We consider a vector of observables, not just one
Autoregressive (AR) model for a vector.
VAR(p) looks \(p\) back.
The AR(\(p\)) model is:
\(y_t=\alpha + \sum_{i=1}^p\beta y_{t-i}+\epsilon_t\)
VAR(\(p\)) generalises this to where \(y_t\) is a vector. We define VAR(\(p\)) as:
\(y_t\)
\(y_t=c + \sum_{i=1}^pA_i y_{t-i}+\epsilon_t\)
Include lagged y and lagged x (and current x)