In our present codes, e.g., Zodiac, ODT, we choose \rho, T, and Y_i as the...
In our present codes, e.g., Zodiac, ODT, we choose \rho, T, and Y_i as the primitive variables. As a result, we want drho/dY_i=0 and drho/dT=0, and we do not want to use chain rule based on the tree to get drho/dY_i and drho/dT.