code: def aroon_down(data, period):
      
      catch_errors.check_for_period_error(data, period)
      period = int(period)
  
      a_down = [((period -
              list(reversed(data[idx+1-period:idx+1])).index(np.min(data[idx+1-period:idx+1]))) /
              float(period)) * 100 for idx in range(period-1, len(data))]
      a_down = fill_for_noncomputable_vals(data, a_down)
      return a_down
docs: Aroon Down.
  
      Formula:
      AROONDWN = (((PERIOD) - (PERIODS SINCE PERIOD LOW)) / (PERIOD)) * 100