def test_step_and_cost_with_grad_fn_grouped_input(self, tol):
"""Test that the correct cost and update is returned via the step_and_cost
method for the QNG optimizer when providing an explicit grad_fn.
Using a circuit with a single input containing all parameters."""
dev = qml.device("default.qubit", wires=1)
@qml.qnode(dev)
def circuit(params):
qml.RX(params[0], wires=0)
qml.RY(params[1], wires=0)
return qml.expval(qml.PauliZ(0))
var = np.array([0.011, 0.012])
opt = qml.QNGOptimizer(stepsize=0.01)
# With autograd gradient function
grad_fn = qml.grad(circuit)
step1, cost1 = opt.step_and_cost(circuit, var, grad_fn=grad_fn)
step2 = opt.step(circuit, var, grad_fn=grad_fn)
# With more custom gradient function, forward has to be computed explicitly.
grad_fn = lambda param: np.array(qml.grad(circuit)(param))
step3, cost2 = opt.step_and_cost(circuit, var, grad_fn=grad_fn)
step4 = opt.step(circuit, var, grad_fn=grad_fn)
expected_step = var - opt.stepsize * 4 * grad_fn(var)
expected_cost = circuit(var)
for step in [step1, step2, step3, step3]:
assert np.allclose(step, expected_step)
assert np.isclose(cost1, expected_cost)
assert np.isclose(cost2, expected_cost)
def test_var_two_wires_with_parameters(self, qubit_device_2_wires, tol, name, input, expected_output, par):
"""Tests that variances are properly calculated for two-wire observables with parameters."""
qubit_device_2_wires._state = np.array(input)
res = qubit_device_2_wires.var(name, wires=[0, 1], par=par)
assert np.isclose(res, expected_output, atol=tol, rtol=0)
def test_four_term_case(self):
"""Tests the parameter shift rules for `CommutingEvolution` equal the
finite difference result for a four term shift rule case."""
n_wires = 2
dev = qml.device("default.qubit", wires=n_wires)
coeffs = [1, -1]
obs = [qml.PauliX(0) @ qml.PauliY(1), qml.PauliY(0) @ qml.PauliX(1)]
hamiltonian = qml.Hamiltonian(coeffs, obs)
frequencies = (2, 4)
@qml.qnode(dev)
def circuit(time):
qml.PauliX(0)
qml.CommutingEvolution(hamiltonian, time, frequencies)
return qml.expval(qml.PauliZ(0))
x_vals = [
np.array(x, requires_grad=True)
for x in np.linspace(-np.pi, np.pi, num=10)
]
grads_finite_diff = [
qml.gradients.finite_diff(circuit)(x) for x in x_vals
]
grads_param_shift = [
qml.gradients.param_shift(circuit)(x) for x in x_vals
]
assert all(np.isclose(grads_finite_diff, grads_param_shift, atol=1e-4))
def test_two_term_case(self):
"""Tests the parameter shift rules for `CommutingEvolution` equal the
finite difference result for a two term shift rule case."""
n_wires = 1
dev = qml.device("default.qubit", wires=n_wires)
hamiltonian = qml.Hamiltonian([1], [qml.PauliX(0)])
frequencies = (2, )
@qml.qnode(dev)
def circuit(time):
qml.PauliX(0)
qml.CommutingEvolution(hamiltonian, time, frequencies)
return qml.expval(qml.PauliZ(0))
x_vals = np.linspace(-np.pi, np.pi, num=10)
grads_finite_diff = [
qml.gradients.finite_diff(circuit)(x) for x in x_vals
]
grads_param_shift = [
qml.gradients.param_shift(circuit)(x) for x in x_vals
]
assert all(np.isclose(grads_finite_diff, grads_param_shift, atol=1e-4))
def test_adjoint():
"""Tests the CommutingEvolution.adjoint method provides the correct adjoint operation."""
