code: def split_grad_list(grad_list):
      
      g = []
      v = []
      for tower in grad_list:
          g.append([x[0] for x in tower])
          v.append([x[1] for x in tower])
      return g, v
docs: Args:
          grad_list: K x N x 2
  
      Returns:
          K x N: gradients
          K x N: variables