Autocorrelation at lag 9. Included for completion and consistency.
ac_9(y, acfv = stats::acf(y, 9, plot = FALSE, na.action = na.pass))
the input time series
vector of autocorrelation, if exist, used to avoid repeated computation.
autocorrelation at lag 9
B.D. Fulcher and N.S. Jones. hctsa: A computational framework for automated time-series phenotyping using massive feature extraction. Cell Systems 5, 527 (2017).
B.D. Fulcher, M.A. Little, N.S. Jones Highly comparative time-series analysis: the empirical structure of time series and their methods. J. Roy. Soc. Interface 10, 83 (2013).