A while back I decided to look up some of the more academic methods and models used to conduct analysis on financial time series data. I saw the progression in linear statistical tools going from correlation, to ARMA, to ARIMA, and then to GARCH---and then found out implied volatility is probably as effective as GARCH at its best. It all seemed a lot of work for very little when there are shortcuts available that can do the trick for far less mental expenditure. Still I took note of nonlinear methods being discussed as the next frontier but didn't really look into it. My question now is what does it mean when one talks of nonlinear trading analysis? Is this principally about neural networks? Something else? What? Thank you for any explanation that you give.