CVaRMeasurement¶

class CVaRMeasurement(primitive=None, alpha=1.0, coeff=1.0)[source]¶

Bases: qiskit.aqua.operators.state_fns.operator_state_fn.OperatorStateFn

A specialized measurement class to compute CVaR expectation values.: See https://arxiv.org/pdf/1907.04769.pdf for further details.

Used in CVaRExpectation, see there for more details.

Parameters

primitive (Optional[OperatorBase]) – The OperatorBase which defines the diagonal operator measurement.
coeff (Union[int, float, complex, ParameterExpression]) – A coefficient by which to multiply the state function
alpha (float) – A real-valued parameter between 0 and 1 which specifies the fraction of observed samples to include when computing the objective value. alpha = 1 corresponds to a standard observable expectation value. alpha = 0 corresponds to only using the single sample with the lowest energy. alpha = 0.5 corresponds to ranking each observation by lowest energy and using the best

Raises

ValueError – TODO remove that this raises an error
ValueError – If alpha is not in [0, 1].
AquaError – If the primitive is not diagonal.

Methods

`add`	Return Operator addition of self and other, overloaded by `+`.
`adjoint`	The adjoint of a CVaRMeasurement is not defined.
`assign_parameters`	Binds scalar values to any Terra `Parameters` in the coefficients or primitives of the Operator, or substitutes one `Parameter` for another.
`bind_parameters`	Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters).
`compose`	Composition (Linear algebra-style: A@B(x) = A(B(x))) is not well defined for states in the binary function model, but is well defined for measurements.
`compute_cvar`	Given the energies of each sampled measurement outcome (H_i) as well as the sampling probability of each measurement outcome (p_i, we can compute the CVaR.
`equals`	Evaluate Equality between Operators, overloaded by `==`.
`eval`	Given the energies of each sampled measurement outcome (H_i) as well as the sampling probability of each measurement outcome (p_i, we can compute the CVaR as H_j + 1/α(sum_i<j p_i(H_i - H_j)).
`eval_variance`	Given the energies of each sampled measurement outcome (H_i) as well as the sampling probability of each measurement outcome (p_i, we can compute the variance of the CVaR estimator as H_j^2 + 1/α * (sum_i<j p_i*(H_i^2 - H_j^2)).
`get_outcome_energies_probabilities`	In order to compute the CVaR of an observable expectation, we require the energies of each sampled measurement outcome as well as the sampling probability of each measurement outcome.
`mul`	Returns the scalar multiplication of the Operator, overloaded by `*`, including support for Terra’s `Parameters`, which can be bound to values later (via `bind_parameters`).
`neg`	Return the Operator’s negation, effectively just multiplying by -1.0, overloaded by `-`.
`permute`	Permute the qubits of the state function.
`power`	Compose with Self Multiple Times, undefined for StateFns.
`primitive_strings`	Return a set of strings describing the primitives contained in the Operator.
`reduce`	Try collapsing the Operator structure, usually after some type of conversion, e.g.
`sample`	Sample the state function as a normalized probability distribution.
`tensor`	Return tensor product between self and other, overloaded by `^`.
`tensorpower`	Return tensor product with self multiple times, overloaded by `^`.
`to_circuit_op`	Not defined.
`to_density_matrix`	Not defined.
`to_legacy_op`	Attempt to return the Legacy Operator representation of the Operator.
`to_matrix`	Not defined.
`to_matrix_op`	Not defined.
`traverse`	Apply the convert_fn to the internal primitive if the primitive is an Operator (as in the case of `OperatorStateFn`).

Attributes

ENABLE_DEPRECATION = True¶

INDENTATION = ' '¶

alpha¶

A real-valued parameter between 0 and 1 which specifies the: fraction of observed samples to include when computing the objective value. alpha = 1 corresponds to a standard observable expectation value. alpha = 0 corresponds to only using the single sample with the lowest energy. alpha = 0.5 corresponds to ranking each observation by lowest energy and using the best half.

Return type: float
Returns: The parameter alpha which was given at initialization

coeff¶

A coefficient by which the state function is multiplied.

Return type: Union[int, float, complex, ParameterExpression]

is_measurement¶

Whether the StateFn object is a measurement Operator.

Return type: bool

num_qubits¶

Return type: int

parameters¶

primitive¶: The primitive which defines the behavior of the underlying State function.