What are the applications of AR and MA model? To put my question exactly, when to use AR model and when to use MA model(for example, like when it is seasonal or when there is a trend, etc). In other words, which model to chose if it is seasonal, if it has trend, if both seasonal and trend, and if no trend and not seasonal? It will be good if someone explains that with an example.
auto.arima() can be used to find the parameters of AR and MA easily in R. But I happen to find lower AIC values when using different parameters other than parameters found by
auto.arima(). Which parameters is better to use? If parameters with lower AIC value is only better, then how to find those parameters without trying manually all possible parameters?