82 lines
6.2 KiB
Plaintext
82 lines
6.2 KiB
Plaintext
---
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title: Hessian
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description: API reference for qiskit.opflow.gradients.Hessian
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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.gradients.Hessian
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---
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# Hessian
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<Class id="qiskit.opflow.gradients.Hessian" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.46/qiskit/opflow/gradients/hessian.py" signature="qiskit.opflow.gradients.Hessian(hess_method='param_shift', **kwargs)" modifiers="class">
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Bases: [`HessianBase`](qiskit.opflow.gradients.HessianBase "qiskit.opflow.gradients.hessian_base.HessianBase")
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Deprecated: Compute the Hessian of an expected value.
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<Admonition title="Deprecated since version 0.24.0" type="danger">
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The class `qiskit.opflow.gradients.hessian.Hessian` 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](https://qisk.it/opflow_migration).
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</Admonition>
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## Attributes
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### hess\_method
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<Attribute id="qiskit.opflow.gradients.Hessian.hess_method">
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Returns `CircuitGradient`.
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**Returns**
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`CircuitGradient`.
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</Attribute>
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## Methods
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### convert
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<Function id="qiskit.opflow.gradients.Hessian.convert" signature="convert(operator, params=None)">
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**Parameters**
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* **operator** ([*OperatorBase*](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")) – The operator for which we compute the Hessian
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* **params** ([*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*,* [*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*] |* [*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*,* [*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*]] |* [*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*] |* [*ParameterVector*](qiskit.circuit.ParameterVector "qiskit.circuit.parametervector.ParameterVector") *| None*) – The parameters we are computing the Hessian with respect to Either give directly the tuples/list of tuples for which the second order derivative is to be computed or give a list of parameters to build the full Hessian for those parameters. If not explicitly passed, the full Hessian is constructed. The parameters are then inferred from the operator and sorted by name.
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**Returns**
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An operator whose evaluation yields the Hessian
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**Return type**
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[OperatorBase](qiskit.opflow.OperatorBase "qiskit.opflow.OperatorBase")
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</Function>
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### get\_hessian
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<Function id="qiskit.opflow.gradients.Hessian.get_hessian" signature="get_hessian(operator, params=None)">
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Get the Hessian for the given operator w\.r.t. the given parameters
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**Parameters**
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* **operator** ([*OperatorBase*](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")) – Operator w\.r.t. which we take the Hessian.
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* **params** ([*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*,* [*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*] |* [*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*Tuple*](https://docs.python.org/3/library/typing.html#typing.Tuple "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*,* [*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*]] |* [*List*](https://docs.python.org/3/library/typing.html#typing.List "(in Python v3.12)")*\[*[*ParameterExpression*](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")*] |* [*ParameterVector*](qiskit.circuit.ParameterVector "qiskit.circuit.parametervector.ParameterVector") *| None*) – Parameters w\.r.t. which we compute the Hessian. If not explicitly passed, the full Hessian is constructed. The parameters are then inferred from the operator and sorted by name.
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**Returns**
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Operator which represents the gradient w\.r.t. the given params.
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**Raises**
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* [**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – If `params` contains a parameter not present in `operator`.
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* [**ValueError**](https://docs.python.org/3/library/exceptions.html#ValueError "(in Python v3.12)") – If `operator` is not parameterized.
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* [**OpflowError**](opflow#qiskit.opflow.OpflowError "qiskit.opflow.OpflowError") – If the coefficient of the operator could not be reduced to 1.
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* [**OpflowError**](opflow#qiskit.opflow.OpflowError "qiskit.opflow.OpflowError") – If the differentiation of a combo\_fn requires JAX but the package is not installed.
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* [**TypeError**](https://docs.python.org/3/library/exceptions.html#TypeError "(in Python v3.12)") – If the operator does not include a StateFn given by a quantum circuit
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* [**TypeError**](https://docs.python.org/3/library/exceptions.html#TypeError "(in Python v3.12)") – If the parameters were given in an unsupported format.
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* [**Exception**](https://docs.python.org/3/library/exceptions.html#Exception "(in Python v3.12)") – Unintended code is reached
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* [**MissingOptionalLibraryError**](exceptions#qiskit.exceptions.MissingOptionalLibraryError "qiskit.exceptions.MissingOptionalLibraryError") – jax not installed
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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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