etmc
QUDA interface / QUDA-MG: study how the MG behaves when theta is changed
Currently, the QUDA interface does not track how the gauge field and MG setup are updated when the theta angles are changed in TBC calculations. This was never an issue before because different angles were done in different runs, but we now need to add facilities to the code to track changes of boundary conditions and update the fields accordingly. In the worst case scenario, the MG setup will have to be discarded and redone...
In the nissa-MG intergace I store a checksum of the configuration used for setup
https://github.com/sunpho84/nissa/blob/aef9815de954e01030aed42bcac784b23b0d285d/src/base/DDalphaAMG_bridge.cpp#L142
and then I compare each time the used configuration. If they differ, a new setup is issued. Maybe it's an overkill because with small angles the setup might work, but in general it's needed
Yes, for inversions I also thought of doing it this way but it doesn't generalise well to the HMC where updates are done less frequently and one has to have a notion of "distance between configurations". Ideally, in order not to complicate matters too much, I would of course like to use the same mechanism in the HMC as I do for simple inversions. I have to give it some thought.