## 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: