code: def _matrix_M_entry(row, col):
      """Returns one entry for the matrix that maps alpha to theta.
  
      See Eq. (3) in `Möttönen et al. (2004) <https://arxiv.org/abs/quant-ph/0407010>`_.
  
      Args:
          row (int): one-based row number
          col (int): one-based column number
  
      Returns:
          (float): transformation matrix entry at given row and column
      """
      # (col >> 1) ^ col is the Gray code of col
      b_and_g = row & ((col >> 1) ^ col)
      sum_of_ones = 0
      while b_and_g > 0:
          if b_and_g & 0b1:
              sum_of_ones += 1
  
          b_and_g = b_and_g >> 1
  
      return (-1) ** sum_of_ones
  
file_path: pennylane/pennylane/templates/state_preparations/mottonen.py
imports: import numpy
  import pennylane
  from pennylane.operation import Operation, AnyWires
label_desc: Use image node_id 2 for calling a global function with example usage: _matrix_M_entry(row, col) and returns: unknown