94 lines
4.4 KiB
Plaintext
94 lines
4.4 KiB
Plaintext
---
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title: Gradient
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description: API reference for qiskit.opflow.gradients.Gradient
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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.Gradient
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---
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# Gradient
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<Class id="qiskit.opflow.gradients.Gradient" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.22/qiskit/opflow/gradients/gradient.py" signature="Gradient(grad_method='param_shift', **kwargs)" modifiers="class">
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Bases: [`qiskit.opflow.gradients.gradient_base.GradientBase`](qiskit.opflow.gradients.GradientBase "qiskit.opflow.gradients.gradient_base.GradientBase")
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Convert an operator expression to the first-order gradient.
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**Parameters**
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* **grad\_method** (`Union`\[`str`, [`CircuitGradient`](qiskit.opflow.gradients.CircuitGradient "qiskit.opflow.gradients.circuit_gradients.circuit_gradient.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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## Methods Defined Here
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### convert
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<Function id="qiskit.opflow.gradients.Gradient.convert" signature="Gradient.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 we are taking the gradient of.
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* **params** (`Union`\[[`ParameterVector`](qiskit.circuit.ParameterVector "qiskit.circuit.parametervector.ParameterVector"), [`ParameterExpression`](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression"), `List`\[[`ParameterExpression`](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")], `None`]) – The parameters we are taking the gradient with respect to. If not explicitly passed, they are inferred from the operator and sorted by name.
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**Return type**
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[`OperatorBase`](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.OperatorBase")
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**Returns**
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An operator whose evaluation yields the Gradient.
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**Raises**
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* **ValueError** – If `params` contains a parameter not present in `operator`.
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* **ValueError** – If `operator` is not parameterized.
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</Function>
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### get\_gradient
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<Function id="qiskit.opflow.gradients.Gradient.get_gradient" signature="Gradient.get_gradient(operator, params)">
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Get the gradient 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 gradient.
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* **params** (`Union`\[[`ParameterExpression`](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression"), [`ParameterVector`](qiskit.circuit.ParameterVector "qiskit.circuit.parametervector.ParameterVector"), `List`\[[`ParameterExpression`](qiskit.circuit.ParameterExpression "qiskit.circuit.parameterexpression.ParameterExpression")]]) – Parameters w\.r.t. which we compute the gradient.
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**Return type**
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[`OperatorBase`](qiskit.opflow.OperatorBase "qiskit.opflow.operator_base.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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* [**OpflowError**](qiskit.opflow.OpflowError "qiskit.opflow.OpflowError") – If the coefficient of the operator could not be reduced to 1.
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* [**OpflowError**](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** – If the operator does not include a StateFn given by a quantum circuit
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* **Exception** – Unintended code is reached
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* **MissingOptionalLibraryError** – jax not installed
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</Function>
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## Attributes
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### grad\_method
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<Attribute id="qiskit.opflow.gradients.Gradient.grad_method">
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Returns `CircuitGradient`.
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**Return type**
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[`CircuitGradient`](qiskit.opflow.gradients.CircuitGradient "qiskit.opflow.gradients.circuit_gradients.circuit_gradient.CircuitGradient")
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**Returns**
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`CircuitGradient`.
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</Attribute>
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</Class>
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