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---
title: ScalarOp
description: API reference for qiskit.quantum_info.ScalarOp
in_page_toc_min_heading_level: 1
python_api_type: class
python_api_name: qiskit.quantum_info.ScalarOp
---
# qiskit.quantum\_info.ScalarOp
<Class id="qiskit.quantum_info.ScalarOp" isDedicatedPage={true} github="https://github.com/qiskit/qiskit/tree/stable/0.17/qiskit/quantum_info/operators/scalar_op.py" signature="ScalarOp(dims=None, coeff=1)" modifiers="class">
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()`](#qiskit.quantum_info.ScalarOp.compose "qiskit.quantum_info.ScalarOp.compose"), [`dot()`](#qiskit.quantum_info.ScalarOp.dot "qiskit.quantum_info.ScalarOp.dot"), [`tensor()`](#qiskit.quantum_info.ScalarOp.tensor "qiskit.quantum_info.ScalarOp.tensor"), [`expand()`](#qiskit.quantum_info.ScalarOp.expand "qiskit.quantum_info.ScalarOp.expand") methods.
Initialize an operator object.
**Parameters**
* **dims** (*int or tuple*) – subsystem dimensions.
* **coeff** (*Number*) – scalar coefficient for the identity operator (Default: 1).
**Raises**
**QiskitError** – If the optional coefficient is invalid.
### \_\_init\_\_
<Function id="qiskit.quantum_info.ScalarOp.__init__" signature="__init__(dims=None, coeff=1)">
Initialize an operator object.
**Parameters**
* **dims** (*int or tuple*) – subsystem dimensions.
* **coeff** (*Number*) – scalar coefficient for the identity operator (Default: 1).
**Raises**
**QiskitError** – If the optional coefficient is invalid.
</Function>
## Methods
| | |
| ------------------------------------------------------------------------------------------------------------------------------------ | -------------------------------------------------------------------------- |
| [`__init__`](#qiskit.quantum_info.ScalarOp.__init__ "qiskit.quantum_info.ScalarOp.__init__")(\[dims, coeff]) | Initialize an operator object. |
| [`adjoint`](#qiskit.quantum_info.ScalarOp.adjoint "qiskit.quantum_info.ScalarOp.adjoint")() | Return the adjoint of the Operator. |
| [`compose`](#qiskit.quantum_info.ScalarOp.compose "qiskit.quantum_info.ScalarOp.compose")(other\[, qargs, front]) | Return the operator composition with another ScalarOp. |
| [`conjugate`](#qiskit.quantum_info.ScalarOp.conjugate "qiskit.quantum_info.ScalarOp.conjugate")() | Return the conjugate of the ScalarOp. |
| [`copy`](#qiskit.quantum_info.ScalarOp.copy "qiskit.quantum_info.ScalarOp.copy")() | Make a deep copy of current operator. |
| [`dot`](#qiskit.quantum_info.ScalarOp.dot "qiskit.quantum_info.ScalarOp.dot")(other\[, qargs]) | Return the right multiplied operator self \* other. |
| [`expand`](#qiskit.quantum_info.ScalarOp.expand "qiskit.quantum_info.ScalarOp.expand")(other) | Return the reverse-order tensor product with another ScalarOp. |
| [`input_dims`](#qiskit.quantum_info.ScalarOp.input_dims "qiskit.quantum_info.ScalarOp.input_dims")(\[qargs]) | Return tuple of input dimension for specified subsystems. |
| [`is_unitary`](#qiskit.quantum_info.ScalarOp.is_unitary "qiskit.quantum_info.ScalarOp.is_unitary")(\[atol, rtol]) | Return True if operator is a unitary matrix. |
| [`output_dims`](#qiskit.quantum_info.ScalarOp.output_dims "qiskit.quantum_info.ScalarOp.output_dims")(\[qargs]) | Return tuple of output dimension for specified subsystems. |
| [`power`](#qiskit.quantum_info.ScalarOp.power "qiskit.quantum_info.ScalarOp.power")(n) | Return the power of the ScalarOp. |
