code: def calc_one_vert_inverse(one_vert, xyz=None, exponent=None):
      
      trans = empty(xyz.shape[0])
      for i, one_xyz in enumerate(xyz):
          trans[i] = 1 / (norm(one_vert - one_xyz) ** exponent)
      return trans
docs: Calculate how many electrodes influence one vertex, using the inverse
      function.
  
      Parameters
      ----------
      one_vert : ndarray
          vector of xyz position of a vertex
      xyz : ndarray
          nChan X 3 with the position of all the channels
      exponent : int
          inverse law (1-> direct inverse, 2-> inverse square, 3-> inverse cube)
  
      Returns
      -------
      ndarray
          one vector with values for one vertex