95 lines
3.3 KiB
Plaintext
95 lines
3.3 KiB
Plaintext
---
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title: LinearSystemObservable
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description: API reference for qiskit.algorithms.linear_solvers.LinearSystemObservable
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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.linear_solvers.LinearSystemObservable
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---
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# LinearSystemObservable
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<Class id="qiskit.algorithms.linear_solvers.LinearSystemObservable" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.21/qiskit/algorithms/linear_solvers/observables/linear_system_observable.py" signature="LinearSystemObservable" modifiers="class">
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Bases: `abc.ABC`
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An abstract class for linear system observables in Qiskit.
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## Methods
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### evaluate\_classically
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<Function id="qiskit.algorithms.linear_solvers.LinearSystemObservable.evaluate_classically" signature="LinearSystemObservable.evaluate_classically(solution)" modifiers="abstract">
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#### Calculates the analytical value of the given observable from the solution vector to the
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linear system.
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**Parameters**
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**solution** (`Union`\[`array`, [`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")]) – The solution to the system as a numpy array or the circuit that prepares it.
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**Return type**
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`float`
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**Returns**
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The value of the observable.
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</Function>
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### observable
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<Function id="qiskit.algorithms.linear_solvers.LinearSystemObservable.observable" signature="LinearSystemObservable.observable(num_qubits)" modifiers="abstract">
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The observable operator.
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**Parameters**
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**num\_qubits** (`int`) – The number of qubits on which the observable will be applied.
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**Return type**
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`Union`\[[`TensoredOp`](qiskit.opflow.list_ops.TensoredOp "qiskit.opflow.list_ops.tensored_op.TensoredOp"), `List`\[[`TensoredOp`](qiskit.opflow.list_ops.TensoredOp "qiskit.opflow.list_ops.tensored_op.TensoredOp")]]
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**Returns**
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The observable as a sum of Pauli strings.
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</Function>
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### observable\_circuit
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<Function id="qiskit.algorithms.linear_solvers.LinearSystemObservable.observable_circuit" signature="LinearSystemObservable.observable_circuit(num_qubits)" modifiers="abstract">
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The circuit implementing the observable.
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**Parameters**
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**num\_qubits** (`int`) – The number of qubits on which the observable will be applied.
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**Return type**
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`Union`\[[`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit"), `List`\[[`QuantumCircuit`](qiskit.circuit.QuantumCircuit "qiskit.circuit.quantumcircuit.QuantumCircuit")]]
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**Returns**
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The observable as a QuantumCircuit.
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</Function>
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### post\_processing
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<Function id="qiskit.algorithms.linear_solvers.LinearSystemObservable.post_processing" signature="LinearSystemObservable.post_processing(solution, num_qubits, scaling=1)" modifiers="abstract">
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Evaluates the given observable on the solution to the linear system.
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**Parameters**
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* **solution** (`Union`\[`float`, `List`\[`float`]]) – The probability calculated from the circuit and the observable.
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* **num\_qubits** (`int`) – The number of qubits where the observable was applied.
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* **scaling** (`float`) – Scaling of the solution.
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**Return type**
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`float`
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**Returns**
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The value of the observable.
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</Function>
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</Class>
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