[MITgcm-support] Nonlinear free surface and the adjoint

[gael forget]

Hi Christopher,
> I’m trying to do sensitivity studies using a nonlinear free surface. TAF gives warnings about extensive recomputations that disappear when I turn off the NLFS using #undef NONLIN_FRSURF in CPP_OPTIONS.
Activating NONLIN_FRSURF increases tape storage greatly but 
should not introduce extensive recomputations anymore.
> I’ve heard that ECCOv4 uses the NLFS in both forward and adjoint mode,
NLFS is indeed used in forward and adjoint for ECCO v4. 
> so either the recomputations are not that bad or there’s a way to make them go away. Does anyone know which is the case?
One thing to check is that DISABLE_SIGMA_CODE is defined.
If that is not the issue, I am not sure where the recomputation you get may come from.
> If neither, is there a flag I could set to use the NLFS for the forward integration but have it turned off in the adjoint?
Cheers,
Gael

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