[Amirkb]

Hi all,


I am trying to use the AD module in the discrete adjoint solver to calculate the sensitivity of the lift coefficient with respect to the closure coefficients of the SA turbulence model.


I've created new variable names in the CConfig class for the SA closure coefficients and have modified the code so that it reads the values for the coefficients from the config file, instead of the given hard coded values. (I would need to change the values later on).


Now I'm trying to get the sensitivity of my objective function (in this case Cl as specified in the config file) with respect to these closure coefficients.


I've modified the CDiscAdjSolver class in solver_structure.hpp and solver_structure.inl by adding new variables for the sensitivities I want to calculate, defining inline Get functions which return the sensitivity values, and defining virtual functions onto the CSolver class.


I've modified solver_adjoint_discrete.cpp by adding new variables which read in the values of the closure coefficients from the config class and passing these variables onto AD::RegisterInput() (these are done in the RegisterVariables routine), and then passing them onto SU2_TYPE::GetDerivative() to calculate the derivatives (this is done in the ExtractAdjoint_Variables routine). I store the derivative values as new variables called Total_Sens_SA, similar to what's already done for Total_Sens_AoA, for example.


The problem I have is that when I pass the variables onto SU2_TYPE::GetDerivative(), the output is returned as 0. As far as I see, I've followed the same steps that are done to get the other sensitivity values such as Total_Sens_AoA or Total_Sens_Mach, but I don't understand why the derivative is being returned as 0. Is there something I'm missing here? I assumed as long as I register the variables whose derivatives I want onto AD::RegisterInput() the rest should be taken care of inside the AD and codi modules and the derivatives should be calculated correctly?


Curiously, in output_structure.cpp where values such as Total_Sens_AoA are called again to be printed to screen, these values differ from those calculated inside solver_adjoint_discrete.cpp. This to me suggests that the sensitivity values are altered elsewhere, but I cannot seem to find where this occurs.


Any help would be appreciated.


Kind regards,
Amir

[pcg]

This question is being handled in https://github.com/su2code/SU2/issues/679

[Amirkb]

Question solved, see link above.