ExpectationFactory
class qiskit.opflow.expectations.ExpectationFactory
Bases: object
Deprecated: factory class for convenient automatic selection of an Expectation based on the Operator to be converted and backend used to sample the expectation value.
Methods
build
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.
The method qiskit.opflow.expectations.expectation_factory.ExpectationFactory.build() is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. For code migration guidelines, visit https://qisk.it/opflow_migration.
Parameters
- operator (OperatorBase) – The Operator whose expectation value will be taken.
- backend (Backend |QuantumInstance | 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.
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.
Return type