qiskit.opflow.state_fns.CVaRMeasurement¶

class
CVaRMeasurement
(primitive=None, alpha=1.0, coeff=1.0)[Quellcode]¶  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. Parameter
primitive (
Optional
[OperatorBase
]) – TheOperatorBase
which defines the diagonal operator measurement.coeff (
Union
[complex
,ParameterExpression
]) – A coefficient by which to multiply the state functionalpha (
float
) – A realvalued 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
 Verursacht
ValueError – TODO remove that this raises an error
ValueError – If alpha is not in [0, 1].
OpflowError – If the primitive is not diagonal.

__init__
(primitive=None, alpha=1.0, coeff=1.0)[Quellcode]¶  Parameter
primitive (
Optional
[OperatorBase
]) – TheOperatorBase
which defines the diagonal operator measurement.coeff (
Union
[complex
,ParameterExpression
]) – A coefficient by which to multiply the state functionalpha (
float
) – A realvalued 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
 Verursacht
ValueError – TODO remove that this raises an error
ValueError – If alpha is not in [0, 1].
OpflowError – If the primitive is not diagonal.
Methods
__init__
([primitive, alpha, coeff]) type primitive
Optional
[OperatorBase
]
add
(other)Return Operator addition of self and other, overloaded by
+
.adjoint
()The adjoint of a CVaRMeasurement is not defined.
assign_parameters
(param_dict)Binds scalar values to any Terra
Parameters
in the coefficients or primitives of the Operator, or substitutes oneParameter
for another.bind_parameters
(param_dict)Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters).
compose
(other[, permutation, front])Composition (Linear algebrastyle: 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
(energies, probabilities)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.
copy
()Return a deep copy of the Operator.
equals
(other)Evaluate Equality between Operators, overloaded by
==
.eval
([front])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
([front])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
([front])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
(scalar)Returns the scalar multiplication of the Operator, overloaded by
*
, including support for Terra’sParameters
, which can be bound to values later (viabind_parameters
).neg
()Return the Operator’s negation, effectively just multiplying by 1.0, overloaded by

.permute
(permutation)Permute the qubits of the state function.
power
(exponent)Compose with Self Multiple Times, undefined for StateFns.
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
([shots, massive, reverse_endianness])Sample the state function as a normalized probability distribution.
tensor
(other)Return tensor product between self and other, overloaded by
^
.tensorpower
(other)Return tensor product with self multiple times, overloaded by
^
.Not defined.
to_density_matrix
([massive])Not defined.
to_matrix
([massive])Not defined.
to_matrix_op
([massive])Not defined.
Return SciPy sparse matrix representation of the Operator.
traverse
(convert_fn[, coeff])Apply the convert_fn to the internal primitive if the primitive is an Operator (as in the case of
OperatorStateFn
).Attributes
INDENTATION
A realvalued parameter between 0 and 1 which specifies the
A coefficient by which the state function is multiplied.
Return the unique instance id.
Whether the StateFn object is a measurement Operator.
The number of qubits over which the Operator is defined.
Return a set of Parameter objects contained in the Operator.
The primitive which defines the behavior of the underlying State function.
Return settings.

add
(other)[Quellcode]¶ Return Operator addition of self and other, overloaded by
+
. Parameter
other (
OperatorBase
) – AnOperatorBase
with the same number of qubits as self, and in the same ‚Operator‘, ‚State function‘, or ‚Measurement‘ category as self (i.e. the same type of underlying function). Rückgabetyp
SummedOp
 Rückgabe
An
OperatorBase
equivalent to the sum of self and other.

adjoint
()[Quellcode]¶ The adjoint of a CVaRMeasurement is not defined.
 Rückgabe
Does not return anything, raises an error.
 Verursacht
OpflowError – The adjoint of a CVaRMeasurement is not defined.

property
alpha
¶  A realvalued 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.
 Rückgabetyp
float
 Rückgabe
The parameter alpha which was given at initialization

assign_parameters
(param_dict)¶ Binds scalar values to any Terra
Parameters
in the coefficients or primitives of the Operator, or substitutes oneParameter
for another. This method differs from Terra’sassign_parameters
in that it also supports lists of values to assign for a giveParameter
, in which case self will be copied for each parameterization in the binding list(s), and all the copies will be returned in anOpList
. If lists of parameterizations are used, everyParameter
in the param_dict must have the same length list of parameterizations. Parameter
param_dict (
dict
) – The dictionary ofParameters
to replace, and values or lists of values by which to replace them. Rückgabetyp
OperatorBase
 Rückgabe
The
OperatorBase
with theParameters
in self replaced by the values orParameters
in param_dict. If param_dict contains parameterization lists, thisOperatorBase
is anOpList
.

