# ScalarOp

qiskit.quantum_info.ScalarOp(dims=None, coeff=1)

Bases: LinearOp

Scalar identity operator class.

This is a symbolic representation of an scalar identity operator on multiple subsystems. It may be used to initialize a symbolic scalar multiplication of an identity and then be implicitly converted to other kinds of operator subclasses by using the compose(), dot(), tensor(), expand() methods.

Initialize an operator object.

Parameters

Raises

QiskitError – If the optional coefficient is invalid.

## Attributes

### atol

= 1e-08

### coeff

Return the coefficient

### dim

Return tuple (input_shape, output_shape).

### num_qubits

Return the number of qubits if a N-qubit operator or None otherwise.

### qargs

Return the qargs for the operator.

### rtol

= 1e-05

## Methods

adjoint()

Return the adjoint of the Operator.

Return type

Self

### compose

compose(other, qargs=None, front=False)

Return the operator composition with another ScalarOp.

Parameters

• other (ScalarOp) – a ScalarOp object.
• qargs (list (opens in a new tab) or None) – Optional, a list of subsystem positions to apply other on. If None apply on all subsystems (default: None).
• front (bool (opens in a new tab)) – If True compose using right operator multiplication, instead of left multiplication [default: False].

Returns

The composed ScalarOp.

Return type

ScalarOp

Raises

QiskitError – if other cannot be converted to an operator, or has incompatible dimensions for specified subsystems.

Note

Composition (&) by default is defined as left matrix multiplication for matrix operators, while @ (equivalent to dot()) is defined as right matrix multiplication. That is that A & B == A.compose(B) is equivalent to B @ A == B.dot(A) when A and B are of the same type.

Setting the front=True kwarg changes this to right matrix multiplication and is equivalent to the dot() method A.dot(B) == A.compose(B, front=True).

### conjugate

conjugate()

Return the conjugate of the ScalarOp.

### copy

copy()

Make a deep copy of current operator.

### dot

dot(other, qargs=None)

Return the right multiplied operator self * other.

Parameters

• other (Operator) – an operator object.
• qargs (list (opens in a new tab) or None) – Optional, a list of subsystem positions to apply other on. If None apply on all subsystems (default: None).

Returns

The right matrix multiplied Operator.

Return type

Operator

Note

The dot product can be obtained using the @ binary operator. Hence a.dot(b) is equivalent to a @ b.

### expand

expand(other)

Return the reverse-order tensor product with another ScalarOp.

Parameters

other (ScalarOp) – a ScalarOp object.

Returns

the tensor product $b \otimes a$, where $a$

is the current ScalarOp, and $b$ is the other ScalarOp.

Return type

ScalarOp

### input_dims

input_dims(qargs=None)

Return tuple of input dimension for specified subsystems.

### is_unitary

is_unitary(atol=None, rtol=None)

Return True if operator is a unitary matrix.

### output_dims

output_dims(qargs=None)

Return tuple of output dimension for specified subsystems.

### power

power(n)

Return the power of the ScalarOp.

Parameters

n (float (opens in a new tab)) – the exponent for the scalar op.

Returns

the coeff ** n ScalarOp.

Return type

ScalarOp

### reshape

reshape(input_dims=None, output_dims=None, num_qubits=None)

Return a shallow copy with reshaped input and output subsystem dimensions.

Parameters

• input_dims (None or tuple (opens in a new tab)) – new subsystem input dimensions. If None the original input dims will be preserved [Default: None].
• output_dims (None or tuple (opens in a new tab)) – new subsystem output dimensions. If None the original output dims will be preserved [Default: None].
• num_qubits (None or int (opens in a new tab)) – reshape to an N-qubit operator [Default: None].

Returns

returns self with reshaped input and output dimensions.

Return type

BaseOperator

Raises

QiskitError – if combined size of all subsystem input dimension or subsystem output dimensions is not constant.

### tensor

tensor(other)

Return the tensor product with another ScalarOp.

Parameters

other (ScalarOp) – a ScalarOp object.

Returns

the tensor product $a \otimes b$, where $a$

is the current ScalarOp, and $b$ is the other ScalarOp.

Return type

ScalarOp

Note

The tensor product can be obtained using the ^ binary operator. Hence a.tensor(b) is equivalent to a ^ b.

### to_matrix

to_matrix()

Convert to a Numpy matrix.

### to_operator

to_operator()

Convert to an Operator object.

Return type

Operator

### transpose

transpose()

Return the transpose of the ScalarOp.