def to_torch(self, dtype=None):
"""Apply the Torch interface to the internal quantum tape.
Args:
dtype (tf.dtype): The dtype that the Torch QNode should
output. If not provided, the default is ``torch.float64``.
Raises:
qml.QuantumFunctionError: if PyTorch >= 1.3 is not installed
"""
# pylint: disable=import-outside-toplevel
try:
import torch
from pennylane.beta.interfaces.torch import TorchInterface
self.interface = "torch"
if not isinstance(self.dtype, torch.dtype):
self.dtype = None
self.dtype = dtype or self.dtype or TorchInterface.dtype
if self.dtype is np.complex128:
self.dtype = torch.complex128
if self.qtape is not None:
TorchInterface.apply(self.qtape, dtype=self.dtype)
except ImportError:
raise qml.QuantumFunctionError(
"PyTorch not found. Please install the latest "
"version of PyTorch to enable the 'torch' interface.")
def test_complex_min_version(self, monkeypatch):
"""Test if an error is raised when a version of torch before 1.6.0 is used as the dtype
in the apply() method"""
with monkeypatch.context() as m:
m.setattr(qml.beta.interfaces.torch, "COMPLEX_SUPPORT", False)
with pytest.raises(qml.QuantumFunctionError,
match="Version 1.6.0 or above of PyTorch"):
TorchInterface.apply(QuantumTape(), dtype=torch.complex128)
def test_repeated_interface_construction(self):
"""Test that the interface is correctly applied multiple times"""
with TorchInterface.apply(QuantumTape()) as tape:
qml.RX(0.5, wires=0)
expval(qml.PauliX(0))
assert tape.interface == "torch"
assert isinstance(tape, TorchInterface)
assert tape.__bare__ == QuantumTape
TorchInterface.apply(tape, dtype=torch.float32)
assert tape.interface == "torch"
assert isinstance(tape, TorchInterface)
assert tape.__bare__ == QuantumTape
assert tape.dtype is torch.float32
def test_ragged_differentiation(self, tol):
"""Tests correct output shape and evaluation for a tape
with prob and expval outputs"""
dev = qml.device("default.qubit", wires=2)
x_val = 0.543
y_val = -0.654
x = torch.tensor(x_val, requires_grad=True)
y = torch.tensor(y_val, requires_grad=True)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RX(x, wires=[0])
qml.RY(y, wires=[1])
qml.CNOT(wires=[0, 1])
expval(qml.PauliZ(0))
probs(wires=[1])
res = tape.execute(dev)
expected = np.array([
np.cos(x_val),
(1 + np.cos(x_val) * np.cos(y_val)) / 2,
(1 - np.cos(x_val) * np.cos(y_val)) / 2,
])
assert np.allclose(res.detach().numpy(), expected, atol=tol, rtol=0)
loss = torch.sum(res)
loss.backward()
expected = np.array([
-np.sin(x_val) + -np.sin(x_val) * np.cos(y_val) / 2 +
np.cos(y_val) * np.sin(x_val) / 2,
-np.cos(x_val) * np.sin(y_val) / 2 +
np.cos(x_val) * np.sin(y_val) / 2,
])
assert np.allclose(x.grad, expected[0], atol=tol, rtol=0)
assert np.allclose(y.grad, expected[1], atol=tol, rtol=0)
def test_classical_processing(self, tol):
"""Test classical processing within the quantum tape"""
p_val = [0.1, 0.2]
params = torch.tensor(p_val, requires_grad=True)
dev = qml.device("default.qubit", wires=1)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RY(params[0] * params[1], wires=0)
qml.RZ(0.2, wires=0)
qml.RX(params[1] + params[1]**2 + torch.sin(params[0]), wires=0)
expval(qml.PauliZ(0))
assert tape.trainable_params == {0, 2}
tape_params = [i.detach().numpy() for i in tape.get_parameters()]
assert np.allclose(
tape_params,
[p_val[0] * p_val[1], p_val[1] + p_val[1]**2 + np.sin(p_val[0])],
atol=tol,
rtol=0,
)
res = tape.execute(dev)
res.backward()
assert isinstance(params.grad, torch.Tensor)
assert params.shape == (2, )
def test_jacobian_dtype(self, tol):
"""Test calculating the jacobian with a different datatype"""
a_val = 0.1
b_val = 0.2
a = torch.tensor(a_val, requires_grad=True, dtype=torch.float32)
