KINSOL: option to select QR orthogonalization strategy

[sebproell]

This option is available from SUNDIALS 6.0.0 onwards. If an older version is used, we throw an error if a user asks for an orthogonalization strategy different from the default.

[bangerth]

Nice! Just two minor textual issues.

Is it possible to clone one of the tests to check these features? It would be interesting to see how this affects the number of iterations.

[sebproell]

Thanks for the reviews! Regarding a test: the strategy only makes sense in a parallel setting and I first need to teach our N_Vector a few more efficient operations. The current state works, but technically we are not working on multi-vectors. I would write a test with all of these features on a larger example. The current FP iteration example just has three vector elements so there is not much too parallelize if I copy this one.

[bangerth]

That works, but it's worth pointing out that tests do not have to show useful use of features. Just the fact that they run through specific lines of code is often an important feature of a test.

[sebproell]

@bangerth Do you want me to change anything more here?

[kronbichler]

@bangerth can we merge this PR for now and add the test later? If I understand @sebproell correctly, he is going to work on modifications where the feature would be tested?

[sebproell]

Yes, I will continue working on this soon.

[bangerth]

I'd still like to have tests for this, but the code itself is ok.