ListOp
class qiskit.opflow.list_ops.ListOp(oplist, combo_fn=None, coeff=1.0, abelian=False, grad_combo_fn=None)
Bases: OperatorBase
Deprecated: 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.
The class qiskit.opflow.list_ops.list_op.ListOp is deprecated as of qiskit-terra 0.24.0. It will be removed in the Qiskit 1.0 release. For code migration guidelines, visit https://qisk.it/opflow_migration(opens in a new tab).
Parameters
- oplist (Sequence(opens in a new tab)[OperatorBase]) – The list of
OperatorBasesdefining this Operator’s underlying function. - combo_fn (Callable(opens in a new tab) | None) – The recombination function to combine classical results of the
oplistOperators’ eval functions (e.g. sum). Default is lambda x: x. - coeff (complex(opens in a new tab) |ParameterExpression) – A coefficient multiplying the operator
- abelian (bool(opens in a new tab)) – Indicates whether the Operators in
oplistare known to mutually commute. - grad_combo_fn (Callable(opens in a new tab) | None) – 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) –
Attributes
INDENTATION
Default value: ' '
abelian
Whether the Operators in oplist are known to commute with one another.
Returns
A bool indicating whether the oplist is Abelian.
coeff
The scalar coefficient multiplying the Operator.
Returns
The coefficient.
coeffs
Return a list of the coefficients of the operators listed. Raises exception for nested Listops.
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.
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.
Returns
A bool indicating whether the ListOp is distributive under composition.
grad_combo_fn
The gradient of combo_fn.
instance_id
Return the unique instance id.
num_qubits
oplist
The list of OperatorBases defining the underlying function of this Operator.
Returns
The Operators defining the ListOp
parameters
settings
Return settings.
Methods
add
add(other)
Return Operator addition of self and other, overloaded by +.
Parameters
other (OperatorBase) – An OperatorBase 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).
Returns
An OperatorBase equivalent to the sum of self and other.
Return type
adjoint
adjoint()
Return a new Operator equal to the Operator’s adjoint (conjugate transpose), overloaded by ~. For StateFns, this also turns the StateFn into a measurement.
Returns
An OperatorBase equivalent to the adjoint of self.
Return type
assign_parameters
assign_parameters(param_dict)
Binds scalar values to any Terra Parameters in the coefficients or primitives of the Operator, or substitutes one Parameter for another. This method differs from Terra’s assign_parameters in that it also supports lists of values to assign for a give Parameter, in which case self will be copied for each parameterization in the binding list(s), and all the copies will be returned in an OpList. If lists of parameterizations are used, every Parameter in the param_dict must have the same length list of parameterizations.
Parameters
param_dict (dict(opens in a new tab)) – The dictionary of Parameters to replace, and values or lists of values by which to replace them.
Returns
The OperatorBase with the Parameters in self replaced by the values or Parameters in param_dict. If param_dict contains parameterization lists, this OperatorBase is an OpList.
Return type
compose
compose(other, permutation=None, front=False)
Return Operator Composition between self and other (linear algebra-style: A@B(x) = A(B(x))), overloaded by @.
Note: You must be conscious of Quantum Circuit vs. Linear Algebra ordering conventions. Meaning, X.compose(Y) produces an X∘Y on qubit 0, but would produce a QuantumCircuit which looks like
-[Y]-[X]-
Because Terra prints circuits with the initial state at the left side of the circuit.
Parameters
- other (OperatorBase) – The
OperatorBasewith which to compose self. - permutation (List(opens in a new tab)[int(opens in a new tab)] | None) –
List[int]which defines permutation on other operator. - front (bool(opens in a new tab)) – If front==True, return
other.compose(self).
Returns
An OperatorBase equivalent to the function composition of self and other.
Return type
default_combo_fn
static default_combo_fn(x)
ListOp default combo function i.e. lambda x: x
Return type
equals
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.
Parameters
other (OperatorBase) – The OperatorBase to compare to self.
Returns
A bool equal to the equality of self and other.
Return type
eval
eval(front=None)
Evaluate the Operator’s underlying function, either on a binary string or another Operator. A square binary Operator can be defined as a function taking a binary function to another binary function. This method returns the value of that function for a given StateFn or binary string. For example, op.eval('0110').eval('1110') can be seen as querying the Operator’s matrix representation by row 6 and column 14, and will return the complex value at those “indices.” Similarly for a StateFn, op.eval('1011') will return the complex value at row 11 of the vector representation of the StateFn, as all StateFns are defined to be evaluated from Zero implicitly (i.e. it is as if .eval('0000') is already called implicitly to always “indexing” from column 0).
ListOp’s eval recursively evaluates each Operator in oplist, and combines the results using the recombination function combo_fn.