n_wires = 2
dev1 = qml.device("default.qubit", wires=n_wires)
dev2 = qml.device("default.qubit", wires=n_wires)
obs = [qml.PauliX(0) @ qml.PauliY(1), qml.PauliY(0) @ qml.PauliX(1)]
coeffs = [1, -1]
hamiltonian = qml.Hamiltonian(coeffs, obs)
frequencies = (2, )
@qml.qnode(dev1)
def adjoint_evolution_circuit(time):
for i in range(n_wires):
qml.Hadamard(i)
qml.adjoint(qml.CommutingEvolution)(hamiltonian, time, frequencies)
return qml.expval(qml.PauliZ(1))
@qml.qnode(dev2)
def evolution_circuit(time):
for i in range(n_wires):
qml.Hadamard(i)
qml.CommutingEvolution(hamiltonian, time, frequencies)
return qml.expval(qml.PauliZ(1))
evolution_circuit(0.13)
adjoint_evolution_circuit(-0.13)
assert all(np.isclose(dev1.state, dev2.state))
def test_differentiable_hamiltonian(self):
"""Tests correct gradients are produced when the Hamiltonian is differentiable."""
n_wires = 2
dev = qml.device("default.qubit", wires=n_wires)
obs = [qml.PauliX(0) @ qml.PauliY(1), qml.PauliY(0) @ qml.PauliX(1)]
diff_coeffs = np.array([1.0, -1.0], requires_grad=True)
frequencies = (2, 4)
def parameterized_hamiltonian(coeffs):
return qml.Hamiltonian(coeffs, obs)
@qml.qnode(dev)
def circuit(time, coeffs):
qml.PauliX(0)
qml.CommutingEvolution(parameterized_hamiltonian(coeffs), time,
frequencies)
return qml.expval(qml.PauliZ(0))
x_vals = [
np.array(x, requires_grad=True)
for x in np.linspace(-np.pi, np.pi, num=10)
]
grads_finite_diff = [
np.hstack(qml.gradients.finite_diff(circuit)(x, diff_coeffs))
for x in x_vals
]
grads_param_shift = [
np.hstack(qml.gradients.param_shift(circuit)(x, diff_coeffs))
for x in x_vals
]
assert np.isclose(grads_finite_diff, grads_param_shift,
atol=1e-6).all()
def test_single_step(self, qnode, param, nums_frequency, spectra,
substep_optimizer, substep_kwargs):
"""Test executing a single step of the RotosolveOptimizer on a QNode."""
param = tuple(np.array(p, requires_grad=True) for p in param)
opt = RotosolveOptimizer(substep_optimizer, substep_kwargs)
repack_param = len(param) == 1
new_param_step = opt.step(
qnode,
*param,
nums_frequency=nums_frequency,
spectra=spectra,
)
if repack_param:
new_param_step = (new_param_step, )
assert (np.isscalar(new_param_step)
and np.isscalar(param)) or len(new_param_step) == len(param)
new_param_step_and_cost, old_cost = opt.step_and_cost(
qnode,
*param,
nums_frequency=nums_frequency,
spectra=spectra,
)
if repack_param:
new_param_step_and_cost = (new_param_step_and_cost, )
assert np.allclose(
np.fromiter(_flatten(new_param_step_and_cost), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
)
assert np.isclose(qnode(*param), old_cost)
def test_full_output(self, fun, x_min, param, num_freq, optimizer, optimizer_kwargs):
"""Tests the ``full_output`` feature of Rotosolve, delivering intermediate cost
function values at the univariate optimization substeps."""
opt = RotosolveOptimizer()
_, y_output_step = opt.step(
fun,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
full_output=True,
)
new_param, old_cost, y_output_step_and_cost = opt.step_and_cost(
fun,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
full_output=True,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step = (new_param,)
expected_intermediate_x = successive_params(param, new_param)
expected_y_output = [fun(*par) for par in expected_intermediate_x[1:]]
assert np.allclose(y_output_step, expected_y_output)
assert np.allclose(y_output_step_and_cost, expected_y_output)
assert np.isclose(old_cost, fun(*expected_intermediate_x[0]))
def test_single_step(self, qnode, param, num_freq, optimizer, optimizer_kwargs):
opt = RotosolveOptimizer()
repack_param = len(param) == 1
new_param_step = opt.step(
qnode,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
)
if repack_param:
new_param_step = (new_param_step,)
assert (np.isscalar(new_param_step) and np.isscalar(param)) or len(new_param_step) == len(
param
)
new_param_step_and_cost, old_cost = opt.step_and_cost(
qnode,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
)
if repack_param:
new_param_step_and_cost = (new_param_step_and_cost,)
assert np.allclose(
np.fromiter(_flatten(new_param_step_and_cost), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
)
assert np.isclose(qnode(*param), old_cost)
def test_var_single_wire_with_parameters(self, qubit_device_1_wire, tol, name, input, expected_output, par):
"""Tests that expectation values are properly calculated for single-wire observables with parameters."""
