OperatorBase
class OperatorBase
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 in Aqua.
Attributes
num_qubits
abstract property
Type: int
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.
Methods
__mul__
OperatorBase.__mul__(other)
Overload * for Operator scalar multiplication.
Parameters
other (Number) – 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
Returns
An OperatorBase equivalent to product of self and scalar.
add
abstract OperatorBase.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).
Return type
Returns
An OperatorBase equivalent to the sum of self and other.
adjoint
abstract OperatorBase.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
Returns
An OperatorBase equivalent to the adjoint of self.
assign_parameters
abstract OperatorBase.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[ParameterExpression, Union[Number, ParameterExpression, List[Union[Number, ParameterExpression]]]]) – The dictionary of Parameters to replace, and values or lists of values by which to replace them.
Return type
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)
Same as assign_parameters, but maintained for consistency with QuantumCircuit in Terra (which has both assign_parameters and bind_parameters).
Return type
compose
abstract OperatorBase.compose(other)
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.
Return type
Returns
An OperatorBase equivalent to the function composition of self and other.
equals
abstract OperatorBase.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.
Return type
bool
Returns
A bool equal to the equality of self and other.
eval
abstract OperatorBase.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).
Parameters
front (Union[str, Dict[str, complex], OperatorBase, None]) – The bitstring, dict of bitstrings (with values being coefficients), or StateFn to evaluated by the Operator’s underlying function.
Return type
Union[OperatorBase, float, complex, list]
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 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.
mul
abstract OperatorBase.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 (Union[Number, 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
Returns
An OperatorBase equivalent to product of self and scalar.
neg
OperatorBase.neg()
Return the Operator’s negation, effectively just multiplying by -1.0, overloaded by -.
Return type
Returns
An OperatorBase equivalent to the negation of self.
power
abstract OperatorBase.power(exponent)
Return Operator composed with self multiple times, overloaded by **.
Parameters
exponent (int) – The int number of times to compose self with itself.
Return type
Returns
An OperatorBase equivalent to self composed with itself exponent times.
primitive_strings
abstract OperatorBase.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.
Return type
Set[str]
Returns
A set of strings describing the primitives contained within the Operator.
reduce
abstract OperatorBase.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.
tensor
abstract OperatorBase.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.
Return type
Returns
An OperatorBase equivalent to the tensor product of self and other.
tensorpower
abstract OperatorBase.tensorpower(other)
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
Returns
An OperatorBase equivalent to the tensorpower of self by other.
to_legacy_op
abstract OperatorBase.to_legacy_op(massive=False)
Attempt to return the Legacy Operator representation of the Operator. If self is a SummedOp of PauliOps, will attempt to convert to WeightedPauliOperator, and otherwise will simply convert to MatrixOp and then to MatrixOperator. The Legacy Operators cannot represent StateFns or proper ListOps (meaning not one of the ListOp subclasses), so an error will be thrown if this method is called on such an Operator. Also, Legacy Operators cannot represent unbound Parameter coeffs, so an error will be thrown if any are present in self.
Warn if more than 16 qubits to force having to set massive=True if such a large vector is desired.
Return type
Returns
The LegacyBaseOperator representing this Operator.
Raises
TypeError – self is an Operator which cannot be represented by a LegacyBaseOperator, such as StateFn, proper (non-subclass) ListOp, or an Operator with an unbound coeff Parameter.
to_matrix
abstract OperatorBase.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.