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ComposedOp

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

Bases: qiskit.opflow.list_ops.list_op.ListOp

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.

Parameters

  • oplist (List[OperatorBase]) – The Operators being composed.
  • coeff (Union[complex, ParameterExpression]) – A coefficient multiplying the operator
  • abelian (bool) – Indicates whether the Operators in oplist are known to mutually commute.

Methods Defined Here

adjoint

ComposedOp.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.

Return type

ComposedOp

Returns

An OperatorBase equivalent to the adjoint of self.

compose

ComposedOp.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 OperatorBase with which to compose self.
  • permutation (Optional[List[int]]) – List[int] which defines permutation on other operator.
  • front (bool) – If front==True, return other.compose(self).

Return type

OperatorBase

Returns

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

eval

ComposedOp.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 (Union[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.

Return type

Union[OperatorBase, complex]

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.

non_distributive_reduce

ComposedOp.non_distributive_reduce()

Reduce without attempting to expand all distributive compositions.

Return type

OperatorBase

Returns

The reduced Operator.

reduce

ComposedOp.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.

Return type

OperatorBase

Returns

The reduced OperatorBase.

to_circuit

ComposedOp.to_circuit()

Returns the quantum circuit, representing the composed operator.

Return type

QuantumCircuit

Returns

The circuit representation of the composed operator.

Raises

OpflowError – for operators where a single underlying circuit can not be obtained.

to_matrix

ComposedOp.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.

Return type

ndarray

Returns

The NumPy ndarray equivalent to this Operator.


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

Return type

bool

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

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