code: def to_positions(self):
          
          if self.coords_are_displacement:
              cumulative_displacements = np.cumsum(self.frac_coords, axis=0)
              positions = self.base_positions + cumulative_displacements
              self.frac_coords = positions
              self.coords_are_displacement = False
          return
docs: Converts fractional coordinates of trajectory into positions