Hessian

class Hessian(hess_method='param_shift', **kwargs)

Compute the Hessian of an expected value.

Parameters

hess_method (Union[str, 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.
kwargs (dict) – Optional parameters for a CircuitGradient

Raises

ValueError – If method != fin_diff and epsilon is not None.

Methods Defined Here

Hessian.convert(operator, params=None)

Parameters

operator (OperatorBase) – The operator for which we compute the Hessian
params (Union[Tuple[ParameterExpression, ParameterExpression], List[Tuple[ParameterExpression, ParameterExpression]], List[ParameterExpression], ParameterVector, None]) – The parameters we are computing the Hessian with respect to Either give directly the tuples/list of tuples for which the second order derivative is to be computed or give a list of parameters to build the full Hessian for those parameters. If not explicitly passed, the full Hessian is constructed. The parameters are then inferred from the operator and sorted by name.

Returns

An operator whose evaluation yields the Hessian

Return type

OperatorBase

Hessian.get_hessian(operator, params=None)

Get the Hessian for the given operator w.r.t. the given parameters

Parameters

operator (OperatorBase) – Operator w.r.t. which we take the Hessian.
params (Union[Tuple[ParameterExpression, ParameterExpression], List[Tuple[ParameterExpression, ParameterExpression]], List[ParameterExpression], ParameterVector, None]) – Parameters w.r.t. which we compute the Hessian. If not explicitly passed, the full Hessian is constructed. The parameters are then inferred from the operator and sorted by name.

Return type

OperatorBase

Returns

Operator which represents the gradient w.r.t. the given params.

Raises

ValueError – If params contains a parameter not present in operator.
ValueError – If operator is not parameterized.
OpflowError – If the coefficient of the operator could not be reduced to 1.
OpflowError – If the differentiation of a combo_fn requires JAX but the package is not installed.
TypeError – If the operator does not include a StateFn given by a quantum circuit
TypeError – If the parameters were given in an unsupported format.
Exception – Unintended code is reached
MissingOptionalLibraryError – jax not installed

Returns CircuitGradient.

Return type

CircuitGradient

Returns

CircuitGradient.

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