63 lines
3.1 KiB
Plaintext
63 lines
3.1 KiB
Plaintext
---
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title: PauliExpectation
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description: API reference for qiskit.opflow.expectations.PauliExpectation
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in_page_toc_min_heading_level: 1
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python_api_type: class
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python_api_name: qiskit.opflow.expectations.PauliExpectation
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---
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# PauliExpectation
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<Class id="qiskit.opflow.expectations.PauliExpectation" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.25/qiskit/opflow/expectations/pauli_expectation.py" signature="qiskit.opflow.expectations.PauliExpectation(group_paulis=True)" modifiers="class">
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Bases: [`ExpectationBase`](qiskit.opflow.expectations.ExpectationBase "qiskit.opflow.expectations.expectation_base.ExpectationBase")
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An Expectation converter for Pauli-basis observables by changing Pauli measurements to a diagonal (\{Z, I}^n) basis and appending circuit post-rotations to the measured state function. Optionally groups the Paulis with the same post-rotations (those that commute with one another, or form Abelian groups) into single measurements to reduce circuit execution overhead.
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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The class `qiskit.opflow.expectations.pauli_expectation.PauliExpectation` 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](https://qisk.it/opflow_migration).
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</Admonition>
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**Parameters**
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**group\_paulis** ([*bool*](https://docs.python.org/3/library/functions.html#bool "(in Python v3.12)")) – Whether to group the Pauli measurements into commuting sums, which all have the same diagonalizing circuit.
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## Methods
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### compute\_variance
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<Function id="qiskit.opflow.expectations.PauliExpectation.compute_variance" signature="compute_variance(exp_op)">
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Compute the variance of the expectation estimator.
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**Parameters**
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**exp\_op** ([*OperatorBase*](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")) – The full expectation value Operator after sampling.
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**Returns**
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The variances or lists thereof (if exp\_op contains ListOps) of the expectation value estimation.
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**Return type**
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[list](https://docs.python.org/3/library/stdtypes.html#list "(in Python v3.12)") | [float](https://docs.python.org/3/library/functions.html#float "(in Python v3.12)") | [*ndarray*](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.html#numpy.ndarray "(in NumPy v1.26)")
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</Function>
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### convert
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<Function id="qiskit.opflow.expectations.PauliExpectation.convert" signature="convert(operator)">
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Accepts an Operator and returns a new Operator with the Pauli measurements replaced by diagonal Pauli post-rotation based measurements so they can be evaluated by sampling and averaging.
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**Parameters**
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**operator** ([*OperatorBase*](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")) – The operator to convert.
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**Returns**
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The converted operator.
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**Return type**
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[*OperatorBase*](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")
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</Function>
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</Class>
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