[MITgcm-support] ECCO_CTRL_DEPRECATED code removal

[Martin Losch]

Dear ADlers,

The AD-related code is complicated with a lot of code for each control variable and cost function contribution, which is difficult to maintain. About 6 years ago, Gael Forget introduced a new and far more elegant way of defining control variables and cost function contributions in a generic way that is much easier to use and maintain (thanks Gael!). At this time, the “old” way is still available and can be turned on with the flag ECCO_CTRL_DEPRECATED (note however that the ECCO_CTRL_DEPRECATED code is not documented in the manual).

We are currently in the process of replacing all verification experiments that use this flag by identical versions without the flag. I.e. these experiment will be (nearly) the same as before, but will use the generic cost and control code, including the ones that use the ecco-pkg. Once this has happened, the “deprecated” code will naturally become non-functional very quickly because it is no longer tested. And then it will be time to remove it altogether, because, really, it is a pain to maintain. We will announce the time until removal (on the order of months), once all verification experiments are converted (soon).

For the AD-user this means that from a certain point on (marked by a checkpoint), it will not be possible to update the code without getting rid of all code within ECCO_CTRL_DEPRECATED ifdefs. Previous MITgcm checkpoints will continue to work, and easily accessible, because we are all git-wizards, aren’t we? You just cannot do a simple update to have access to potentially new features (it will still be possible however to merge versions at your own risk, depending on your git-savy).

Let us know if you are still using the ECCO_CTRL_DEPRECATED code, and we will try to accommodate any specific requests to help smooth this transition.

Regards,
Martin and the MITgcm devel team
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