qiskit.opflow.gradients.DerivativeBase

class DerivativeBase

Base class for differentiating opflow objects.

Converter for differentiating opflow objects and handling things like properly differentiating combo_fn’s and enforcing product rules when operator coefficients are parameterized.

This is distinct from CircuitGradient converters which use quantum techniques such as parameter shifts and linear combination of unitaries to compute derivatives of circuits.

CircuitGradient - uses quantum techniques to get derivatives of circuits DerivativeBase - uses classical techniques to differentiate opflow data structures

__init__()

Initialize self. See help(type(self)) for accurate signature.

Methods

__init__()	Initialize self.
convert(operator[, params])	type operator OperatorBase
gradient_wrapper(operator, bind_params[, …])	Get a callable function which provides the respective gradient, Hessian or QFI for given parameter values.
parameter_expression_grad(param_expr, param)	Get the derivative of a parameter expression w.r.t.

abstract convert(operator, params=None)

Parameters

• operator (OperatorBase) – The operator we are taking the gradient, Hessian or QFI of

• params (Union[ParameterVector, ParameterExpression, List[ParameterExpression], None]) – The parameters we are taking the gradient, Hessian or QFI with respect to.

Return type

OperatorBase

Returns

An operator whose evaluation yields the gradient, Hessian or QFI.

Raises

ValueError – If params contains a parameter not present in operator.

gradient_wrapper(operator, bind_params, grad_params=None, backend=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[BaseBackend, QuantumInstance, None]) – The quantum backend or QuantumInstance to use to evaluate the gradient, Hessian or QFI.

Returns

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

Return type

callable(param_values)

static parameter_expression_grad(param_expr, param)

Get the derivative of a parameter expression w.r.t. the given parameter.

Parameters

• param_expr (ParameterExpression) – The Parameter Expression for which we compute the derivative

• param (ParameterExpression) – Parameter w.r.t. which we want to take the derivative

Return type

Union[ParameterExpression, float]

Returns

ParameterExpression representing the gradient of param_expr w.r.t. param