Add a getter for grad P

[Sbte]

No description provided.

[Sbte]

@ipelupessy Please check if the last commit is what you need. The rest is some cleanup I thought I needed for gradp, but then decided that I may as well compute the vector itself on the fortran side instead.

[ipelupessy]

so ocean->getGradP('V') gets you a vector similar to state ith the gradPx and gradPy in 1st and second place (of 6)?

[Sbte]

Yes, or ocean->getGradP('C') if you want a copy. And Pz is also in there.

[ipelupessy]

I dunno if there is an easy way to do this, but as test I would try to fill up the state with linear ramps in both directions to see whether the resulting grads are constant...

[ipelupessy]

the estimate is checkerboard free?

[Sbte]

Yes, we discussed this at the meeting

[Sbte]

@ipelupessy The suggestion for that test was very useful. I added it and fixed the implementation accordingly.