text: # This code is part of Qiskit.
  #
  # (C) Copyright IBM 2017.
  #
  # 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.
  
  """Identity gate."""
  
  import numpy
  from qiskit.circuit.gate import Gate
  
  
  class IGate(Gate):
      r"""Identity gate.
  
      Identity gate corresponds to a single-qubit gate wait cycle,
      and should not be optimized or unrolled (it is an opaque gate).
  
      **Matrix Representation:**
  
      .. math::
  
          I = \begin{pmatrix}
                  1 & 0 \\
                  0 & 1
              \end{pmatrix}
  
      **Circuit symbol:**
  
      .. parsed-literal::
               ┌───┐
          q_0: ┤ I ├
               └───┘
      """
  
      def __init__(self, label=None):
          """Create new Identity gate."""
          super().__init__("id", 1, [], label=label)
  
      def inverse(self):
          """Invert this gate."""
          return IGate()  # self-inverse
  
      def __array__(self, dtype=None):
          """Return a numpy.array for the identity gate."""
          return numpy.array([[1, 0], [0, 1]], dtype=dtype)
  