bind_parameters
(param_dict)¶ Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters).
 Rückgabetyp
OperatorBase

property
coeff
¶ A coefficient by which the state function is multiplied.
 Rückgabetyp
Union
[complex
,ParameterExpression
]

compose
(other, permutation=None, front=False)¶ Composition (Linear algebrastyle: A@B(x) = A(B(x))) is not well defined for states in the binary function model, but is well defined for measurements.
 Parameter
other (
OperatorBase
) – The Operator to compose with self.permutation (
Optional
[List
[int
]]) –List[int]
which defines permutation on other operator.front (
bool
) – If front==True, returnother.compose(self)
.
 Rückgabetyp
OperatorBase
 Rückgabe
An Operator equivalent to the function composition of self and other.
 Verursacht
ValueError – If self is not a measurement, it cannot be composed from the right.

compute_cvar
(energies, probabilities)[Quellcode]¶ 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. Note that the sampling probabilities serve as an alternative to knowing the counts of each observation and that the input energies are assumed to be sorted in increasing order.
Consider the outcome with index j, such that only some of the samples with measurement outcome j will be used in computing CVaR. The CVaR calculation can then be separated into two parts. First we sum each of the energies for outcomes i < j, weighted by the probability of observing that outcome (i.e the normalized counts). Second, we add the energy for outcome j, weighted by the difference (α  sum_i<j p_i)
 Parameter
energies (
list
) – A list containing the energies (H_i) of each sample measurement outcome, sorted in increasing order.probabilities (
list
) – The sampling probabilities (p_i) for each corresponding measurement outcome.
 Rückgabetyp
complex
 Rückgabe
 The CVaR of the diagonal observable specified by self.primitive and
the sampled quantum state described by the inputs (energies, probabilities). For index j (described above), the CVaR is computed as H_j + 1/α * (sum_i<j p_i*(H_i  H_j))
 Verursacht
ValueError – front isn’t a DictStateFn or VectorStateFn

copy
()¶ Return a deep copy of the Operator.
 Rückgabetyp
OperatorBase

equals
(other)¶ Evaluate Equality between Operators, overloaded by
==
. Only returns True if self and other are of the same representation (e.g. a DictStateFn and CircuitStateFn will never be equal, even if their vector representations are equal), their underlying primitives are equal (this means for ListOps, OperatorStateFns, or EvolvedOps the equality is evaluated recursively downwards), and their coefficients are equal. Parameter
other (
OperatorBase
) – TheOperatorBase
to compare to self. Rückgabetyp
bool
 Rückgabe
A bool equal to the equality of self and other.

eval
(front=None)[Quellcode]¶ 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)). Note that index j corresponds to the measurement outcome such that only some of the samples with measurement outcome j will be used in computing CVaR. Note also that the sampling probabilities serve as an alternative to knowing the counts of each observation.
This computation is broken up into two subroutines. One which evaluates each measurement outcome and determines the sampling probabilities of each. And one which carries out the above calculation. The computation is split up this way to enable a straightforward calculation of the variance of this estimator.
 Parameter
front (
Union
[str
,dict
,ndarray
,OperatorBase
,Statevector
,None
]) – A StateFn or primitive which specifies the results of evaluating a quantum state. Rückgabetyp
complex
 Rückgabe
 The CVaR of the diagonal observable specified by self.primitive and
the sampled quantum state described by the inputs (energies, probabilities). For index j (described above), the CVaR is computed as H_j + 1/α*(sum_i<j p_i*(H_i  H_j))

eval_variance
(front=None)[Quellcode]¶ 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)). This follows from the definition that Var[X] = E[X^2]  E[X]^2. In this case, X = E[<biHbi>], where H is the diagonal observable and bi corresponds to measurement outcome i. Given this, E[X^2] = E[<biHbi>^2]
 Parameter
front (
Union
[str
,dict
,ndarray
,OperatorBase
,None
]) – A StateFn or primitive which specifies the results of evaluating a quantum state. Rückgabetyp
complex
 Rückgabe
 The Var[CVaR] of the diagonal observable specified by self.primitive
and the sampled quantum state described by the inputs (energies, probabilities). For index j (described above), the CVaR is computed as H_j^2 + 1/α*(sum_i<j p_i*(H_i^2  H_j^2))

get_outcome_energies_probabilities
(front=None)[Quellcode]¶ 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. Note that the counts for each measurement outcome will also suffice (and this is often how the CVaR is presented).
 Parameter
front (
Union
[str
,dict
,ndarray
,OperatorBase
,Statevector
,None
]) – A StateFn or a primitive which defines a StateFn. This input holds the results of a sampled/simulated circuit. Rückgabetyp
Tuple
[list
,list
] Rückgabe
 Two lists of equal length. energies contains the energy of each
unique measurement outcome computed against the diagonal observable stored in self.primitive. probabilities contains the corresponding sampling probability for each measurement outcome in energies.
 Verursacht
ValueError – front isn’t a DictStateFn or VectorStateFn

property
instance_id
¶ Return the unique instance id.
 Rückgabetyp
int

property
is_measurement
¶ Whether the StateFn object is a measurement Operator.
 Rückgabetyp
bool

mul
(scalar)[Quellcode]¶ Returns the scalar multiplication of the Operator, overloaded by
*
, including support for Terra’sParameters
, which can be bound to values later (viabind_parameters
). Parameter
scalar (
Union
[complex
,ParameterExpression
]) – The real or complex scalar by which to multiply the Operator, or theParameterExpression
to serve as a placeholder for a scalar factor. Rückgabetyp
CVaRMeasurement
 Rückgabe
An
OperatorBase
equivalent to product of self and scalar.

