Timo Heister

need a rebase after #4610

I will need to do some more research here, thank you @zjiaqi2018

> There are still a number of unaddressed comments. I am still working on addressing some of the issues and let you know once I think I am done. Sorry....

> but passing `invalid_unsigned_int` or `-1` is not much more descriptive than `false` Yes, but now you have two arguments that have to be consistent. > If you want to...

Yes, while not useful in most situations, I have at least one example where it helps: https://github.com/geodynamics/aspect/blob/d4f2d64b806809085cb1ae602f9b153a6ec1202f/tests/nullspace-freesurface-amg.prm#L1-L6

> (As it's a quarter shell with free slip top and bottom and periodic side boundaries, the net rotation would have to be removed.) Oh, interesting! I have not considered...

@naliboff FYI

Hi @naliboff, does that make sense to you?

@naliboff ?

@naliboff ?