On Tue, 16 Jan 2018, David Knezevic wrote:
I'm working with Jonas on this topic, and I just wanted to add a few - The original issue that Jonas ran into was indeed due to a "constraint cycle".
Sorry my email crossed with yours!
- Our preferred fix is to detect constraint cycles and fix them ourselves, or at least to detect them and throw an error. What is the situation with error checking for constraint cycles at the moment?
I'm pretty sure there is none.
This seems dangerous to me since libMesh can currently silently give the wrong answer.
Agreed.
- If there is no error checking for constraint cycles, then I'd propose to add some optional error checking to DofMap
Certainly! Except that I'd make it mandatory in dbg+devel mode.
(and make sure this can be active in opt as well as dbg mode).
If that can be done sensibly, I suppose. However, a dbg+devel-mode-only check would be *easy* - dig into the function where we expand recursive constraints, and add a quick libmesh_assert() that each of the constrainer DoF indices doesn't equal the constrained DoF index at each step at the expansion. Doing that check in opt mode would be too expensive, even optionally, IMHO, since you'd be testing your do-we-do-testing flag a zillion times. If you make a separate function to test constraints for recursion before expanding them out, and only call that function after testing an optional flag, that would be fine in opt mode, but more repetitive to code.
I guess this is as simple as a function that is called after process_constraints that checks that all entries in constrain rows are unconstrained.
Hmm... because *if* the recursion terminated properly, then we'd expect that to be true after the expansion code was done? That might work. I wouldn't trust it, though. You're no longer proposing testing whether the constraints are expected to break after processing, you're proposing testing whether the processing looks broken in a specific way. It'll work for now, but then it may just fail to trigger after the next time we refactor process_constraints(). I suppose either way you'll want to add a unit test or two that catch cyclic constraints, and if we've got test coverage then I'm less worried about breaking things. So okay, this would be reasonable too. --- Roy ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