b = torch.tensor(b_val, requires_grad=True, dtype=torch.float32)
dev = qml.device("default.qubit", wires=2)
with TorchInterface.apply(QuantumTape(), dtype=torch.float32) as tape:
qml.RY(a, wires=0)
qml.RX(b, wires=1)
qml.CNOT(wires=[0, 1])
expval(qml.PauliZ(0))
expval(qml.PauliY(1))
assert tape.trainable_params == {0, 1}
res = tape.execute(dev)
assert isinstance(res, torch.Tensor)
assert res.shape == (2, )
assert res.dtype is torch.float32
loss = torch.sum(res)
loss.backward()
assert a.grad.dtype is torch.float32
assert b.grad.dtype is torch.float32
def test_interface_construction(self):
"""Test that the interface is correctly applied"""
with TorchInterface.apply(QuantumTape()) as tape:
qml.RX(0.5, wires=0)
expval(qml.PauliX(0))
assert tape.interface == "torch"
assert isinstance(tape, TorchInterface)
assert tape.__bare__ == QuantumTape
def test_sampling(self):
"""Test sampling works as expected"""
dev = qml.device("default.qubit", wires=2, shots=10)
with TorchInterface.apply(QuantumTape()) as tape:
qml.Hadamard(wires=[0])
qml.CNOT(wires=[0, 1])
sample(qml.PauliZ(0))
sample(qml.PauliX(1))
res = tape.execute(dev)
assert res.shape == (2, 10)
assert isinstance(res, torch.Tensor)
def test_execution(self):
"""Test execution"""
a = torch.tensor(0.1, requires_grad=True)
dev = qml.device("default.qubit", wires=1)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RY(a, wires=0)
qml.RX(torch.tensor(0.2), wires=0)
expval(qml.PauliZ(0))
assert tape.trainable_params == {0}
res = tape.execute(dev)
assert isinstance(res, torch.Tensor)
assert res.shape == (1, )
def test_get_parameters(self):
"""Test that the get parameters function correctly sets and returns the
trainable parameters"""
a = torch.tensor(0.1, requires_grad=True)
b = torch.tensor(0.2)
c = torch.tensor(0.3, requires_grad=True)
d = 0.4
with TorchInterface.apply(QuantumTape()) as tape:
qml.Rot(a, b, c, wires=0)
qml.RX(d, wires=1)
qml.CNOT(wires=[0, 1])
expval(qml.PauliX(0))
assert tape.trainable_params == {0, 2}
assert np.all(tape.get_parameters() == [a, c])
def test_jacobian_options(self, mocker, tol):
"""Test setting jacobian options"""
spy = mocker.spy(QuantumTape, "numeric_pd")
a = torch.tensor([0.1, 0.2], requires_grad=True)
dev = qml.device("default.qubit", wires=1)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RY(a[0], wires=0)
qml.RX(a[1], wires=0)
expval(qml.PauliZ(0))
tape.jacobian_options = {"h": 1e-8, "order": 2}
res = tape.execute(dev)
res.backward()
for args in spy.call_args_list:
assert args[1]["order"] == 2
assert args[1]["h"] == 1e-8
def test_jacobian(self, mocker, tol):
"""Test jacobian calculation"""
spy = mocker.spy(QuantumTape, "jacobian")
a_val = 0.1
b_val = 0.2
a = torch.tensor(a_val, requires_grad=True)
b = torch.tensor(b_val, requires_grad=True)
dev = qml.device("default.qubit", wires=2)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RZ(torch.tensor(0.543), wires=0)
qml.RY(a, wires=0)
qml.RX(b, wires=1)
qml.CNOT(wires=[0, 1])
expval(qml.PauliZ(0))
expval(qml.PauliY(1))
assert tape.trainable_params == {1, 2}
res = tape.execute(dev)
assert isinstance(res, torch.Tensor)
assert res.shape == (2, )
expected = [np.cos(a_val), -np.cos(a_val) * np.sin(b_val)]
assert np.allclose(res.detach().numpy(), expected, atol=tol, rtol=0)
loss = torch.sum(res)
loss.backward()
expected = [
-np.sin(a_val) + np.sin(a_val) * np.sin(b_val),
-np.cos(a_val) * np.cos(b_val)
]
assert np.allclose(a.grad, expected[0], atol=tol, rtol=0)
assert np.allclose(b.grad, expected[1], atol=tol, rtol=0)
spy.assert_called()
def test_reusing_quantum_tape(self, tol):
"""Test re-using a quantum tape by passing new parameters"""
a = torch.tensor(0.1, requires_grad=True)
b = torch.tensor(0.2, requires_grad=True)
