How can I write this in Divergence form

Question

Consider the PDE

$u_{xx}-(yu_y)_x-y(u_x)_y+yu_y+(y^2+\frac{1}{H^2(x)})u_{yy}$

I need to write this in divergence form. That is, I need to write it in the form

$\sum_{i,j}\frac{\partial}{\partial x_i}(a_{ij}\frac{\partial u}{\partial x_j})$

Any ideas?