def negative_directional_index(close_data, high_data, low_data, period):
catch_errors.check_for_input_len_diff(close_data, high_data, low_data)<EOL>ndi = (<NUM_LIT:100> *<EOL>smma(negative_directional_movement(high_data, low_data), period) /<EOL>atr(close_data, period)<EOL>)<EOL>return ndi<EOL>
Negative Directional Index (-DI).

Formula:
-DI = 100 * SMMA(-DM) / ATR