dev = qml.device("default.qubit", wires=2)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RY(a, wires=0)
qml.RX(b, wires=1)
qml.CNOT(wires=[0, 1])
expval(qml.PauliZ(0))
expval(qml.PauliY(1))
assert tape.trainable_params == {0, 1}
loss = torch.sum(tape.execute(dev))
loss.backward()
a_val = 0.54
b_val = 0.8
a = torch.tensor(a_val, requires_grad=True)
b = torch.tensor(b_val, requires_grad=True)
res2 = tape.execute(dev, params=[2 * a, b])
expected = [np.cos(2 * a_val), -np.cos(2 * a_val) * np.sin(b_val)]
assert np.allclose(res2.detach().numpy(), expected, atol=tol, rtol=0)
loss = torch.sum(res2)
loss.backward()
expected = [
-2 * np.sin(2 * a_val) + 2 * np.sin(2 * a_val) * np.sin(b_val),
-np.cos(2 * a_val) * np.cos(b_val),
]
assert np.allclose(a.grad, expected[0], atol=tol, rtol=0)
assert np.allclose(b.grad, expected[1], atol=tol, rtol=0)
def test_matrix_parameter(self, U, tol):
"""Test that the Torch interface works correctly
with a matrix parameter"""
a_val = 0.1
a = torch.tensor(a_val, requires_grad=True)
dev = qml.device("default.qubit", wires=2)
with TorchInterface.apply(QuantumTape()) as tape:
qml.QubitUnitary(U, wires=0)
qml.RY(a, wires=0)
expval(qml.PauliZ(0))
assert tape.trainable_params == {1}
res = tape.execute(dev)
assert np.allclose(res.detach().numpy(),
-np.cos(a_val),
atol=tol,
rtol=0)
res.backward()
assert np.allclose(a.grad, np.sin(a_val), atol=tol, rtol=0)
def test_no_trainable_parameters(self, tol):
"""Test evaluation and Jacobian if there are no trainable parameters"""
dev = qml.device("default.qubit", wires=2)
with TorchInterface.apply(QuantumTape()) as tape:
qml.RY(0.2, wires=0)
qml.RX(torch.tensor(0.1), wires=0)
qml.CNOT(wires=[0, 1])
expval(qml.PauliZ(0))
expval(qml.PauliZ(1))
assert tape.trainable_params == set()
res = tape.execute(dev)
assert res.shape == (2, )
assert isinstance(res, torch.Tensor)
with pytest.raises(
RuntimeError,
match=
"element 0 of tensors does not require grad and does not have a grad_fn",
):
res.backward()
def test_differentiable_expand(self, mocker, tol):
"""Test that operation and nested tapes expansion
is differentiable"""
mock = mocker.patch.object(qml.operation.Operation, "do_check_domain",
False)
class U3(qml.U3):
def expand(self):
tape = QuantumTape()
theta, phi, lam = self.data
wires = self.wires
tape._ops += [
qml.Rot(lam, theta, -lam, wires=wires),
qml.PhaseShift(phi + lam, wires=wires),
]
return tape
tape = QuantumTape()
dev = qml.device("default.qubit", wires=1)
a = np.array(0.1)
p_val = [0.1, 0.2, 0.3]
p = torch.tensor(p_val, requires_grad=True)
with tape:
qml.RX(a, wires=0)
U3(p[0], p[1], p[2], wires=0)
expval(qml.PauliX(0))
tape = TorchInterface.apply(tape.expand())
assert tape.trainable_params == {1, 2, 3, 4}
assert [i.name for i in tape.operations] == ["RX", "Rot", "PhaseShift"]
tape_params = [i.detach().numpy() for i in tape.get_parameters()]
assert np.allclose(
tape_params, [p_val[2], p_val[0], -p_val[2], p_val[1] + p_val[2]],
atol=tol,
rtol=0)
res = tape.execute(device=dev)
expected = np.cos(a) * np.cos(p_val[1]) * np.sin(p_val[0]) + np.sin(
a) * (np.cos(p_val[2]) * np.sin(p_val[1]) +
np.cos(p_val[0]) * np.cos(p_val[1]) * np.sin(p_val[2]))
assert np.allclose(res.detach().numpy(), expected, atol=tol, rtol=0)
res.backward()
expected = np.array([
np.cos(p_val[1]) *
(np.cos(a) * np.cos(p_val[0]) -
np.sin(a) * np.sin(p_val[0]) * np.sin(p_val[2])),
np.cos(p_val[1]) * np.cos(p_val[2]) * np.sin(a) -
np.sin(p_val[1]) *
(np.cos(a) * np.sin(p_val[0]) +
np.cos(p_val[0]) * np.sin(a) * np.sin(p_val[2])),
np.sin(a) *
(np.cos(p_val[0]) * np.cos(p_val[1]) * np.cos(p_val[2]) -
np.sin(p_val[1]) * np.sin(p_val[2])),
])
assert np.allclose(p.grad, expected, atol=tol, rtol=0)