code: def zmeshgrid(d):
      
      lin = xfun(2, d)
      one = ones(2, d)
  
      xx = zkronv(lin, one)
      yy = zkronv(one, lin)
  
      return xx, yy
docs: Returns a meshgrid like np.meshgrid but in z-order
      :param d: you'll get 4**d nodes in meshgrid
      :return: xx, yy in z-order