80 lines
3.2 KiB
Plaintext
80 lines
3.2 KiB
Plaintext
---
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title: VariationalPrinciple
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description: API reference for qiskit.algorithms.time_evolvers.variational.VariationalPrinciple
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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.algorithms.time_evolvers.variational.VariationalPrinciple
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---
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# VariationalPrinciple
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<Class id="qiskit.algorithms.time_evolvers.variational.VariationalPrinciple" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.23/qiskit/algorithms/time_evolvers/variational/variational_principles/variational_principle.py" signature="VariationalPrinciple(qgt, gradient)" modifiers="class">
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Bases: `abc.ABC`
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A Variational Principle class. It determines the time propagation of parameters in a quantum state provided as a parametrized quantum circuit (ansatz).
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### qgt
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<Attribute id="qiskit.algorithms.time_evolvers.variational.VariationalPrinciple.qgt">
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Instance of a class used to compute the GQT.
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**Type**
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[BaseQGT](qiskit.algorithms.gradients.BaseQGT "qiskit.algorithms.gradients.BaseQGT")
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</Attribute>
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### gradient
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<Attribute id="qiskit.algorithms.time_evolvers.variational.VariationalPrinciple.gradient">
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Instance of a class used to compute the state gradient.
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**Type**
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[BaseEstimatorGradient](qiskit.algorithms.gradients.BaseEstimatorGradient "qiskit.algorithms.gradients.BaseEstimatorGradient")
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</Attribute>
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**Parameters**
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* **qgt** ([`BaseQGT`](qiskit.algorithms.gradients.BaseQGT "qiskit.algorithms.gradients.base_qgt.BaseQGT")) – Instance of a class used to compute the GQT.
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* **gradient** ([`BaseEstimatorGradient`](qiskit.algorithms.gradients.BaseEstimatorGradient "qiskit.algorithms.gradients.base_estimator_gradient.BaseEstimatorGradient")) – Instance of a class used to compute the state gradient.
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## Methods Defined Here
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### evolution\_gradient
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<Function id="qiskit.algorithms.time_evolvers.variational.VariationalPrinciple.evolution_gradient" signature="VariationalPrinciple.evolution_gradient(hamiltonian, ansatz, param_values, gradient_params=None)" modifiers="abstract">
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Calculates an evolution gradient according to the rules of this variational principle.
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**Parameters**
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* **hamiltonian** – Operator used for Variational Quantum Time Evolution.
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* **ansatz** – Quantum state in the form of a parametrized quantum circuit.
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* **param\_values** – Values of parameters to be bound.
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* **gradient\_params** – List of parameters with respect to which gradients should be computed. If `None` given, gradients w\.r.t. all parameters will be computed.
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**Returns**
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An evolution gradient.
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</Function>
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### metric\_tensor
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<Function id="qiskit.algorithms.time_evolvers.variational.VariationalPrinciple.metric_tensor" signature="VariationalPrinciple.metric_tensor(ansatz, param_values)">
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Calculates a metric tensor according to the rules of this variational principle.
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**Parameters**
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* **ansatz** – Quantum state in the form of a parametrized quantum circuit.
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* **param\_values** – Values of parameters to be bound.
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**Returns**
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Metric tensor.
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**Raises**
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[**AlgorithmError**](qiskit.algorithms.AlgorithmError "qiskit.algorithms.AlgorithmError") – If a QFI job fails.
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</Function>
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</Class>
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