
dev = qml.device("default.qubit", wires=2)
with ReversibleTape() as tape:
qml.PauliX(wires=0)
op(0.542, wires=[0, 1])
expval(qml.PauliZ(0))
with pytest.raises(
ValueError,
match="The {} gate is not currently supported".format(name)):
tape.jacobian(dev)
def test_phaseshift_exception(self):
"""Tests that an exception is raised when a PhaseShift gate
is used with the ReversibleTape."""
# TODO: remove this test when this support is added
dev = qml.device("default.qubit", wires=1)
with ReversibleTape() as tape:
qml.PauliX(wires=0)
qml.PhaseShift(0.542, wires=0)
expval(qml.PauliZ(0))
with pytest.raises(
ValueError,
match="The PhaseShift gate is not currently supported"):
tape.jacobian(dev)
def test_pauli_rotation_gradient(self, G, theta, tol):
"""Tests that the automatic gradients of Pauli rotations are correct."""
dev = qml.device("default.qubit", wires=1)
with ReversibleTape() as tape:
qml.QubitStateVector(np.array([1.0, -1.0]) / np.sqrt(2), wires=0)
G(theta, wires=[0])
expval(qml.PauliZ(0))
tape.trainable_params = {1}
autograd_val = tape.jacobian(dev, method="analytic")
# compare to finite differences
numeric_val = tape.jacobian(dev, method="numeric")
assert np.allclose(autograd_val, numeric_val, atol=tol, rtol=0)
def test_Rot_gradient(self, theta, tol):
"""Tests that the automatic gradient of a arbitrary Euler-angle-parameterized gate is correct."""
dev = qml.device("default.qubit", wires=1)
params = np.array([theta, theta**3, np.sqrt(2) * theta])
with ReversibleTape() as tape:
qml.QubitStateVector(np.array([1.0, -1.0]) / np.sqrt(2), wires=0)
qml.Rot(*params, wires=[0])
expval(qml.PauliZ(0))
tape.trainable_params = {1, 2, 3}
autograd_val = tape.jacobian(dev, method="analytic")
# compare to finite differences
numeric_val = tape.jacobian(dev, method="numeric")
assert np.allclose(autograd_val, numeric_val, atol=tol, rtol=0)
def test_gradients(self, op, obs, mocker, tol):
"""Tests that the gradients of circuits match between the
finite difference and analytic methods."""
args = np.linspace(0.2, 0.5, op.num_params)
with ReversibleTape() as tape:
qml.Hadamard(wires=0)
qml.RX(0.543, wires=0)
qml.CNOT(wires=[0, 1])
op(*args, wires=range(op.num_wires))
qml.Rot(1.3, -2.3, 0.5, wires=[0])
qml.RZ(-0.5, wires=0)
qml.RY(0.5, wires=1)
qml.CNOT(wires=[0, 1])
expval(obs(wires=0))
expval(qml.PauliZ(wires=1))
dev = qml.device("default.qubit", wires=2)
res = tape.execute(dev)
tape._update_gradient_info()
tape.trainable_params = set(range(1, 1 + op.num_params))
# check that every parameter is analytic
for i in range(op.num_params):
assert tape._par_info[1 + i]["grad_method"][0] == "A"
grad_F = tape.jacobian(dev, method="numeric")
spy = mocker.spy(ReversibleTape, "analytic_pd")
spy_execute = mocker.spy(tape, "execute_device")
grad_A = tape.jacobian(dev, method="analytic")
spy.assert_called()
# check that the execute device method has only been called
# once, for all parameters.
spy_execute.assert_called_once()
assert np.allclose(grad_A, grad_F, atol=tol, rtol=0)
def test_rx_gradient(self, tol):
"""Test that the gradient of the RX gate matches the known formula."""
dev = qml.device("default.qubit", wires=2)
a = 0.7418
with ReversibleTape() as tape:
qml.RX(a, wires=0)
expval(qml.PauliZ(0))
circuit_output = tape.execute(dev)
expected_output = np.cos(a)
assert np.allclose(circuit_output, expected_output, atol=tol, rtol=0)
# circuit jacobians
circuit_jacobian = tape.jacobian(dev, method="analytic")
expected_jacobian = -np.sin(a)
assert np.allclose(circuit_jacobian,
expected_jacobian,
atol=tol,
rtol=0)
def test_gradient_gate_with_multiple_parameters(self, tol):
"""Tests that gates with multiple free parameters yield correct gradients."""
x, y, z = [0.5, 0.3, -0.7]
with ReversibleTape() as tape:
qml.RX(0.4, wires=[0])
qml.Rot(x, y, z, wires=[0])
qml.RY(-0.2, wires=[0])
expval(qml.PauliZ(0))
tape.trainable_params = {1, 2, 3}
dev = qml.device("default.qubit", wires=1)
grad_A = tape.jacobian(dev, method="analytic")
grad_F = tape.jacobian(dev, method="numeric")
# gradient has the correct shape and every element is nonzero
assert grad_A.shape == (1, 3)
assert np.count_nonzero(grad_A) == 3
# the different methods agree
assert np.allclose(grad_A, grad_F, atol=tol, rtol=0)
def test_matrix_elem(self, wires, vec1, obs, vec2, expected):
"""Tests for the helper function _matrix_elem"""
dev = qml.device("default.qubit", wires=wires)
tape = ReversibleTape()
res = tape._matrix_elem(vec1, obs, vec2, dev)
assert res == expected