110 lines
4.3 KiB
Plaintext
110 lines
4.3 KiB
Plaintext
---
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title: QFIBase
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description: API reference for qiskit.aqua.operators.gradients.QFIBase
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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.QFIBase
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---
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# QFIBase
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<Class id="qiskit.aqua.operators.gradients.QFIBase" isDedicatedPage={true} github="https://github.com/qiskit-community/qiskit-aqua/tree/stable/0.9/qiskit/aqua/operators/gradients/qfi_base.py" signature="QFIBase(qfi_method='lin_comb_full')" modifiers="class">
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Bases: `qiskit.aqua.operators.gradients.derivative_base.DerivativeBase`
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Base class for Quantum Fisher Information (QFI).
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Compute the Quantum Fisher Information (QFI) given a pure, parametrized quantum state.
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The QFI is:
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> \[QFI]kl= Re\[〈∂kψ|∂lψ〉−〈∂kψ|ψ〉〈ψ|∂lψ〉] \* 4.
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**Parameters**
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**qfi\_method** (`Union`\[`str`, `CircuitQFI`]) – The method used to compute the state/probability gradient. Can be either a [`CircuitQFI`](qiskit.aqua.operators.gradients.CircuitQFI "qiskit.aqua.operators.gradients.CircuitQFI") instance or one of the following pre-defined strings `'lin_comb_full'`, `` 'overlap_diag'` `` or `` 'overlap_block_diag'` ``.
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**Raises**
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**ValueError** – if `qfi_method` is neither a `CircuitQFI` object nor one of the predefined strings.
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## Methods
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### convert
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<Function id="qiskit.aqua.operators.gradients.QFIBase.convert" signature="QFIBase.convert(operator, params=None)" modifiers="abstract">
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**Parameters**
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* **operator** (`OperatorBase`) – The operator we are taking the gradient, Hessian or QFI of
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* **params** (`Union`\[`ParameterVector`, `ParameterExpression`, `List`\[`ParameterExpression`], `None`]) – The parameters we are taking the gradient, Hessian or QFI with respect to.
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**Return type**
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`OperatorBase`
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**Returns**
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An operator whose evaluation yields the gradient, Hessian or QFI.
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**Raises**
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**ValueError** – If `params` contains a parameter not present in `operator`.
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</Function>
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### gradient\_wrapper
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<Function id="qiskit.aqua.operators.gradients.QFIBase.gradient_wrapper" signature="QFIBase.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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### parameter\_expression\_grad
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<Function id="qiskit.aqua.operators.gradients.QFIBase.parameter_expression_grad" signature="QFIBase.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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## Attributes
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### qfi\_method
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<Attribute id="qiskit.aqua.operators.gradients.QFIBase.qfi_method">
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Returns `CircuitQFI`.
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**Return type**
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`CircuitQFI`
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**Returns**
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`CircuitQFI`.
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</Attribute>
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</Class>
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