What are the applications of complex numbers in modern economics? I wonder what the most interesting applications of imaginary numbers in mainstream economics are. I read about the unit root test (Dickey-Fuller test) in time-series analysis; and I studied System Dynamics about phase portraits that were determined by complex numbers. So maybe the maths of these numbers are necessary for econometrics and for more sophisticated macroeconomic modelling. 

To sum up, what are the most important application of complex numbers in economics? Could you give me some examples, models relevant to complex numbers?

I will be grateful if you can send me this information.
You might refer to this answer to a question similar to yours.

Financial economics often use the complex plane to visualize duration and the internal rate of return, to which this resource proves very helpful.