Changed the registration of AD input variables in CDiscAdjFluidIteration

[thomasdick]

This is a small issue I noticed when I worked on some features for the discrete adjoint driver.
In CDiscAdjFluidIteration::RegisterInput the inputs for the AD tape are registered.
At the moment if kind_recording == RECORDING::SOLUTION_AND_MESH is set it only registers the flow variables and has no difference to RECORDING::SOLUTION_VARIABLES. If I understand the logic for this enum option correctly, it should register the flow variables and the mesh coordinates from geometry. I.e. if you want to add unctions to the driver, which can evaluate derivatives w.r.t. flow and geometry in one tape evaluation, you should use this option.

In addition, I change an out-of-date comment.

Proposed Changes

Register the geometry variables as inputs in the discrete adjoint flow iteration if 'kind_recording == RECORDING::SOLUTION_AND_MESH'.

PR Checklist

Put an X by all that apply. You can fill this out after submitting the PR. If you have any questions, don't hesitate to ask! We want to help. These are a guide for you to know what the reviewers will be looking for in your contribution.

• I am submitting my contribution to the develop branch.
• My contribution generates no new compiler warnings (try with the '-Wall -Wextra -Wno-unused-parameter -Wno-empty-body' compiler flags, or simply --warnlevel=2 when using meson).
• My contribution is commented and consistent with SU2 style.
• I have added a test case that demonstrates my contribution, if necessary.
• I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp) , if necessary.

[pcarruscag]

LGTM I don't think we are using that recording mode anywhere, might be a good candidate for removing / simplifying

[thomasdick]

I checked and I could not find a place in the code where this option is used explicitly. Since all the drivers split between primary recording for state variables and secondary recording for geometry variables for efficiency.

My own use case was for research I did, where I needed to record a tape w.r.t. to both. Since this is not ready to become a pull request any time soon, I do not really need this option.

If you suggest I can create a commit to remove the enum option for simplicity.

[pcarruscag]

If you plan to use it in the future let's keep it.