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Next: 3.19 Sensitivity of Air-Sea Up: 3.18 Global Ocean State Previous: 3.18.4 Compiling   Contents

3.18.5 Running the estimation

Copy the mitgcmuv_ad executable to input_ad/ and optim.x to the subdirectory input_ad/OPTIM/. Move into input_ad/. The first iteration is somewhat particular and is best done "by hand" while the following iterations can be run automatically (see below). Check that the iteration number is set to 0 in data.optim and run the MITgcm: 

% ./mitgcmuv_ad

The output files adxx_hfluxm.0000000000.* and xx_hfluxm.0000000000.* contain the sensitivity of the cost function to $ Q_\mathrm{netm}$ and the adjustment to $ Q_\mathrm{netm}$ (zero at the first iteration), respectively. Two other files called costhflux_tut_MITgcm.opt0000 and ctrlhflux_tut_MITgcm.opt0000 are also generated. They essentially contain the same information as the adxx_.hfluxm* and xx_hfluxm* files, but in a compressed format. These two files are the only ones involved in the communication between the adjoint model mitgcmuv_ad and the line-search algorithm optim.x. Only at the first iteration, are they both generated by mitgcmuv_ad. Subsenquently, costhflux_tut_MITgcm.opt$ n$ is an output of the adjoint model at iteration $ n$ and an input of the line-search. The latter returns an updated adjustment in ctrlhflux_tut_MITgcm.opt$ n+1$ to be used as an input of the adjoint model at iteration n+1.

At the first iteration, move costhflux_tut_MITgcm.opt0000 and ctrlhflux_tut_MITgcm.opt0000 to OPTIM/, move into this directory and link data.optim and data.ctrl locally: 

% cd OPTIM/
% ln -s ../data.optim .
% ln -s ../data.ctrl .
The target cost function fmin needs to be specified too: as a rule of thumb, it should be about 0.95-0.90 times the value of the cost function at the first iteration. This value is only used at the first iteration and does not need to be updated afterward. However, it implicitly specifies the ``pace'' at which the cost function is going down (if you are lucky and it does indeed diminish!). More in the ECCO section maybe ?

Once this is done, run the line-search algorithm: 

% ./optim.x
which computes the updated adjustment for iteration 1, ctrlhflux_tut_MITgcm.opt0001.

The following iterations can be executed automatically using the shell script cycsh found in input_ad/. This script will take care of changing the iteration numbers in the data.optim, launch the adjoint model, clean and store the outputs, move the costhflux* and ctrlhflux* files, and run the line-search algorithm. Edit cycsh to specify the prefix of the directories used to store the outputs and the maximum number of iteration.

next up previous contents
Next: 3.19 Sensitivity of Air-Sea Up: 3.18 Global Ocean State Previous: 3.18.4 Compiling   Contents
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