code: def index2bool(index, length=None):
      
      if index.shape[0] == 0 and length is None:
          return np.arange(0, dtype = bool)
      if length is None: length = index.max()+1
          
      sol = np.zeros(length, dtype=bool)
      sol[index] = True
      return sol
docs: Returns a numpy boolean array with Trues in the input index 
      positions.
      
      :param index: index array with the Trues positions.
      :type index: ndarray (type=int)
      :param length: Length of the returned array.
      :type length: int or None
      :returns: array with Trues in the input index positions.
      :rtype: ndarray    
      
      .. seealso:: :func:`bool2index`