Nonstationarity

[thepinkman]

I was looking for more clarity for what nonstationarity is. According to Schweser, “Nonstationarity means the covariance of the time series is not stationary.”
Fvckers. I actually paid for these notes! Can anyone elaborate a little?

 

[maratikus]

covariance stationary: constant mean, volatility, autocorrelations
autocorrelation(t,t-k) = autocorrelation(s,s-k)