This is the Laguerre Relative Strength Index (RSI) Indicator described in Chapter 14.  Ehlers shows that you can apply the Laguerre Filter to familiar indicators.

PriceIn = defaults to Close, which is correct for this indicator, unlike others in the book

Gamma = defaults to 0.5 as described in the book (Ehlers notes that you can adjust this damping factor to best suit your own data)

For more information on this indicator, refer to Chapter 14 of "Cybernetic Analysis for Stocks and Futures" by John Ehlers, Publisher: John Wiley & Sons; (March 19, 2004), ISBN: 0471463078