code: def _read_frame(self):
          
          pos = np.zeros((self.num_atoms, 3), float)
          vel = np.zeros((self.num_atoms, 3), float)
          for i in range(self.num_atoms):
              line = next(self._f)
              words = line.split()
              pos[i, 0] = float(words[1])
              pos[i, 1] = float(words[2])
              pos[i, 2] = float(words[3])
              vel[i, 0] = float(words[4])
              vel[i, 1] = float(words[5])
              vel[i, 2] = float(words[6])
          return pos, vel
docs: Read and return the next time frame