[MITgcm-devel] seaice dynamics: potential conflict of AB2 and adjoint

[Martin Losch]

Hi Patrick and other adjointers and adjointees,

this is just a "heads-up". 

When I implemented AB2 for the JFNK-solver, I made use of the global variables u/vIceNm1. They are (in case SEAICEuseAB2 = .TRUE.) read and written to the seaice_pickup - files. I now realized that when ALLOW_AUTODIFF_TAMC is defined, u/vIceNm1 are reset to zero in s/r seaice_model. Currently, JFNK and adjoint are exclusive, so that there is no problem, but if we ever consider using AB2 in the Picard/LSR solver (it's really easy to do), we have to keep this in mind.
(with AB2 the JFNK speeds up by 10-20%, maybe we would see something like that also for LSR)

Martin