This function implements the filtering algorithm of Lunde and Timmermann (2004) to identify Bull and Bear states
run_filtering_alg(index)vector containing the stock price index
A logical vector that contains TRUE for Bull states and FALSE for Bear states
Lunde, A. and Timmermann, A. (2004). Duration Dependence in Stock Prices: An Analysis of Bull and Bear Markets. Journal of Business and Economic Statistics, 22 (3), 253-273.