old_contents: from __future__ import absolute_import
  
  import numpy as np
  
  def add_params(p1, p2):
      res = []
      for x,y in zip(p1,p2):
          res.append(x+y)
      return res
  
  def get_neutral(array):
      res = []
      for x in array:
          res.append(np.zeros_like(x))
      return res
  
  def divide_by(array_list, num_workers):
      for i in xrange(len(array_list)):
          array_list[i] /= num_workers
      return array_list
  
new_contents: from __future__ import absolute_import
  
  import numpy as np
  
  def add_params(p1, p2):
      res = []
      for x,y in zip(p1,p2):
          res.append(x+y)
      return res
  
  def subtract_params(p1, p2):
      res = []
      for x,y in zip(p1,p2):
          res.append(x-y)
      return res
  
  def get_neutral(array):
      res = []
      for x in array:
          res.append(np.zeros_like(x))
      return res
  
  def divide_by(array_list, num_workers):
      for i in xrange(len(array_list)):
          array_list[i] /= num_workers
      return array_list
  
subject: Subtract two sets of parameters