I have an ARCH model like this: Delta y = y_{t+1} - t_t = k (theta - y_t) Delta t + v_t N(0,1) sqrt(Delta t) where v_t^2 = a_0 + a_1 (y_{t-1} - E[y_{t-1}])^2 Is there any R function that, given a series y_i, determines k, theta, a_0 and a_1 by maximum likelihood? I tried to use garch from tseries, but didn't understant how the output from its summary relate to the above quantities. Alberto Monteiro