Matthew Knepley <[email protected]> writes:

Definitely debuggability.

Thanks.

It would be great if we automatically diagnose the failure of definiteness (I assume all these retain symmetry).

So long as a symmetric operator is input.

Maybe we are already doing this. Then we should improve the error message to give the user easy options for fixing it.

We only notice it at a higher level. The smoother could check whether its action is SPD with respect to each vector it is applied to at the cost of a dot product (check that x^T S x > 0). Actually, the problem is more subtle because if one wants an SPD multigrid cycle, they only need that the post-smoother is the transpose of the pre-smoother. This could also be checked, but I don't know how to do it without significant wasted work.