I need to solve a mathematical operation that is shown in the figure attached below. I am simulating an adjoint field and I wanna compute the product between a derivative of the base flow velocity and the aerodynamic force of the adjoint field, at the wall boundary. I know that in the FilterAeroforces.cpp, the forces are computed in each element, then an integral is applied. So I would like to know how  I can take the derivative of the base flow in these elements by reading the baseflow.fld. If someone can help me, I thank you. 

Daiane I. Dolci.