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

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.

Deprecated since version 0.24.0: 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:

ExpectationBase