code: def recenter(positions):
      '''Returns a list of new positions centered around the origin.
      '''
      (x0, y0, z0), (x1, y1, z1) = bounding_box(positions)
      dx = x1 - (x1 - x0) / 2.0
      dy = y1 - (y1 - y0) / 2.0
      dz = z1 - (z1 - z0) / 2.0
      result = []
      for x, y, z in positions:
          result.append((x - dx, y - dy, z - dz))
      return resulf recenter(positions):
      '''Returns a list of new positions centered around the origin.
      '''
      (x0, y0, z0), (x1, y1, z1) = bounding_box(positions)
      dx = x1 - (x1 - x0) / 2.0
      dy = y1 - (y1 - y0) / 2.0
      dz = z1 - (z1 - z0) / 2.0
      result = []
      for x, y, z in positions:
          result.append((x - dx, y - dy, z - dz))
      return result
docs: Returns a list of new positions centered around the origin.