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The ALFF and PerAF of a simulated time series (X1), and its derivative time series of multiplying A by 2 (X2) and by 3 (X3). ALFF and PerAF were calculated for each time series. ALFF value is proportional to the mean value of the time series, but PerAF keeps the same. X and y axis are time and intensity, respectively, in arbitrary unit.