| [`reshape`](#qiskit.quantum_info.ScalarOp.reshape "qiskit.quantum_info.ScalarOp.reshape")(\[input\_dims, output\_dims, num\_qubits]) | Return a shallow copy with reshaped input and output subsystem dimensions. |
| [`tensor`](#qiskit.quantum_info.ScalarOp.tensor "qiskit.quantum_info.ScalarOp.tensor")(other) | Return the tensor product with another ScalarOp. |
| [`to_matrix`](#qiskit.quantum_info.ScalarOp.to_matrix "qiskit.quantum_info.ScalarOp.to_matrix")() | Convert to a Numpy matrix. |
| [`to_operator`](#qiskit.quantum_info.ScalarOp.to_operator "qiskit.quantum_info.ScalarOp.to_operator")() | Convert to an Operator object. |
| [`transpose`](#qiskit.quantum_info.ScalarOp.transpose "qiskit.quantum_info.ScalarOp.transpose")() | Return the transpose of the ScalarOp. |
## Attributes
| | |
| -------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------- |
| [`atol`](#qiskit.quantum_info.ScalarOp.atol "qiskit.quantum_info.ScalarOp.atol") | Default absolute tolerance parameter for float comparisons. |
| [`coeff`](#qiskit.quantum_info.ScalarOp.coeff "qiskit.quantum_info.ScalarOp.coeff") | Return the coefficient |
| [`dim`](#qiskit.quantum_info.ScalarOp.dim "qiskit.quantum_info.ScalarOp.dim") | Return tuple (input\_shape, output\_shape). |
| [`num_qubits`](#qiskit.quantum_info.ScalarOp.num_qubits "qiskit.quantum_info.ScalarOp.num_qubits") | Return the number of qubits if a N-qubit operator or None otherwise. |
| [`qargs`](#qiskit.quantum_info.ScalarOp.qargs "qiskit.quantum_info.ScalarOp.qargs") | Return the qargs for the operator. |
| [`rtol`](#qiskit.quantum_info.ScalarOp.rtol "qiskit.quantum_info.ScalarOp.rtol") | Default relative tolerance parameter for float comparisons. |
### adjoint
<Function id="qiskit.quantum_info.ScalarOp.adjoint" signature="adjoint()">
Return the adjoint of the Operator.
</Function>
### atol
<Attribute id="qiskit.quantum_info.ScalarOp.atol">
Default absolute tolerance parameter for float comparisons.
</Attribute>
### coeff
<Attribute id="qiskit.quantum_info.ScalarOp.coeff">
Return the coefficient
</Attribute>
### compose
<Function id="qiskit.quantum_info.ScalarOp.compose" signature="compose(other, qargs=None, front=False)">
Return the operator composition with another ScalarOp.
**Parameters**
* **other** ([*ScalarOp*](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.ScalarOp")) – a ScalarOp object.
* **qargs** (*list or None*) – Optional, a list of subsystem positions to apply other on. If None apply on all subsystems (default: None).
* **front** (*bool*) – If True compose using right operator multiplication, instead of left multiplication \[default: False].
**Returns**
The composed ScalarOp.
**Return type**
[ScalarOp](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.ScalarOp")
**Raises**
**QiskitError** – if other cannot be converted to an operator, or has incompatible dimensions for specified subsystems.
<Admonition title="Note" type="note">
Composition (`&`) by default is defined as left matrix multiplication for matrix operators, while [`dot()`](#qiskit.quantum_info.ScalarOp.dot "qiskit.quantum_info.ScalarOp.dot") is defined as right matrix multiplication. That is that `A & B == A.compose(B)` is equivalent to `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()`](#qiskit.quantum_info.ScalarOp.dot "qiskit.quantum_info.ScalarOp.dot") method `A.dot(B) == A.compose(B, front=True)`.
