def double_exponential_moving_average(data, period):
catch_errors.check_for_period_error(data, period)<EOL>dema = (<NUM_LIT:2> * ema(data, period)) - ema(ema(data, period), period)<EOL>return dema<EOL>
Double Exponential Moving Average.

Formula:
DEMA = 2*EMA - EMA(EMA)