[petsc-dev] VI vs. SNESLineSearchPostCheck and projecting to bounds

[Peter Brune]

 Seems to me we have at least two ways of enforcing physicality or other
constraints on the solution; SNESLineSearchPostCheck and the VI machinery.
I'm trying to solve PFLOTRAN examples that make extensive use of
SNESLineSearchPostCheck and am having to put postchecks at strategic places
in SNESNGMRES and other solvers that don't just use the line searches
directly make sure the solution becomes physical.

Jed, you've already complained about post-check checking the step after
taking it being nonsensical, and I agree on this point as well.  Should we
move towards an interface so that there's a general "SNESProjectToBounds"
or whatever, with VI doing what it needs to do through this as well? This
way we have the ability to solve the constrained problems with all the
solvers.  We already have hooks for this kind of thing in the DM.

Thanks,

- Peter
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