code: def double_exponential_moving_average(data, period):
      
      catch_errors.check_for_period_error(data, period)
  
      dema = (2 * ema(data, period)) - ema(ema(data, period), period)
      return dema
docs: Double Exponential Moving Average.
  
      Formula:
      DEMA = 2*EMA - EMA(EMA)