The dispersion of volatility indices

The script is my implementation of "Forecasting a Volatility Tsunami" by Andrew Thrasher (Thrasher Analytics). You can find the paper here: researchgate.net/publication/317999480_Forecasting_a_Volatility_Tsunami
I've changed a bit the approach - instead of two volatility indices (VIX & VVIX), I used two more: VXN and VXD. Additionally, I average the percentiles, but there is an option to swtich it to the original approach.