Update model.py

        for t in range(self.T):

            '''

            Note: the following t denotes the index of x_t, not the t in the loop

            Note: the following t in the comments denotes the index of x_t, not the t in the loop

            When t = 1:

            # (1) d_1 ~ p(d_1|d_<1,x_=<1), Eq. (10) (sample d_1 based on reparameterization trick)

            # (2) h_1 = r(h_0, d_1, x_1), Eq. (3)