15.2 Time-varying seasonality and amplitude

If $\beta_1$ and $\beta_2$ vary in time then the seasonal cycle also varies in time. Let’s imagine that $\beta_1$ varies from -1 to 1 over our 100 time steps while $\beta_2$ varies from 1 to -1.

So the seasonal cycle flips between the start and end of our time series.

A time series simulated with that flip looks like so: