[Gretl-users] Deterministic terms in VEC models

Dear fellow gretl users, I have two questions about deterministic trends in VEC models. gretl offers the five traditional approaches to VEC modelling, either omitting all deterministic terms or including constants and trends in restricted and unrestricted combinations. I was wondering if there are any good "rules of thumb" for when to choose which approach? The EViews manual, for example, suggests choosing a model with constant + restricted trend if some of the level variables appear to oscillate around a linear trend, I believe (although my memory may serve me wrong here). Also, from the gretl manual I learned that the specification of a VEC model with a constant and *restricted* trend looks like this (LaTeX code): $\Delta y_{t}=\mu_{0}+\mu_{1}t+\alpha\beta'y_{t-1}+ \sum_{i=1}^{p-1}\Gamma_{i}\Delta y_{t-i}+\epsilon_{t}$ where $\alpha'\perp\mu_{1}=0$ I was wondering how the restriction of alpha being orthogonal to mu is achieved in practice? Thanks in advance for your help! Stefan