#2651: New warning message for missing boundary conditions

Reporter: Samuel Cupp Status: new Milestone: Version: Type: task Priority: minor Component: Carpet

Changes (by Samuel Cupp): I have made a pull request adding a warning inside ApplyPhysicalBCsForGroupI for when variables have no boundary conditions registered. Originally, there was a _cout_ statement only if a preprocessor flag was defined. I have found that this warning helped me discover several mistakes that would have been very difficult to track down without it. The associated pull request is [here](https://bitbucket.org/eschnett/carpet/pull-requests/53/carpet-added-warning-...).

For example, it made me realize that I never properly changed over BaikalVacuum’s BC selection to also register boundary conditions with the driver. If I had put this comment in earlier, my confusion about why the code was trying to sync+apply BCs way too often would have been instantly solved.

As another example, one function in BaikalVacuum reads one group everywhere and another interior. I had both everywhere, but the interior-only one has no BCs because it is only ever read on the interior. As such, I was triggering syncs for no reason. This warning pointed me to the real problem in my simulation very quickly, and this was causing my code to sync variables 24 (RK4 * variables in group) times more per iteration.

Finally, it led to me finding that MoL’s scheduling was trying to sync scalars (see [Ticket #2650](https://bitbucket.org/einsteintoolkit/tickets/issues/2650/fixing-write-state...). While not a performance issue like the above, this is incorrect behavior.

-- Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2651/new-warning-messag...