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ExpectationFactory

qiskit.opflow.expectations.ExpectationFactory GitHub(opens in a new tab)

Bases: object(opens in a new tab)

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.

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 in the Qiskit 1.0 release. For code migration guidelines, visit https://qisk.it/opflow_migration(opens in a new tab).

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(opens in a new tab)) – 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(opens in a new tab) – If operator is not of a composition for which we know the best Expectation method.

Return type

ExpectationBase

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