</Admonition>
</Function>
### conjugate
<Function id="qiskit.quantum_info.ScalarOp.conjugate" signature="conjugate()">
Return the conjugate of the ScalarOp.
</Function>
### copy
<Function id="qiskit.quantum_info.ScalarOp.copy" signature="copy()">
Make a deep copy of current operator.
</Function>
### dim
<Attribute id="qiskit.quantum_info.ScalarOp.dim">
Return tuple (input\_shape, output\_shape).
</Attribute>
### dot
<Function id="qiskit.quantum_info.ScalarOp.dot" signature="dot(other, qargs=None)">
Return the right multiplied operator self \* other.
**Parameters**
* **other** ([*Operator*](qiskit.quantum_info.Operator "qiskit.quantum_info.Operator")) – an operator object.
* **qargs** (*list 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](qiskit.quantum_info.Operator "qiskit.quantum_info.Operator")
</Function>
### expand
<Function id="qiskit.quantum_info.ScalarOp.expand" signature="expand(other)">
Return the reverse-order tensor product with another ScalarOp.
**Parameters**
**other** ([*ScalarOp*](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.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](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.ScalarOp")
</Function>
### input\_dims
<Function id="qiskit.quantum_info.ScalarOp.input_dims" signature="input_dims(qargs=None)">
Return tuple of input dimension for specified subsystems.
</Function>
### is\_unitary
<Function id="qiskit.quantum_info.ScalarOp.is_unitary" signature="is_unitary(atol=None, rtol=None)">
Return True if operator is a unitary matrix.
</Function>
### num\_qubits
<Attribute id="qiskit.quantum_info.ScalarOp.num_qubits">
Return the number of qubits if a N-qubit operator or None otherwise.
</Attribute>
### output\_dims
<Function id="qiskit.quantum_info.ScalarOp.output_dims" signature="output_dims(qargs=None)">
Return tuple of output dimension for specified subsystems.
</Function>
### power
<Function id="qiskit.quantum_info.ScalarOp.power" signature="power(n)">
Return the power of the ScalarOp.
**Parameters**
**n** (*float*) – the exponent for the scalar op.
**Returns**
the `coeff ** n` ScalarOp.
**Return type**
[ScalarOp](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.ScalarOp")
</Function>
### qargs
<Attribute id="qiskit.quantum_info.ScalarOp.qargs">
Return the qargs for the operator.
</Attribute>
### reshape
<Function id="qiskit.quantum_info.ScalarOp.reshape" signature="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*) – new subsystem input dimensions. If None the original input dims will be preserved \[Default: None].
* **output\_dims** (*None or tuple*) – new subsystem output dimensions. If None the original output dims will be preserved \[Default: None].
* **num\_qubits** (*None or int*) – 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.
</Function>
### rtol
<Attribute id="qiskit.quantum_info.ScalarOp.rtol">
Default relative tolerance parameter for float comparisons.
</Attribute>
### tensor
<Function id="qiskit.quantum_info.ScalarOp.tensor" signature="tensor(other)">
Return the tensor product with another ScalarOp.
**Parameters**
**other** ([*ScalarOp*](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.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](#qiskit.quantum_info.ScalarOp "qiskit.quantum_info.ScalarOp")
<Admonition title="Note" type="note">
The tensor product can be obtained using the `^` binary operator. Hence `a.tensor(b)` is equivalent to `a ^ b`.
</Admonition>
</Function>
### to\_matrix
<Function id="qiskit.quantum_info.ScalarOp.to_matrix" signature="to_matrix()">
Convert to a Numpy matrix.
</Function>
### to\_operator
<Function id="qiskit.quantum_info.ScalarOp.to_operator" signature="to_operator()">
Convert to an Operator object.
</Function>
### transpose
<Function id="qiskit.quantum_info.ScalarOp.transpose" signature="transpose()">
Return the transpose of the ScalarOp.
</Function>
</Class>
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