code: def update_positions(self, time, xs, ys, zs, vxs, vys, vzs,
                           ethetas, elongans, eincls,
                           ds=None, Fs=None, ignore_effects=False):
          
          self.xs = np.array(_value(xs))
          self.ys = np.array(_value(ys))
          self.zs = np.array(_value(zs))
  
          for starref,body in self.items():
              body.update_position(time, xs, ys, zs, vxs, vys, vzs,
                                   ethetas, elongans, eincls,
                                   ds=ds, Fs=Fs, ignore_effects=ignore_effects)
docs: TODO: add documentation
  
          all arrays should be for the current time, but iterable over all bodies