code: def to_displacements(self):
          
          if not self.coords_are_displacement:
              displacements = np.subtract(self.frac_coords, np.roll(self.frac_coords, 1, axis=0))
              displacements[0] = np.zeros(np.shape(self.frac_coords[0]))
              # Deal with PBC
              displacements = [np.subtract(item, np.round(item)) for item in displacements]
  
              self.frac_coords = displacements
              self.coords_are_displacement = True
          return
docs: Converts position coordinates of trajectory into displacements between consecutive frames