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ComposedOp

qiskit.opflow.list_ops.ComposedOp(oplist, coeff=1.0, abelian=False) GitHub(opens in a new tab)

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.

Deprecated since version 0.24.0

The class qiskit.opflow.list_ops.composed_op.ComposedOp 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


Attributes

INDENTATION

= '  '

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

ComposedOp

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

Returns

An OperatorBase equivalent to the function composition of self and other.

Return type

OperatorBase

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) |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

Return type

OperatorBase | complex(opens in a new tab)

non_distributive_reduce

non_distributive_reduce()

Reduce without attempting to expand all distributive compositions.

Returns

The reduced Operator.

Return type

OperatorBase

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

OperatorBase

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

QuantumCircuit

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

ndarray(opens in a new tab)

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