qiskit.aqua.operators.expectations.ExpectationFactory

class ExpectationFactory

A factory class for convenient automatic selection of an Expectation based on the Operator to be converted and backend used to sample the expectation value.

__init__()

Initialize self. See help(type(self)) for accurate signature.

Methods

__init__()	Initialize self.
build(operator[, backend, include_custom])	A factory method for convenient automatic selection of an Expectation based on the Operator to be converted and backend used to sample the expectation value.

static build(operator, backend=None, include_custom=True)

A factory method for convenient automatic selection of an Expectation based on the Operator to be converted and backend used to sample the expectation value.

Parameters

• operator (OperatorBase) – The Operator whose expectation value will be taken.

• backend (Union[QuantumInstance, Backend, BaseBackend, None]) – The backend which will be used to sample the expectation value.

• include_custom (bool) – Whether the factory will include the (Aer) specific custom expectations if their behavior against the backend might not be as expected. For instance when using Aer qasm_simulator with paulis the Aer snapshot can be used but the outcome lacks shot noise and hence does not intuitively behave overall as people might expect when choosing a qasm_simulator. It is however fast as long as the more state vector like behavior is acceptable.

Return type

ExpectationBase

Returns

The expectation algorithm which best fits the Operator and backend.

Raises

ValueError – If operator is not of a composition for which we know the best Expectation method.