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# Code source de qiskit.circuit.gate

```# This code is part of Qiskit.
#
#
# obtain a copy of this license in the LICENSE.txt file in the root directory
#
# 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.

"""Unitary gate."""

from typing import List, Optional, Union, Tuple
import numpy as np

from qiskit.circuit.parameterexpression import ParameterExpression
from qiskit.circuit.exceptions import CircuitError
from .instruction import Instruction

[docs]class Gate(Instruction):
"""Unitary gate."""

def __init__(
self, name: str, num_qubits: int, params: List, label: Optional[str] = None
) -> None:
"""Create a new gate.

Args:
name: The Qobj name of the gate.
num_qubits: The number of qubits the gate acts on.
params: A list of parameters.
label: An optional label for the gate.
"""
self.definition = None
super().__init__(name, num_qubits, 0, params, label=label)

# Set higher priority than Numpy array and matrix classes
__array_priority__ = 20

[docs]    def to_matrix(self) -> np.ndarray:
"""Return a Numpy.array for the gate unitary matrix.

Returns:
np.ndarray: if the Gate subclass has a matrix definition.

Raises:
CircuitError: If a Gate subclass does not implement this method an
exception will be raised when this base class method is called.
"""
if hasattr(self, "__array__"):
# pylint: disable=no-member
return self.__array__(dtype=complex)
raise CircuitError(f"to_matrix not defined for this {type(self)}")

[docs]    def power(self, exponent: float):
"""Creates a unitary gate as `gate^exponent`.

Args:
exponent (float): Gate^exponent

Returns:
qiskit.extensions.UnitaryGate: To which `to_matrix` is self.to_matrix^exponent.

Raises:
CircuitError: If Gate is not unitary
"""
from qiskit.quantum_info.operators import Operator  # pylint: disable=cyclic-import
from qiskit.extensions.unitary import UnitaryGate  # pylint: disable=cyclic-import
from scipy.linalg import schur

# Should be diagonalized because it's a unitary.
decomposition, unitary = schur(Operator(self).data, output="complex")
# Raise the diagonal entries to the specified power
decomposition_power = []

decomposition_diagonal = decomposition.diagonal()
# assert off-diagonal are 0
if not np.allclose(np.diag(decomposition_diagonal), decomposition):
raise CircuitError("The matrix is not diagonal")

for element in decomposition_diagonal:
decomposition_power.append(pow(element, exponent))
# Then reconstruct the resulting gate.
unitary_power = unitary @ np.diag(decomposition_power) @ unitary.conj().T
return UnitaryGate(unitary_power, label=f"{self.name}^{exponent}")

def __pow__(self, exponent: float) -> "Gate":
return self.power(exponent)

def _return_repeat(self, exponent: float) -> "Gate":
return Gate(name=f"{self.name}*{exponent}", num_qubits=self.num_qubits, params=self.params)

[docs]    def control(
self,
num_ctrl_qubits: int = 1,
label: Optional[str] = None,
ctrl_state: Optional[Union[int, str]] = None,
):
"""Return controlled version of gate. See :class:`.ControlledGate` for usage.

Args:
num_ctrl_qubits: number of controls to add to gate (default=1)
label: optional gate label
ctrl_state: The control state in decimal or as a bitstring
(e.g. '111'). If None, use 2**num_ctrl_qubits-1.

Returns:
qiskit.circuit.ControlledGate: Controlled version of gate. This default algorithm
uses num_ctrl_qubits-1 ancillae qubits so returns a gate of size
num_qubits + 2*num_ctrl_qubits - 1.

Raises:
QiskitError: unrecognized mode or invalid ctrl_state
"""
# pylint: disable=cyclic-import

@staticmethod
"""Expands a single argument.

For example: [q[0], q[1]] -> [q[0]], [q[1]]
"""
# [q[0], q[1]] -> [q[0]]
#              -> [q[1]]
for arg0 in qarg:
yield [arg0], []

@staticmethod
def _broadcast_2_arguments(qarg0: List, qarg1: List) -> List:
if len(qarg0) == len(qarg1):
# [[q[0], q[1]], [r[0], r[1]]] -> [q[0], r[0]]
#                              -> [q[1], r[1]]
for arg0, arg1 in zip(qarg0, qarg1):
yield [arg0, arg1], []
elif len(qarg0) == 1:
# [[q[0]], [r[0], r[1]]] -> [q[0], r[0]]
#                        -> [q[0], r[1]]
for arg1 in qarg1:
yield [qarg0[0], arg1], []
elif len(qarg1) == 1:
# [[q[0], q[1]], [r[0]]] -> [q[0], r[0]]
#                        -> [q[1], r[0]]
for arg0 in qarg0:
yield [arg0, qarg1[0]], []
else:
raise CircuitError(
f"Not sure how to combine these two-qubit arguments:\n {qarg0}\n {qarg1}"
)

@staticmethod
if all(len(qarg) == len(qargs[0]) for qarg in qargs):
for arg in zip(*qargs):
yield list(arg), []
else:
raise CircuitError("Not sure how to combine these qubit arguments:\n %s\n" % qargs)

[docs]    def broadcast_arguments(self, qargs: List, cargs: List) -> Tuple[List, List]:
"""Validation and handling of the arguments and its relationship.

For example, ``cx([q[0],q[1]], q[2])`` means ``cx(q[0], q[2]); cx(q[1], q[2])``. This
method yields the arguments in the right grouping. In the given example::

in: [[q[0],q[1]], q[2]],[]
outs: [q[0], q[2]], []
[q[1], q[2]], []

* If len(qargs) == 1::

[q[0], q[1]] -> [q[0]],[q[1]]

* If len(qargs) == 2::

[[q[0], q[1]], [r[0], r[1]]] -> [q[0], r[0]], [q[1], r[1]]
[[q[0]], [r[0], r[1]]]       -> [q[0], r[0]], [q[0], r[1]]
[[q[0], q[1]], [r[0]]]       -> [q[0], r[0]], [q[1], r[0]]

* If len(qargs) >= 3::

[q[0], q[1]], [r[0], r[1]],  ...] -> [q[0], r[0], ...], [q[1], r[1], ...]

Args:
qargs: List of quantum bit arguments.
cargs: List of classical bit arguments.

Returns:
A tuple with single arguments.

Raises:
CircuitError: If the input is not valid. For example, the number of
arguments does not match the gate expectation.
"""
if len(qargs) != self.num_qubits or cargs:
raise CircuitError(
f"The amount of qubit({len(qargs)})/clbit({len(cargs)}) arguments does"
f" not match the gate expectation ({self.num_qubits})."
)

if any(not qarg for qarg in qargs):
raise CircuitError("One or more of the arguments are empty")

if len(qargs) == 0:
return [
([], []),
]
if len(qargs) == 1:
elif len(qargs) == 2:
elif len(qargs) >= 3:
else:
raise CircuitError("This gate cannot handle %i arguments" % len(qargs))

[docs]    def validate_parameter(self, parameter):
"""Gate parameters should be int, float, or ParameterExpression"""
if isinstance(parameter, ParameterExpression):
if len(parameter.parameters) > 0:
return parameter  # expression has free parameters, we cannot validate it
if not parameter.is_real():
msg = f"Bound parameter expression is complex in gate {self.name}"
raise CircuitError(msg)
return parameter  # per default assume parameters must be real when bound
if isinstance(parameter, (int, float)):
return parameter
elif isinstance(parameter, (np.integer, np.floating)):
return parameter.item()
else:
raise CircuitError(f"Invalid param type {type(parameter)} for gate {self.name}.")
```