“…Assuming that m j has a multiplicative separability form in the time t and the covariate, the time varying linear model has been studied in [10,26,27,35,48,75,77] among others and the general multiplicative form has been recently studied in [12,34,70]. Moreover, when X j,i,n = Y i−j,n in (1.1), it becomes the nonparametric and nonlinear autoregressive process [60,Section 3.1]. Finally, we point out that (1.1) can be regarded as a discretized version of the Langevin equation…”