acf

         Compute the autocorrelation function of an evenly sample lightcurve

         time series analysis

         acf,time,rate,lag,acf,covf

         time      : the times at which the time series was measured
         rate      : the corresponding count rates

         none

         none

         lag       : sample time lags
         acf       : autocorrelation values to each time lag given in
                     a two-dimensional array, once without
                     correction-factor and once with.

         covf      : autocovariance values to each time lag given in
                     a one-dimensional array.

         none

         none

         evenly time series

         The autocorrelation function is computed according to the
         approximation of evenly sample given by
         covf(lag)=(1/(npt-lag))SUM_{j=1,..npt-lag}[x(j)-<x>][x(j+lag)-]
         acf(lag)=covf(lag)/covf(0)
         Additionally, a corection-factor given by Sutherland et
         al. 1978, Ajp 219, 1029P, is added.

         acf,time,rate,lag,acf,covf=covf

         Version 1.0, 1998.12.21, Sara Belloch IAAT, Joern Wilms IAAT.
                                 (benlloch@astro.uni-tuebingen.de)

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