Output Gap in Romania and Bulgaria (Hodrick-Prescott Filter)

In this post I use Hodrick-Prescott filter (a very simple, widely used but also controversial filter) to estimate the output gap of Bulgaria and Romania during the period Q1 2000 - Q1 2017. The output gap is estimated in Eviews, but I also attach Excel step-by-step implementation for Bulgaria (https://drive.google.com/file/d/0B5OoJUuowhtZMzZLMlBBb1JhOTQ/view?usp=sharing)

I attach the pdf-file with theoretical part. https://drive.google.com/file/d/0B5OoJUuowhtZaDBZdWRLem9ZbHM/view?usp=sharing