You are viewing the API reference for an old version of Qiskit. Switch to latest version

# OperatorBase

OperatorBaseGitHub(opens in a new tab)

Bases: qiskit.opflow.mixins.star_algebra.StarAlgebraMixin, qiskit.opflow.mixins.tensor.TensorMixin, abc.ABC

A base class for all Operators: PrimitiveOps, StateFns, ListOps, etc. Operators are defined as functions which take one complex binary function to another. These complex binary functions are represented by StateFns, which are themselves a special class of Operators taking only the Zero StateFn to the complex binary function they represent.

Operators can be used to construct complicated functions and computation, and serve as the building blocks for algorithms.

## Methods Defined Here

abstract OperatorBase.add(other)GitHub(opens in a new tab)

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).

Return type

OperatorBase

Returns

An OperatorBase equivalent to the sum of self and other.

abstract OperatorBase.adjoint()GitHub(opens in a new tab)

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

OperatorBase

Returns

An OperatorBase equivalent to the adjoint of self.

### assign_parameters

abstract OperatorBase.assign_parameters(param_dict)GitHub(opens in a new tab)

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[ParameterExpression, Union[complex, ParameterExpression, List[Union[complex, ParameterExpression]]]]) – The dictionary of Parameters to replace, and values or lists of values by which to replace them.

Return type

OperatorBase

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.

### bind_parameters

OperatorBase.bind_parameters(param_dict)GitHub(opens in a new tab)

Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters).

Return type

OperatorBase

### compose

abstract OperatorBase.compose(other, permutation=None, front=False)GitHub(opens in a new tab)

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.

### copy

OperatorBase.copy()GitHub(opens in a new tab)

Return a deep copy of the Operator.

Return type

OperatorBase

### equals

abstract OperatorBase.equals(other)GitHub(opens in a new tab)

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.

Return type

bool

Returns

A bool equal to the equality of self and other.

### eval

abstract OperatorBase.eval(front=None)GitHub(opens in a new tab)

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).

If front is None, the matrix-representation of the operator is returned.

Parameters

front (Union[str, Dict[str, complex], ndarray, OperatorBase, Statevector, None]) – The bitstring, dict of bitstrings (with values being coefficients), or StateFn to evaluated by the Operator’s underlying function, or None.

Return type

Union[OperatorBase, complex]

Returns

The output of the Operator’s evaluation function. If self is a StateFn, the result is a float or complex. If self is an Operator (PrimitiveOp, ComposedOp, SummedOp, EvolvedOp, etc.), the result is a StateFn. If front is None, the matrix-representation of the operator is returned, which is a MatrixOp for the operators and a VectorStateFn for state-functions. 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.

### is_hermitian

OperatorBase.is_hermitian()GitHub(opens in a new tab)

Return True if the operator is hermitian.

Returns: Boolean value

Return type

bool

### mul

abstract OperatorBase.mul(scalar)GitHub(opens in a new tab)

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 (Union[complex, ParameterExpression]) – The real or complex scalar by which to multiply the Operator, or the ParameterExpression to serve as a placeholder for a scalar factor.

Return type

OperatorBase

Returns

An OperatorBase equivalent to product of self and scalar.

### neg

OperatorBase.neg()GitHub(opens in a new tab)

Return the Operator’s negation, effectively just multiplying by -1.0, overloaded by -.

Return type

OperatorBase

Returns

An OperatorBase equivalent to the negation of self.

### permute

abstract OperatorBase.permute(permutation)GitHub(opens in a new tab)

Permutes the qubits of the operator.

Parameters

permutation (List[int]) – A list defining where each qubit should be permuted. The qubit at index j should be permuted to position permutation[j].

Return type

OperatorBase

Returns

A new OperatorBase containing the permuted operator.

Raises

OpflowError – if indices do not define a new index for each qubit.

### primitive_strings

abstract OperatorBase.primitive_strings()GitHub(opens in a new tab)

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.

Return type

Set[str]

Returns

A set of strings describing the primitives contained within the Operator.

### reduce

abstract OperatorBase.reduce()GitHub(opens in a new tab)

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.

### tensor

abstract OperatorBase.tensor(other)GitHub(opens in a new tab)

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.

Return type

OperatorBase

Returns

An OperatorBase equivalent to the tensor product of self and other.

### tensorpower

abstract OperatorBase.tensorpower(other)GitHub(opens in a new tab)

Return tensor product with self multiple times, overloaded by ^.

Parameters

other (int) – The int number of times to tensor product self with itself via tensorpower.

Return type

Union[OperatorBase, int]

Returns

An OperatorBase equivalent to the tensorpower of self by other.

### to_circuit_op

abstract OperatorBase.to_circuit_op()GitHub(opens in a new tab)

Returns a CircuitOp equivalent to this Operator.

Return type

OperatorBase

### to_matrix

abstract OperatorBase.to_matrix(massive=False)GitHub(opens in a new tab)

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.

### to_matrix_op

abstract OperatorBase.to_matrix_op(massive=False)GitHub(opens in a new tab)

Returns a MatrixOp equivalent to this Operator.

Return type

OperatorBase

### to_spmatrix

OperatorBase.to_spmatrix()GitHub(opens in a new tab)

Return SciPy sparse matrix representation of the Operator. Represents the evaluation of the Operator’s underlying function on every combination of basis binary strings.

Return type

spmatrix

Returns

The SciPy spmatrix equivalent to this Operator.

## Attributes

= '  '

### instance_id

Return the unique instance id.

Return type

int

### num_qubits

The number of qubits over which the Operator is defined. If op.num_qubits == 5, then op.eval('1' * 5) will be valid, but op.eval('11') will not.

Return type

int

Returns

The number of qubits accepted by the Operator’s underlying function.

### parameters

Return a set of Parameter objects contained in the Operator.

### settings

Return settings of this object in a dictionary.

You can, for example, use this settings dictionary to serialize the object in JSON format, if the JSON encoder you use supports all types in the dictionary.

Return type

Dict

Returns

Object settings in a dictionary.