qubit_device_1_wire._state = np.array(input)
res = qubit_device_1_wire.var(name, wires=[0], par=par)
assert np.isclose(res, expected_output, atol=tol, rtol=0)
def test_single_step_convergence(self, fun, x_min, param, nums_freq,
exp_num_calls, substep_optimizer,
substep_kwargs):
"""Tests convergence for easy classical functions in a single Rotosolve step.
Includes testing of the parameter output shape and the old cost when using step_and_cost."""
opt = RotosolveOptimizer(substep_optimizer, substep_kwargs)
# Make only the first argument trainable
param = (np.array(param[0], requires_grad=True), ) + param[1:]
# Only one argument is marked as trainable -> All other arguments have to stay fixed
new_param_step = opt.step(
fun,
*param,
nums_frequency=nums_freq,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step = (new_param_step, )
assert all(
np.allclose(p, new_p)
for p, new_p in zip(param[1:], new_param_step[1:]))
# With trainable parameters, training should happen
param = tuple(np.array(p, requires_grad=True) for p in param)
new_param_step = opt.step(
fun,
*param,
nums_frequency=nums_freq,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step = (new_param_step, )
assert len(x_min) == len(new_param_step)
assert np.allclose(
np.fromiter(_flatten(x_min), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
# Now with step_and_cost and trainable params
new_param_step_and_cost, old_cost = opt.step_and_cost(
fun,
*param,
nums_frequency=nums_freq,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step_and_cost = (new_param_step_and_cost, )
assert len(x_min) == len(new_param_step_and_cost)
assert np.allclose(
np.fromiter(_flatten(new_param_step_and_cost), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
assert np.isclose(old_cost, fun(*param))
def test_qubit_identity(self, tensornet_device_1_wire, tol):
"""Test that the tensor network plugin provides correct result for the Identity expectation"""
p = 0.543
@qml.qnode(tensornet_device_1_wire)
def circuit(x):
"""Test quantum function"""
qml.RX(x, wires=0)
return qml.expval(qml.Identity(0))
assert np.isclose(circuit(p), 1, atol=tol, rtol=0)
def test_supported_observable_two_wires_with_parameters(self, tensornet_device_2_wires, tol, name, state, expected_output, par):
"""Tests supported observables on two wires with parameters."""
obs = getattr(qml.ops, name)
assert tensornet_device_2_wires.supports_observable(name)
@qml.qnode(tensornet_device_2_wires)
def circuit():
qml.QubitStateVector(np.array(state), wires=[0, 1])
return qml.expval(obs(*par, wires=[0, 1]))
assert np.isclose(circuit(), expected_output, atol=tol, rtol=0)
def test_supported_observable_single_wire_no_parameters(self, tensornet_device_1_wire, tol, name, state, expected_output):
"""Tests supported observables on single wires without parameters."""
obs = getattr(qml.ops, name)
assert tensornet_device_1_wire.supports_observable(name)
@qml.qnode(tensornet_device_1_wire)
def circuit():
qml.QubitStateVector(np.array(state), wires=[0])
return qml.expval(obs(wires=[0]))
assert np.isclose(circuit(), expected_output, atol=tol, rtol=0)
def test_supported_gate_single_wire_with_parameters(self, tensornet_device_1_wire, tol, name, par, expected_output):
"""Tests supported gates that act on a single wire that are parameterized"""
op = getattr(qml.ops, name)
assert tensornet_device_1_wire.supports_operation(name)
@qml.qnode(tensornet_device_1_wire)
def circuit():
op(*par, wires=0)
return qml.expval(qml.PauliZ(0))
assert np.isclose(circuit(), expected_output, atol=tol, rtol=0)
def test_qubit_circuit(self, tensornet_device_1_wire, tol):
"""Test that the tensor network plugin provides correct result for a simple circuit"""
p = 0.543
@qml.qnode(tensornet_device_1_wire)
def circuit(x):
qml.RX(x, wires=0)
return qml.expval(qml.PauliY(0))
expected = -np.sin(p)
assert np.isclose(circuit(p), expected, atol=tol, rtol=0)
def test_random_layer_randomwires(self, n_subsystems):
"""Test that random_layer() picks random wires."""
