Hello, Can anyone please help me with the spectral density function, Inversion formula, Spectral density function for ARMA(p,q) and Linear filters given on Page 41 of Tables? I cannot find their detail explanation in core reading. Also, how to find the number of cycles per unit time for given time series data set in R? So that I can use it for seasonal differencing I tries to use spectrum function on ldeaths data set in R and got the following output: I also used the spectrum function on EuStockMarkets FTSE data set and got the following output: Can anyone tell how to estimate no. of cycles per year on each of above dataset? What is the trick to understand above graphs?