Fractional derivatives

Last time we have seen that ARMA modelis can be integrated (and differentiated) to deal with non-stationarity present in the empirical data. ARIMA model should be sufficient in most cases, but if the empirical data is know to exhibit "true" long-range memory, then ordinary calculus will not work. In those cases one would have to use fractional calculus. Here we will take a brief look at fractional derivatives (and integrals).