docs: def phase_transformation(Ne, Nl, r, Lij, omega_laser, phase):
      r"""Obtain a phase transformation to eliminate explicit time dependence.
  
      >>> Ne = 2
  
      """
      ph = find_phase_transformation(Ne, Nl, r, Lij)
  
      return {phase[i]: sum([ph[i][j]*omega_laser[j] for j in range(Nl)])
              for i in range(Ne)}