Barry Smith <[email protected]> writes:

Well, we did report the entire preconditioner was indefinite, but not what part of the preconditioner caused it to be indefinite.

Could run the smoother with CG for many steps and see if that reports indefiniteness. Would it, I’m not even sure of that.

I think it would report indefiniteness, but it depends on the RHS vector/initial guess.

We could easily add a test MatIsNonsingularM() i.e. a_ii > =0 a_ij <= 0, useful information but I don’t think it helps the user “fix” the problem.

If they actually have an M-matrix, everything should just work. So how to help them when they have a problem/formulation that produces a matrix where methods aren't working?