n_rots = 500
weights = np.random.randn(n_rots)
with qml.utils.OperationRecorder() as rec:
random_layer(weights=weights, wires=range(n_subsystems), ratio_imprim=0.3,
imprimitive=qml.CNOT, rotations=[RX, RY, RZ], seed=42)
wires = [q._wires for q in rec.queue]
wires_flat = [item for w in wires for item in w]
mean_wire = np.mean(wires_flat)
assert np.isclose(mean_wire, (n_subsystems - 1) / 2, atol=0.05)
def test_random_layer_ratio_imprimitive(self, ratio):
"""Test that random_layer() has the right ratio of imprimitive gates."""
n_rots = 500
n_wires = 2
impr = CNOT
weights = np.random.randn(n_rots)
with qml.utils.OperationRecorder() as rec:
random_layer(weights=weights, wires=range(n_wires), ratio_imprim=ratio,
imprimitive=CNOT, rotations=[RX, RY, RZ], seed=42)
types = [type(q) for q in rec.queue]
ratio_impr = types.count(impr) / len(types)
assert np.isclose(ratio_impr, ratio, atol=0.05)
def test_qubit_circuit(self, tol):
"""Test that the device provides the correct
result for a simple circuit."""
p = np.array(0.543)
dev = qml.device("default.qubit.autograd", wires=1)
@qml.qnode(dev, interface="autograd")
def circuit(x):
qml.RX(x, wires=0)
return qml.expval(qml.PauliY(0))
expected = -np.sin(p)
assert circuit.diff_options["method"] == "backprop"
assert np.isclose(circuit(p), expected, atol=tol, rtol=0)
def simplify(self):
r"""Simplifies the Hamiltonian by combining like-terms.
**Example**
>>> ops = [qml.PauliY(2), qml.PauliX(0) @ qml.Identity(1), qml.PauliX(0)]
>>> H = qml.Hamiltonian([1, 1, -2], ops)
>>> H.simplify()
>>> print(H)
(-1) [X0]
+ (1) [Y2]
.. warning::
Calling this method will reset ``grouping_indices`` to None, since
the observables it refers to are updated.
"""
data = []
ops = []
for i in range(len(self.ops)): # pylint: disable=consider-using-enumerate
op = self.ops[i]
c = self.coeffs[i]
op = op if isinstance(op, Tensor) else Tensor(op)
ind = None
for j, o in enumerate(ops):
if op.compare(o):
ind = j
break
if ind is not None:
data[ind] += c
if np.isclose(qml.math.toarray(data[ind]), np.array(0.0)):
del data[ind]
del ops[ind]
else:
ops.append(op.prune())
data.append(c)
self._coeffs = qml.math.stack(data) if data else []
self.data = data
self._ops = ops
# reset grouping, since the indices refer to the old observables and coefficients
self._grouping_indices = None
def test_random_layer_randomwires(self, n_subsystems):
"""Test that pennylane.templates.layers._random_layer() picks random wires."""
np.random.seed(12)
n_rots = 500
dev = qml.device('default.qubit', wires=n_subsystems)
weights = np.random.randn(n_rots)
def circuit(weights):
_random_layer(weights=weights, wires=range(n_subsystems))
return qml.expval(qml.PauliZ(0))
qnode = qml.QNode(circuit, dev)
qnode(weights)
queue = qnode.queue
wires = [q._wires for q in queue]
wires_flat = [item for w in wires for item in w]
mean_wire = np.mean(wires_flat)
assert np.isclose(mean_wire, (n_subsystems - 1) / 2, atol=0.05)
def test_single_step_convergence(
self, fun, x_min, param, num_freq, optimizer, optimizer_kwargs
):
"""Tests convergence for easy classical functions in a single Rotosolve step.
