def average_true_range(close_data, period):
tr = true_range(close_data, period)<EOL>atr = smoothed_moving_average(tr, period)<EOL>atr[<NUM_LIT:0>:period-<NUM_LIT:1>] = tr[<NUM_LIT:0>:period-<NUM_LIT:1>]<EOL>return atr<EOL>
Average True Range.

Formula:
ATRt = ATRt-1 * (n - 1) + TRt / n