# Source code for qiskit.providers.aer.library.set_instructions.set_unitary

```
# This code is part of Qiskit.
#
# (C) Copyright IBM 2018, 2021.
#
# This code is licensed under the Apache License, Version 2.0. You may
# obtain a copy of this license in the LICENSE.txt file in the root directory
# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
#
# Any modifications or derivative works of this code must retain this
# copyright notice, and modified files need to carry a notice indicating
# that they have been altered from the originals.
"""
Instruction to set the state simulator state to a matrix.
"""
from qiskit.circuit import QuantumCircuit, Instruction
from qiskit.extensions.exceptions import ExtensionError
from qiskit.quantum_info import Operator
from ..default_qubits import default_qubits
[docs]class SetUnitary(Instruction):
"""Set unitary state of the simulator"""
_directive = True
[docs] def __init__(self, state):
"""Create new instruction to set the unitary simulator state.
Args:
state (Operator): A unitary matrix.
Raises:
ExtensionError: if the input matrix is not state.
.. note::
This set instruction must always be performed on the full width of
qubits in a circuit, otherwise an exception will be raised during
simulation.
"""
if not isinstance(state, Operator):
state = Operator(state)
if not state.num_qubits or not state.is_unitary():
raise ExtensionError("The input matrix is not unitary")
super().__init__('set_unitary', state.num_qubits, 0,
[state.data])
[docs]def set_unitary(self, state):
"""Set the state state of the simulator.
Args:
state (Operator): A state matrix.
Returns:
QuantumCircuit: with attached instruction.
Raises:
ExtensionError: If the state is the incorrect size for the
current circuit.
ExtensionError: if the input matrix is not unitary.
.. note:
This instruction is always defined across all qubits in a circuit.
"""
qubits = default_qubits(self)
if not isinstance(state, Operator):
state = Operator(state)
if not state.num_qubits or state.num_qubits != len(qubits):
raise ExtensionError(
"The size of the unitary matrix for the set_unitary"
" instruction must be equal to the number of qubits"
f" in the circuit (state.num_qubits ({state.num_qubits})"
f" != QuantumCircuit.num_qubits ({self.num_qubits})).")
return self.append(SetUnitary(state), qubits)
QuantumCircuit.set_unitary = set_unitary
```