Modified Bollinger Bands

This script has been distributed for learning purposes.

A particular kind of price envelope is "Bollinger Bands" indicator. Upper and lower price range levels are determined by price envelopes. By default, Bollinger Bands are plotted in Tradingview as envelopes at a standard deviation level above and below the price's simple moving average (SMA). I attempted to modify the indicator in this version by adding several kinds of moving averages first. The key feature is that standard deviation should be modified. in Tradingview, SMA calculates the standard deviation. The allocated moving average should be used to calculate the std function when the base line is changed.