ComposedOp
class qiskit.opflow.list_ops.ComposedOp(oplist, coeff=1.0, abelian=False)
Bases: ListOp
Deprecated: A class for lazily representing compositions of Operators. Often Operators cannot be efficiently composed with one another, but may be manipulated further so that they can be composed later. This class holds logic to indicate that the Operators in oplist are meant to be composed, and therefore if they reach a point in which they can be, such as after conversion to QuantumCircuits or matrices, they can be reduced by composition.
The class qiskit.opflow.list_ops.composed_op.ComposedOp is deprecated as of qiskit-terra 0.24.0. It will be removed no earlier than 3 months after the release date. For code migration guidelines, visit https://qisk.it/opflow_migration.
Parameters
- oplist (List[OperatorBase]) – The Operators being composed.
- coeff (complex |ParameterExpression) – A coefficient multiplying the operator
- abelian (bool) – Indicates whether the Operators in
oplistare known to mutually commute.
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
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
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
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[int] | None) –
List[int]which defines permutation on other operator. - front (bool) – If front==True, return
other.compose(self).
Returns
An OperatorBase equivalent to the function composition 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 |dict |ndarray |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 – Raised if called for a subclass which is not distributive.
- TypeError – Operators with mixed hierarchies, such as a ListOp containing both PrimitiveOps and ListOps, are not supported.
- NotImplementedError – Attempting to call ListOp’s eval from a non-distributive subclass.
Return type
non_distributive_reduce
non_distributive_reduce()
Reduce without attempting to expand all distributive compositions.
Returns
The reduced 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
to_circuit
to_circuit()
Returns the quantum circuit, representing the composed operator.
Returns
The circuit representation of the composed operator.
Raises
OpflowError – for operators where a single underlying circuit can not be obtained.
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