ListOp

class ListOp(oplist, combo_fn=None, coeff=1.0, abelian=False, grad_combo_fn=None)

Bases: qiskit.opflow.operator_base.OperatorBase

A Class for manipulating List Operators, and parent class to SummedOp, ComposedOp, and TensoredOp.

List Operators are classes for storing and manipulating lists of Operators, State functions, or Measurements, and include some rule or combo_fn defining how the Operator functions of the list constituents should be combined to form to cumulative Operator function of the ListOp. For example, a SummedOp has an addition-based combo_fn, so once the Operators in its list are evaluated against some bitstring to produce a list of results, we know to add up those results to produce the final result of the SummedOp’s evaluation. In theory, this combo_fn can be any function over classical complex values, but for convenience we’ve chosen for them to be defined over NumPy arrays and values. This way, large numbers of evaluations, such as after calling to_matrix on the list constituents, can be efficiently combined. While the combination function is defined over classical values, it should be understood as the operation by which each Operators’ underlying function is combined to form the underlying Operator function of the ListOp. In this way, the ListOps are the basis for constructing large and sophisticated Operators, State Functions, and Measurements.

The base ListOp class is particularly interesting, as its combo_fn is “the identity list Operation”. Meaning, if we understand the combo_fn as a function from a list of complex values to some output, one such function is returning the list as-is. This is powerful for constructing compact hierarchical Operators which return many measurements in multiple dimensional lists.

Parameters

• oplist (Sequence[OperatorBase]) – The list of OperatorBases defining this Operator’s underlying function.

• combo_fn (Optional[Callable]) – The recombination function to combine classical results of the oplist Operators’ eval functions (e.g. sum). Default is lambda x: x.

• coeff (Union[complex, ParameterExpression]) – A coefficient multiplying the operator

• abelian (bool) – Indicates whether the Operators in oplist are known to mutually commute.

• grad_combo_fn (Optional[Callable]) – The gradient of recombination function. If None, the gradient will be computed automatically.

• the (Note that the default "recombination function" lambda above is essentially) –

• values (identity - it accepts the list of) –

• list. (and returns them in a) –

Methods Defined Here

add	Return Operator addition of self and other, overloaded by +.
adjoint	Return a new Operator equal to the Operator's adjoint (conjugate transpose), overloaded by ~.
assign_parameters	Binds scalar values to any Terra Parameters in the coefficients or primitives of the Operator, or substitutes one Parameter for another.
compose	Return Operator Composition between self and other (linear algebra-style: A@B(x) = A(B(x))), overloaded by @.
default_combo_fn	ListOp default combo function i.e. lambda x: x.
equals	Evaluate Equality between Operators, overloaded by ==.
eval	Evaluate the Operator's underlying function, either on a binary string or another Operator.
exp_i	Return an OperatorBase equivalent to an exponentiation of self * -i, e^(-i*op).
log_i	Return a MatrixOp equivalent to log(H)/-i for this operator H.
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).
permute	Permute the qubits of the operator.
power	Return Operator composed with self multiple times, overloaded by **.
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.
tensor	Return tensor product between self and other, overloaded by ^.
tensorpower	Return tensor product with self multiple times, overloaded by ^.
to_circuit_op	Returns an equivalent Operator composed of only QuantumCircuit-based primitives, such as CircuitOp and CircuitStateFn.
to_matrix	Return NumPy representation of the Operator.
to_matrix_op	Returns an equivalent Operator composed of only NumPy-based primitives, such as MatrixOp and VectorStateFn.
to_pauli_op	Returns an equivalent Operator composed of only Pauli-based primitives, such as PauliOp.
to_spmatrix	Returns SciPy sparse matrix representation of the Operator.
traverse	Apply the convert_fn to each node in the oplist.

Attributes

INDENTATION = '  '

abelian

Whether the Operators in oplist are known to commute with one another.

Return type

bool

Returns

A bool indicating whether the oplist is Abelian.

coeff

The scalar coefficient multiplying the Operator.

Return type

Union[complex, ParameterExpression]

Returns

The coefficient.

coeffs

Return a list of the coefficients of the operators listed. Raises exception for nested Listops.

Return type

List[Union[complex, ParameterExpression]]

combo_fn

The function defining how to combine oplist (or Numbers, or NumPy arrays) to produce the Operator’s underlying function. For example, SummedOp’s combination function is to add all of the Operators in oplist.

Return type

Callable

Returns

The combination function.

distributive

Indicates whether the ListOp or subclass is distributive under composition. ListOp and SummedOp are, meaning that (opv @ op) = (opv[0] @ op + opv[1] @ op) (using plus for SummedOp, list for ListOp, etc.), while ComposedOp and TensoredOp do not behave this way.

Return type

bool

Returns

A bool indicating whether the ListOp is distributive under composition.

grad_combo_fn

The gradient of combo_fn.

Return type

Optional[Callable]

instance_id

Return the unique instance id.

Return type

int

num_qubits

Return type

int

oplist

The list of OperatorBases defining the underlying function of this Operator.

Return type

List[OperatorBase]

Returns

The Operators defining the ListOp

parameters

settings

Return settings.

Return type

Dict