Warning! Frequently hits the execution time limit for scripts. Especially on initially adding to your chart. Often requires toggling show/hide indicator to get it to complete script execution within the time limit. YMMV!
From TASC Sept 2016 this is Ehler's Autocorrelation periodogram. A means of determining the dominant cycle ("ideal" indicator length / dynamic length).
As an example it's applied here to RSI or MFI. Lower indicator segment displays the autocorrelation spectrum and the computed dominant cycle. Upper segment is RSI/MFI.