155 lines
8.5 KiB
Plaintext
155 lines
8.5 KiB
Plaintext
---
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title: Hessian
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description: API reference for qiskit.aqua.operators.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.aqua.operators.gradients.Hessian
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---
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# qiskit.aqua.operators.gradients.Hessian
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<Class id="qiskit.aqua.operators.gradients.Hessian" isDedicatedPage={true} github="https://github.com/qiskit-community/qiskit-aqua/tree/stable/0.9/qiskit/aqua/operators/gradients/hessian.py" signature="Hessian(hess_method='param_shift', **kwargs)" modifiers="class">
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Compute the Hessian of an expected value.
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**Parameters**
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* **hess\_method** (`Union`\[`str`, `CircuitGradient`]) – The method used to compute the state/probability gradient. Can be either `'param_shift'` or `'lin_comb'` or `'fin_diff'`. Ignored for gradients w\.r.t observable parameters.
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* **kwargs** (*dict*) – Optional parameters for a CircuitGradient
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**Raises**
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**ValueError** – If method != `fin_diff` and `epsilon` is not None.
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### \_\_init\_\_
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<Function id="qiskit.aqua.operators.gradients.Hessian.__init__" signature="__init__(hess_method='param_shift', **kwargs)">
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**Parameters**
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* **hess\_method** (`Union`\[`str`, `CircuitGradient`]) – The method used to compute the state/probability gradient. Can be either `'param_shift'` or `'lin_comb'` or `'fin_diff'`. Ignored for gradients w\.r.t observable parameters.
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* **kwargs** (*dict*) – Optional parameters for a CircuitGradient
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**Raises**
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**ValueError** – If method != `fin_diff` and `epsilon` is not None.
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</Function>
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## Methods
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| | |
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| ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------- |
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| [`__init__`](#qiskit.aqua.operators.gradients.Hessian.__init__ "qiskit.aqua.operators.gradients.Hessian.__init__")(\[hess\_method]) | **type hess\_method**`Union`\[`str`, `CircuitGradient`] |
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| [`convert`](#qiskit.aqua.operators.gradients.Hessian.convert "qiskit.aqua.operators.gradients.Hessian.convert")(operator\[, params]) | **type operator**`OperatorBase` |
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| [`get_hessian`](#qiskit.aqua.operators.gradients.Hessian.get_hessian "qiskit.aqua.operators.gradients.Hessian.get_hessian")(operator\[, params]) | Get the Hessian for the given operator w\.r.t. |
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| [`gradient_wrapper`](#qiskit.aqua.operators.gradients.Hessian.gradient_wrapper "qiskit.aqua.operators.gradients.Hessian.gradient_wrapper")(operator, bind\_params\[, …]) | Get a callable function which provides the respective gradient, Hessian or QFI for given parameter values. |
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| [`parameter_expression_grad`](#qiskit.aqua.operators.gradients.Hessian.parameter_expression_grad "qiskit.aqua.operators.gradients.Hessian.parameter_expression_grad")(param\_expr, param) | Get the derivative of a parameter expression w\.r.t. |
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## Attributes
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| | |
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| --------------------------------------------------------------------------------------------------------------------------- | -------------------------- |
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| [`hess_method`](#qiskit.aqua.operators.gradients.Hessian.hess_method "qiskit.aqua.operators.gradients.Hessian.hess_method") | Returns `CircuitGradient`. |
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### convert
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<Function id="qiskit.aqua.operators.gradients.Hessian.convert" signature="convert(operator, params=None)">
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**Parameters**
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* **operator** (`OperatorBase`) – The operator for which we compute the Hessian
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* **params** (`Union`\[`Tuple`\[`ParameterExpression`, `ParameterExpression`], `List`\[`Tuple`\[`ParameterExpression`, `ParameterExpression`]], `List`\[`ParameterExpression`], `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.
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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.aqua.operators.OperatorBase "qiskit.aqua.operators.OperatorBase")
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**Raises**
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**ValueError** – If params is not set.
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</Function>
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### get\_hessian
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<Function id="qiskit.aqua.operators.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`) – Operator w\.r.t. which we take the Hessian.
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* **params** (`Union`\[`Tuple`\[`ParameterExpression`, `ParameterExpression`], `List`\[`Tuple`\[`ParameterExpression`, `ParameterExpression`]], `None`]) – Parameters w\.r.t. which we compute the Hessian.
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**Return type**
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`OperatorBase`
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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** – If `params` contains a parameter not present in `operator`.
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* [**AquaError**](qiskit.aqua.AquaError "qiskit.aqua.AquaError") – If the coefficient of the operator could not be reduced to 1. AquaError: If the differentiation of a combo\_fn requires JAX but the package is not installed.
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* **TypeError** – If the operator does not include a StateFn given by a quantum circuit
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* **TypeError** – If the parameters were given in an unsupported format.
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* **Exception** – Unintended code is reached
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</Function>
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### gradient\_wrapper
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<Function id="qiskit.aqua.operators.gradients.Hessian.gradient_wrapper" signature="gradient_wrapper(operator, bind_params, grad_params=None, backend=None)">
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Get a callable function which provides the respective gradient, Hessian or QFI for given parameter values. This callable can be used as gradient function for optimizers.
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**Parameters**
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* **operator** (`OperatorBase`) – The operator for which we want to get the gradient, Hessian or QFI.
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* **bind\_params** (`Union`\[`ParameterExpression`, `ParameterVector`, `List`\[`ParameterExpression`]]) – The operator parameters to which the parameter values are assigned.
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* **grad\_params** (`Union`\[`ParameterExpression`, `ParameterVector`, `List`\[`ParameterExpression`], `Tuple`\[`ParameterExpression`, `ParameterExpression`], `List`\[`Tuple`\[`ParameterExpression`, `ParameterExpression`]], `None`]) – The parameters with respect to which we are taking the gradient, Hessian or QFI. If grad\_params = None, then grad\_params = bind\_params
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* **backend** (`Union`\[`BaseBackend`, `QuantumInstance`, `None`]) – The quantum backend or QuantumInstance to use to evaluate the gradient, Hessian or QFI.
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**Returns**
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Function to compute a gradient, Hessian or QFI. The function takes an iterable as argument which holds the parameter values.
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**Return type**
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callable(param\_values)
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</Function>
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### hess\_method
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<Attribute id="qiskit.aqua.operators.gradients.Hessian.hess_method">
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Returns `CircuitGradient`.
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**Return type**
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`CircuitGradient`
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**Returns**
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`CircuitGradient`.
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</Attribute>
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### parameter\_expression\_grad
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<Function id="qiskit.aqua.operators.gradients.Hessian.parameter_expression_grad" signature="parameter_expression_grad(param_expr, param)" modifiers="static">
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Get the derivative of a parameter expression w\.r.t. the given parameter.
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**Parameters**
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* **param\_expr** (`ParameterExpression`) – The Parameter Expression for which we compute the derivative
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* **param** (`ParameterExpression`) – Parameter w\.r.t. which we want to take the derivative
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**Return type**
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`Union`\[`ParameterExpression`, `float`]
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**Returns**
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ParameterExpression representing the gradient of param\_expr w\.r.t. param
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</Function>
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</Class>
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