Last edited [[Timestamp]]
= ''' Direct Model Changes ''' =

[[PageOutline]]

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Some modifications and additions are compulsory to integrate the Tangent and Adjoint Module to NEMO. They mainly consist in:
 * changing subroutines or parameters declaration from Private to Public for:
   * initialization
   * re-use
 * adding a subroutine to save the trajectory
 * adding parameters
 * updating namelist

== 1 - Non-Linear Trajectory ==
To evaluate the tangent and/or the adjoint at a time t, some actual parameters of the direct model are needed at the corresponding time t. To fulfill this purpose a subroutine, ''asm_trj_wri''  is added to write the trajectory. It is controlled with two logical parameters: ''lk_asminc'' and ''ln_trjwri''. The trajectory is saved with a certain saving frequency and only both logical parameter are set to TRUE.
Th

=== Subroutine: asm_trj_wri ===
A new subdirectory is created into /OPA/ named '''ASM'''. The file is '''asmtrj.F90'''.
The purpose of this routine is to write to file the model state trajectory for use with 4DVar. It is called in ''opa_model'' routine to save the initial state needed for the TAM and at the end of the ''stp'' routine.

Currently the following parameters are saved:
|| '''Parameters''' || '''Associated ccp keys''' ||
||emp ||   ||
||emps ||   ||
||un ||   ||
||vn ||   ||
||tn ||   ||
||sn ||   ||
||ta ||   ||
||sa ||   ||
||tb ||   ||
||sb ||   ||
||avmu ||   ||
||avmv ||   ||
||aeiu || lk_traldf_eiv  ||
||aeiv || lk_traldf_eiv  ||
||aeiw || lk_traldf_eiv  ||
||uslp || key_ldfslp  ||
||vslp || key_ldfslp  ||
||wslpi || key_ldfslp  ||
||wslpj || key_ldfslp  ||
||avs || key_zdfddm  ||
||strdmp || key_tradmp  ||
||hmlp || key_tradmp ||

''note: is it worth to add why (and where) there will be a need of these variables later in TAM?''

==== Specific management of the initial state ====
For the initial state of the model, some parameters need to be computed in ''asmtrj'' as they are not yet computed in opa.

''note: we still have zero value in emp/emps parameters. It needs to be solved quickly.''  

==== Linear Interpollation ====
For efficiency matters, the whole trajectory is of course not saved. Only a predefined steptime frequency is saved. The frequency ''nittrjfreq'' is controlled by namelist. The intermediate steptime will be estimated in TAM by linear interpollation.

==== Namelist ====
Parameters related to the model state saving is controlled by the namelist '''nam_asminc''' with:

 * ln_trjwri: Logical switch for writing out state trajectory
 * nittrjfrq: frequency of the trajectory used in 4D-VAR

== 2 - Routine modification ==

 * '''opa.F90''': 
   * include output trajectory fields (USE asmtrj and CALL asm_trj_wri)
 * '''step.F90''':
   * include output trajectory fields (CALL asm_trj_wri)
   * add temporary variables to save ta/sa (used as workspace in standard)

== 3 - Declaration Changes ==
The following table describes the change from PRIVATE to PUBLIC of some routines and parameters.

|| '''Modules''' || '''Routines''' || '''parameters''' ||
||dynadv || dyn_adv_ctl  || ||
||daymod || day_mth  || ||
||       ||          || sec1jan000 ||
||eosbn2 ||          || neos_init||
||sbcmod ||          || all from namelist namsbc||
||tradmp || cofdis, dtacof, dtacof_zoom  || ||
||  ||    ||strdmp, ttrdmp, resto ||
||traqsr ||    ||nksr, gdsr ||

 ''note: is it worth to add why (and where) there will be a need of these variables later in TAM?''