[QiWang]

Dear SU2-ers,
I'm performing adjoint-based optimization for a last-step objective function (say, the -drag). I'm not sure whether the current framework is for time-averaged outputs or just the objective at the last time step. Where should I find that information and how can I make the objective function only at the last time step?

[bigfootedrockmidget]

Are you referring to this tutorial?


https://su2code.github.io/tutorials/..._Opt_NACA0012/


What do you want to change compared to this tutorial?

[QiWang]

Originally Posted by bigfootedrockmidget

Are you referring to this tutorial?


https://su2code.github.io/tutorials/..._Opt_NACA0012/


What do you want to change compared to this tutorial?

I want to perform optimization based on the last time step output only (say the last step drag)

One way I'm thinking about is to change the window function so that only the last time step has weight 1, and 0 for all other time steps.
In CWindowingTools.cpp there is a function

su2double CWindowingTools::GetWndWeight(WINDOW_FUNCTION windowId, unsigned long curTimeIter, unsigned long endTimeIter) {
  switch (windowId) {
    case WINDOW_FUNCTION::HANN:        return HannWindow(curTimeIter, endTimeIter);
    case WINDOW_FUNCTION::HANN_SQUARE: return HannSquaredWindow(curTimeIter, endTimeIter);
    case WINDOW_FUNCTION::BUMP:        return BumpWindow(curTimeIter, endTimeIter);
    case WINDOW_FUNCTION::SQUARE:      return 1.0;
  }
  return 1.0;
}

I could add a line

case WINDOW_FUNCTION::LAST_ONLY:   return (curTimeIter == endTimeIter) ? 1.0 : 0.0;

However, in the first step of adjoint (which correspond to the last step of the direct solver, curTimeIter is 0 while endTimeIter is nTimeIter). I'm confused about how the time indexing is done between direct and adjoint computations.

Another way is to change the averaging length.
In Cconfig.cpp, line 5337,

      if (Iter_Avg_Objective == 0.0) {
        Iter_Avg_Objective = nTimeIter;
      }

The default value of Iter_Avg_Objective is nTimeIter, and the objective function is averaged over the whole time domain.
I'm wondering whether changing this line to Iter_Avg_Objective = 1 would make the program perform optimization for objectives only at the last time step.
Of course this is a very dirty fix. I'm new to SU2 and having been learning for two weeks. I'm looking for professional users that could advise me with better options.

[bigfootedrockmidget]

One way I'm thinking about is to change the window function so that only the last time step has weight 1, and 0 for all other time steps.

How is this different from using a window with only one timestep or the averaging?
I still don't see how your setup differs from the tutorial, besides changing some numbers.