code: def negative_directional_index(close_data, high_data, low_data, period):
      
      catch_errors.check_for_input_len_diff(close_data, high_data, low_data)
      ndi = (100 *
             smma(negative_directional_movement(high_data, low_data), period) /
             atr(close_data, period)
             )
      return ndi
docs: Negative Directional Index (-DI).
  
      Formula:
      -DI = 100 * SMMA(-DM) / ATR