def aroon_down(data, period):
catch_errors.check_for_period_error(data, period)<EOL>period = int(period)<EOL>a_down = [((period -<EOL>list(reversed(data[idx+<NUM_LIT:1>-period:idx+<NUM_LIT:1>])).index(np.min(data[idx+<NUM_LIT:1>-period:idx+<NUM_LIT:1>]))) /<EOL>float(period)) * <NUM_LIT:100> for idx in range(period-<NUM_LIT:1>, len(data))]<EOL>a_down = fill_for_noncomputable_vals(data, a_down)<EOL>return a_down<EOL>
Aroon Down.

Formula:
AROONDWN = (((PERIOD) - (PERIODS SINCE PERIOD LOW)) / (PERIOD)) * 100