Includes testing of the parameter output shape and the old cost when using step_and_cost."""
opt = RotosolveOptimizer()
new_param_step = opt.step(
fun,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step = (new_param_step,)
assert len(x_min) == len(new_param_step)
assert np.allclose(
np.fromiter(_flatten(x_min), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
new_param_step_and_cost, old_cost = opt.step_and_cost(
fun,
*param,
num_freqs=num_freq,
optimizer=optimizer,
optimizer_kwargs=optimizer_kwargs,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step_and_cost = (new_param_step_and_cost,)
assert len(x_min) == len(new_param_step_and_cost)
assert np.allclose(
np.fromiter(_flatten(new_param_step_and_cost), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
assert np.isclose(old_cost, fun(*param))
def test_random_layer_imprimitive(self, ratio):
"""Test that pennylane.templates.layers.RandomLayer() has the right ratio of imprimitive gates."""
np.random.seed(12)
n_rots = 500
n_wires = 2
impr = CNOT
dev = qml.device('default.qubit', wires=n_wires)
weights = np.random.randn(n_rots)
def circuit(weights):
RandomLayer(weights=weights, wires=range(n_wires), ratio_imprim=ratio, impr=CNOT)
return qml.expval(qml.PauliZ(0))
qnode = qml.QNode(circuit, dev)
qnode(weights)
queue = qnode.queue
types = [type(q) for q in queue]
ratio_impr = types.count(impr) / len(types)
assert np.isclose(ratio_impr, ratio, atol=0.05)
def test_nonzero_shots(self, tol):
"""Test that the default qubit plugin provides correct result for high shot number"""
shots = 10 ** 5
dev = qml.device("default.qubit", wires=1, shots=shots)
p = 0.543
@qml.qnode(dev)
def circuit(x):
"""Test quantum function"""
qml.RX(x, wires=0)
return qml.expval(qml.PauliY(0))
runs = []
for _ in range(100):
runs.append(circuit(p))
assert np.isclose(np.mean(runs), -np.sin(p), atol=tol, rtol=0)
def test_state_preparation_fidelity(self, tol, qubit_device_3_wires,
state_vector, wires, target_state):
"""Tests that the template MottonenStatePreparation integrates correctly with PennyLane
and produces states with correct fidelity."""
@qml.qnode(qubit_device_3_wires)
def circuit():
MottonenStatePreparation(state_vector, wires)
return qml.expval(qml.PauliZ(0)), qml.expval(
qml.PauliZ(1)), qml.expval(qml.PauliZ(2))
circuit()
state = circuit.device.state.ravel()
fidelity = abs(np.vdot(state, target_state))**2
# We test for fidelity here, because the vector themselves will hardly match
# due to imperfect state preparation
assert np.isclose(fidelity, 1, atol=tol, rtol=0)
def test_multi_qub_readout_correction(self):
"""Test the QPU plugin with readout errors and correction"""
device = np.random.choice(TEST_QPU_LATTICES)
dev_qpu = qml.device("forest.qpu",
device=device,
load_qc=False,
shots=10_000,
readout_error=[0.9, 0.75],
symmetrize_readout='exhaustive',
calibrate_readout='plus-eig',
parametric_compilation=False)
@qml.qnode(dev_qpu)
def circuit():
qml.RY(np.pi / 2, wires=0)
qml.RY(np.pi / 3, wires=1)
return qml.expval(qml.PauliX(0) @ qml.PauliZ(1))
result = circuit()
assert np.isclose(result, 0.5, atol=3e-2)
def test_single_step(self, fun, x_min, param, num_freq):
"""Tests convergence for easy classical functions in a single Rotosolve step
with some arguments deactivated for training.
Includes testing of the parameter output shape and the old cost when using step_and_cost."""
substep_optimizer = "brute"
substep_kwargs = None
opt = RotosolveOptimizer(substep_optimizer, substep_kwargs)
new_param_step = opt.step(
fun,
*param,
nums_frequency=num_freq,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step = (new_param_step, )
assert len(x_min) == len(new_param_step)
assert np.allclose(
np.fromiter(_flatten(x_min), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
new_param_step_and_cost, old_cost = opt.step_and_cost(
fun,
*param,
nums_frequency=num_freq,
)
# The following accounts for the unpacking functionality for length-1 param
if len(param) == 1:
new_param_step_and_cost = (new_param_step_and_cost, )
assert len(x_min) == len(new_param_step_and_cost)
assert np.allclose(
np.fromiter(_flatten(new_param_step_and_cost), dtype=float),
np.fromiter(_flatten(new_param_step), dtype=float),
atol=1e-5,
)
assert np.isclose(old_cost, fun(*param))
def test_random_layer_randomwires(self, n_subsystems):
"""Test that _random_layer() picks random wires."""