Parameters
front (str(opens in a new tab) |Dict(opens in a new tab)[str(opens in a new tab), complex(opens in a new tab)] | ndarray(opens in a new tab) |OperatorBase |Statevector | None) – The bitstring, dict of bitstrings (with values being coefficients), or StateFn to evaluated by the Operator’s underlying function.
Returns
The output of the oplist Operators’ evaluation function, combined with the combo_fn. If either self or front contain proper ListOps (not ListOp subclasses), the result is an n-dimensional list of complex or StateFn results, resulting from the recursive evaluation by each OperatorBase in the ListOps.
Raises
- NotImplementedError(opens in a new tab) – Raised if called for a subclass which is not distributive.
- TypeError(opens in a new tab) – Operators with mixed hierarchies, such as a ListOp containing both PrimitiveOps and ListOps, are not supported.
- NotImplementedError(opens in a new tab) – Attempting to call ListOp’s eval from a non-distributive subclass.
Return type
exp_i
exp_i()
Return an OperatorBase equivalent to an exponentiation of self * -i, e^(-i*op).
Return type
log_i
log_i(massive=False)
Return a MatrixOp equivalent to log(H)/-i for this operator H. This function is the effective inverse of exp_i, equivalent to finding the Hermitian Operator which produces self when exponentiated. For proper ListOps, applies log_i to all ops in oplist.
Return type
mul
mul(scalar)
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).
Parameters
scalar (complex(opens in a new tab) |ParameterExpression) – The real or complex scalar by which to multiply the Operator, or the ParameterExpression to serve as a placeholder for a scalar factor.
Returns
An OperatorBase equivalent to product of self and scalar.
Return type
permute
permute(permutation)
Permute the qubits of the operator.
Parameters
permutation (List(opens in a new tab)[int(opens in a new tab)]) – A list defining where each qubit should be permuted. The qubit at index j should be permuted to position permutation[j].
Returns
A new ListOp representing the permuted operator.
Raises
OpflowError – if indices do not define a new index for each qubit.
Return type
power
power(exponent)
Return Operator composed with self multiple times, overloaded by **.
Return type
primitive_strings
primitive_strings()
Return a set of strings describing the primitives contained in the Operator. For example, {'QuantumCircuit', 'Pauli'}. For hierarchical Operators, such as ListOps, this can help illuminate the primitives represented in the various recursive levels, and therefore which conversions can be applied.
Returns
A set of strings describing the primitives contained within the Operator.
Return type
reduce
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.
Returns
The reduced OperatorBase.
Return type
tensor
tensor(other)
Return tensor product between self and other, overloaded by ^. Note: You must be conscious of Qiskit’s big-endian bit printing convention. Meaning, X.tensor(Y) produces an X on qubit 0 and an Y on qubit 1, or X⨂Y, but would produce a QuantumCircuit which looks like
-[Y]- -[X]-
Because Terra prints circuits and results with qubit 0 at the end of the string or circuit.
Parameters
other (OperatorBase) – The OperatorBase to tensor product with self.
Returns
An OperatorBase equivalent to the tensor product of self and other.
Return type
tensorpower
tensorpower(other)
Return tensor product with self multiple times, overloaded by ^.
Parameters
other (int(opens in a new tab)) – The int number of times to tensor product self with itself via tensorpower.
Returns
An OperatorBase equivalent to the tensorpower of self by other.
Return type
to_circuit_op
to_circuit_op()
Returns an equivalent Operator composed of only QuantumCircuit-based primitives, such as CircuitOp and CircuitStateFn.
Return type
to_matrix
to_matrix(massive=False)
Return NumPy representation of the Operator. Represents the evaluation of the Operator’s underlying function on every combination of basis binary strings. Warn if more than 16 qubits to force having to set massive=True if such a large vector is desired.
Returns
The NumPy ndarray equivalent to this Operator.
Return type
to_matrix_op
to_matrix_op(massive=False)
Returns an equivalent Operator composed of only NumPy-based primitives, such as MatrixOp and VectorStateFn.
Return type
to_pauli_op
to_pauli_op(massive=False)
Returns an equivalent Operator composed of only Pauli-based primitives, such as PauliOp.
Return type
to_spmatrix
to_spmatrix()
Returns SciPy sparse matrix representation of the Operator.
Returns
CSR sparse matrix representation of the Operator, or List thereof.
Return type
spmatrix | List(opens in a new tab)[spmatrix]
traverse
traverse(convert_fn, coeff=None)
Apply the convert_fn to each node in the oplist.
Parameters
- convert_fn (Callable(opens in a new tab)) – The function to apply to the internal OperatorBase.
- coeff (complex(opens in a new tab) |ParameterExpression | None) – A coefficient to multiply by after applying convert_fn. If it is None, self.coeff is used instead.
Returns
The converted ListOp.
Return type