qiskit.opflow.gradients.DerivativeBase.gradient_wrapper

DerivativeBase.gradient_wrapper(operator, bind_params, grad_params=None, backend=None, expectation=None)

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.

Parameters

• operator (OperatorBase) – The operator for which we want to get the gradient, Hessian or QFI.

• bind_params (Union[ParameterExpression, ParameterVector, List[ParameterExpression]]) – The operator parameters to which the parameter values are assigned.

• 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

• backend (Union[Backend, BaseBackend, QuantumInstance, None]) – The quantum backend or QuantumInstance to use to evaluate the gradient, Hessian or QFI.

• expectation (Optional[ExpectationBase]) – The expectation converter to be used. If none is set then PauliExpectation() is used.

Return type

Callable[[Iterable], ndarray]

Returns

Function to compute a gradient, Hessian or QFI. The function takes an iterable as argument which holds the parameter values.