I have an expression involving subscripted variables, $x_i$ (and constants, $b_k,c_k,d_k$). I would like to compute the Jacobian but the most straightforward application of the D operator, $D[f,x[k]]$ always returns 0. I want to compute $\partial^2 f/\partial{x_i}\partial{x_j}$. Any help greatly appreciated. Thanks -- Len B
