Hello, R people: I have a question in using fSeries package--the funciton garchFit and garchOxFit if adding a regression to the mean formula, how to estimate the model in R? using garchFit or garchOxFit? For example, Observations is {x,y}_t,there may be some relation between x and y. the model is y_t=gamma0 + *gamma1*x_t*+psi*e_{t-1}+e_t the gamma1*x_t is regression. e_t=sqrt(h_t)*N(0,1) h_t=alpha0+alpha1*e_t^2+beta*h_{t_1}~~~~~~~GARCH(1,1). I didn't know how to estimate the model using function garchFit or garchOxFit or other functions? because the argument in garchFit/garchOxFit is formular.mean=~arma(1,1). Do you have some instrucitons? thank you very much for you help. Best wishes Ma Yuchao [[alternative HTML version deleted]]