def sparse(
self,
qubits: Optional[Sequence['cirq.Qid']] = None
) -> 'cirq.PauliString':
"""A `cirq.PauliString` version of this dense pauli string.
Args:
qubits: The qubits to apply the Paulis to. Defaults to
`cirq.LineQubit.range(len(self))`.
Returns:
A `cirq.PauliString` with the non-identity operations from
this dense pauli string applied to appropriate qubits.
Raises:
ValueError: If the number of qubits supplied does not match that of
this instance.
"""
if qubits is None:
from cirq import devices
qubits = devices.LineQubit.range(len(self))
if len(qubits) != len(self):
raise ValueError('Wrong number of qubits.')
return pauli_string.PauliString(
coefficient=self.coefficient,
qubit_pauli_map={
q: PAULI_GATES[p]
for q, p in zip(qubits, self.pauli_mask) if p
},
)
def approx_pauli_string_expectation(
observable: 'cirq.PAULI_STRING_LIKE',
num_samples: int,
key: Hashable = '') -> ApproxPauliStringExpectation:
return ApproxPauliStringExpectation(pauli_string.PauliString(observable),
num_samples,
key=key)
