Auto regressive model

Hello everybody,

i have an EEG signal and am trying to use the auto regressive model on some channels of it.The problem am facing is calculaing the order of it.
the matlab fuctions am using:

NN=struc(na,nb,nk)
V = arxstruc(ze,zv,NN)
order=selstruc(V)
y=ar(ze,order)

my proble now is what are the values ze,zv,na,nb,nk and how do i calculate them?

thanks