n_rots = 500
dev = qml.device('default.qubit', wires=n_subsystems)
weights = np.random.randn(n_rots)
def circuit(weights):
_random_layer(weights=weights,
wires=range(n_subsystems),
ratio_imprim=0.3,
imprimitive=qml.CNOT,
rotations=[RX, RY, RZ],
seed=42)
return qml.expval(qml.PauliZ(0))
qnode = qml.QNode(circuit, dev)
qnode(weights)
queue = qnode.queue
wires = [q._wires for q in queue]
wires_flat = [item for w in wires for item in w]
mean_wire = np.mean(wires_flat)
assert np.isclose(mean_wire, (n_subsystems - 1) / 2, atol=0.05)
def test_multi_qub_no_readout_errors(self):
"""Test the QPU plugin with no readout errors or correction"""
device = np.random.choice(TEST_QPU_LATTICES)
dev_qpu = qml.device(
"forest.qpu",
device=device,
load_qc=False,
symmetrize_readout=None,
calibrate_readout=None,
)
@qml.qnode(dev_qpu)
def circuit():
qml.RY(np.pi / 2, wires=0)
qml.RY(np.pi / 3, wires=1)
return qml.expval(qml.PauliX(0) @ qml.PauliZ(1))
num_expts = 50
result = 0.0
for _ in range(num_expts):
result += circuit()
result /= num_expts
assert np.isclose(result, 0.5, atol=2e-2)
def __init__(
self,
ansatz,
hamiltonian,
device,
interface="autograd",
diff_method="best",
optimize=False,
**kwargs,
):
if kwargs.get("measure", "expval") != "expval":
raise ValueError(
"ExpvalCost can only be used to construct sums of expectation values."
)
coeffs, observables = hamiltonian.terms
self.hamiltonian = hamiltonian
"""Hamiltonian: the input Hamiltonian."""
self.qnodes = None
"""QNodeCollection: The QNodes to be evaluated. Each QNode corresponds to the expectation
value of each observable term after applying the circuit ansatz."""
self._multiple_devices = isinstance(device, Sequence)
"""Bool: Records if multiple devices are input"""
if np.isclose(qml.math.toarray(qml.math.count_nonzero(coeffs)), 0):
self.cost_fn = lambda *args, **kwargs: np.array(0)
return
self._optimize = optimize
self.qnodes = qml.map(ansatz,
observables,
device,
interface=interface,
diff_method=diff_method,
**kwargs)
if self._optimize:
if self._multiple_devices:
raise ValueError(
"Using multiple devices is not supported when optimize=True"
)
obs_groupings, coeffs_groupings = qml.grouping.group_observables(
observables, coeffs)
d = device[0] if self._multiple_devices else device
w = d.wires.tolist()
@qml.qnode(device,
interface=interface,
diff_method=diff_method,
**kwargs)
def circuit(*qnode_args, obs, **qnode_kwargs):
"""Converting ansatz into a full circuit including measurements"""
ansatz(*qnode_args, wires=w, **qnode_kwargs)
return [qml.expval(o) for o in obs]
def cost_fn(*qnode_args, **qnode_kwargs):
"""Combine results from grouped QNode executions with grouped coefficients"""
if device.shot_vector:
shots_batch = 0
for i in device.shot_vector:
shots_batch += i[1]
total = [0] * shots_batch
for o, c in zip(obs_groupings, coeffs_groupings):
res = circuit(*qnode_args, obs=o, **qnode_kwargs)
for i, batch_res in enumerate(res):
total[i] += sum(batch_res * c)
else:
total = 0
for o, c in zip(obs_groupings, coeffs_groupings):
res = circuit(*qnode_args, obs=o, **qnode_kwargs)
total += sum([r * c_ for r, c_ in zip(res, c)])
return total
self.cost_fn = cost_fn
else:
self.cost_fn = qml.dot(coeffs, self.qnodes)