[MITgcm-devel] DIVA and seaice dynamics

[Patrick Heimbach]

Hi there,

I am trying to hunt down a problem with DIVA:
Running An’s ASTE setup with DIVA very quickly leads to diverging adjoint values.
After some unsuccessful fiddling with full ASTE setup, 
I went back to verification/global_ocean.cs32x15/
and constructed a DIVA setup based on input_ad.seaice/

I extended the run to 16 time steps (with nchklev_3 = 3, so it does 4 sweeps).
To my considerable amazement, astonishment, and surprise, it is the *DIVA*
that gives correct gradients, whereas the standard (non-DIVA) setup diverges 
(by many orders of magn.) after a couple of time steps.

(Ronaldo didn’t score 4 goals against Bayern today, so I think I got it right;
I actually ran twice to be sure).

When I switch seaice dynamics off, then non-DIVA and DIVA give good agreement.
For ASTE we’re switching off seaice dynamics in the adjoint, and that should
essentially happen in same/similar way with or without DIVA.
But apparently not so.

For the tests I’ve used:
      integer    nchklev_1
      parameter( nchklev_1      =  2 )
      integer    nchklev_2
      parameter( nchklev_2      =  3 )
      integer    nchklev_3
      parameter( nchklev_3      =  3 )
(I’ve also tested changing to nchklev_2 = 4).

Certainly, seaice dynamics shouldn’t play a big role in this verif.
so we expect gradients to be fairly similar with or without.
A vague hunch is that something gets messed up (in memory?)
that gets corrected due to adjoint dump/restart, but not
when running the adjoint in single sweep(???)

Ah, those divas… Any ideas, anyone?
-Patrick

---
Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
MIT | EAPS 54-1420 | 77 Massachusetts Ave | Cambridge MA 02139 USA
FON +1-617-253-5259 | FAX +1-617-253-4464 | SKYPE patrick.heimbach

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