neg
()¶ Return the Operator’s negation, effectively just multiplying by 1.0, overloaded by

. Rückgabetyp
OperatorBase
 Rückgabe
An
OperatorBase
equivalent to the negation of self.

property
num_qubits
¶ The number of qubits over which the Operator is defined. If
op.num_qubits == 5
, thenop.eval('1' * 5)
will be valid, butop.eval('11')
will not. Rückgabetyp
int
 Rückgabe
The number of qubits accepted by the Operator’s underlying function.

property
parameters
¶ Return a set of Parameter objects contained in the Operator.

permute
(permutation)¶ Permute the qubits of the state function.
 Parameter
permutation (
List
[int
]) – A list defining where each qubit should be permuted. The qubit at index j of the circuit should be permuted to position permutation[j]. Rückgabetyp
OperatorStateFn
 Rückgabe
A new StateFn containing the permuted primitive.

power
(exponent)¶ Compose with Self Multiple Times, undefined for StateFns.
 Parameter
exponent (
int
) – The number of times to compose self with self. Verursacht
ValueError – This function is not defined for StateFns.
 Rückgabetyp
OperatorBase

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

primitive_strings
()¶ Return a set of strings describing the primitives contained in the Operator. For example,
{'QuantumCircuit', 'Pauli'}
. For hierarchical Operators, such asListOps
, this can help illuminate the primitives represented in the various recursive levels, and therefore which conversions can be applied. Rückgabetyp
Set
[str
] Rückgabe
A set of strings describing the primitives contained within the Operator.

reduce
()¶ Try collapsing the Operator structure, usually after some type of conversion, e.g. trying to add Operators in a SummedOp or delete needless IGates in a CircuitOp. If no reduction is available, just returns self.
 Rückgabetyp
OperatorBase
 Rückgabe
The reduced
OperatorBase
.

sample
(shots=1024, massive=False, reverse_endianness=False)[Quellcode]¶ Sample the state function as a normalized probability distribution. Returns dict of bitstrings in order of probability, with values being probability.
 Parameter
shots (
int
) – The number of samples to take to approximate the State function.massive (
bool
) – Whether to allow large conversions, e.g. creating a matrix representing over 16 qubits.reverse_endianness (
bool
) – Whether to reverse the endianness of the bitstrings in the return dict to match Terra’s bigendianness.
 Rückgabe
A dict containing pairs sampled strings from the State function and sampling frequency divided by shots.

property
settings
¶ Return settings.
 Rückgabetyp
Dict

tensor
(other)[Quellcode]¶ Return tensor product between self and other, overloaded by
^
. Note: You must be conscious of Qiskit’s bigendian bit printing convention. Meaning, Plus.tensor(Zero) produces a +⟩ on qubit 0 and a 0⟩ on qubit 1, or +⟩⨂0⟩, but would produce a QuantumCircuit like0⟩– +⟩–
Because Terra prints circuits and results with qubit 0 at the end of the string or circuit.
 Parameter
other (
OperatorBase
) – TheOperatorBase
to tensor product with self. Rückgabetyp
Union
[OperatorStateFn
,TensoredOp
] Rückgabe
An
OperatorBase
equivalent to the tensor product of self and other.

tensorpower
(other)¶ Return tensor product with self multiple times, overloaded by
^
. Parameter
other (
int
) – The int number of times to tensor product self with itself viatensorpower
. Rückgabetyp
Union
[OperatorBase
,int
] Rückgabe
An
OperatorBase
equivalent to the tensorpower of self by other.

to_circuit_op
()[Quellcode]¶ Not defined.

to_density_matrix
(massive=False)[Quellcode]¶ Not defined.

to_matrix
(massive=False)[Quellcode]¶ Not defined.

to_matrix_op
(massive=False)[Quellcode]¶ Not defined.

to_spmatrix
()¶ Return SciPy sparse matrix representation of the Operator. Represents the evaluation of the Operator’s underlying function on every combination of basis binary strings.
 Rückgabetyp
spmatrix
 Rückgabe
The SciPy
spmatrix
equivalent to this Operator.

traverse
(convert_fn, coeff=None)[Quellcode]¶ Apply the convert_fn to the internal primitive if the primitive is an Operator (as in the case of
OperatorStateFn
). Otherwise do nothing. Used by converters. Parameter
convert_fn (
Callable
) – The function to apply to the internal OperatorBase.coeff (
Union
[complex
,ParameterExpression
,None
]) – A coefficient to multiply by after applying convert_fn. If it is None, self.coeff is used instead.
 Rückgabetyp
OperatorBase
 Rückgabe
The converted StateFn.