= PDAF3_assimilate_global =

This page documents the routine `PDAF3_assimilate_global` of PDAF. The routine is part of the advanced [wiki:PDAF3_interface PDAF3 interface] that was introduced with PDAF V3.0.

The routine is used to execute the analysis step of all global ensemble filters (including the NETF and PF) and the local EnKF. The routine uses the functionalities provided by PDAF-OMI to yield a minimum number of arguments.

The routine is typically called in `assimilate_pdaf` or directly in the model code.

The general aspects of the filter specific routines `PDAF3_assimilate_*` are described on the page [ModifyModelforEnsembleIntegration Modification of the model code for the ensemble integration] and its sub-page on [InsertAnalysisStep inserting the analysis step]. 

The routine is used in both the fully-parallel and the flexible parallelization variants of the data assimilation system.

The interface for using the global filters is:
{{{
  SUBROUTINE PDAF3_assimilate_global(U_collect_state, U_distribute_state, &
                                 U_init_dim_obs_pdafomi, U_obs_op_pdafomi, &
                                 U_prepoststep, U_next_observation, status)
}}}
with the following arguments:
 * `U_collect_state`: [[BR]]The name of the user-supplied routine that initializes a state vector from the array holding the ensemble of model states from the model fields. This is basically the inverse operation to `U_distribute_state` used in `PDAF_get_state` as well as here. 
 * `U_distribute_state`:  [[BR]]The name of a user-supplied routine that initializes the model fields from the array holding the ensemble of model state vectors. This is the inverse operation to `U_collect_state`.
 * `U_init_dim_obs_pdafomi`: [[BR]]The name of the user-supplied routine that initializes the observation information and provides the size of observation vector. This routine is part of an OMI observation module. 
 * `U_obs_op_pdafomi`: [[BR]]The name of the user-supplied routine that acts as the observation operator on some state vector. This routine is part of an OMI observation module. 
 * `U_prepoststep`: [[BR]]The name of the user-supplied pre/poststep routine as in `PDAF_get_state`
 * `U_next_observation`: [[BR]]The name of a user supplied routine that initializes the variables `nsteps`, `timenow`, and `doexit`. The same routine is also used in `PDAF_get_state`.
 * `status`: [[BR]]The integer status flag. It is zero, if the routine is exited without errors.

**Note:**
 * The routine is identical to the routine `PDAFomi_assimilate_global` of PDAF 2. The new name reflects consistency with `PDAF3_assimilate_local`. If one has used `PDAFomi_assimilate_global` before one can just adapt the name of the called routine.
 * To use the localization in the LEnKF, one needs to call [wiki:PDAFomi_set_localize_covar] in the observation modules to initialize the localization information.
 * It is recommended that the value of `status_pdaf` is checked in the program after PDAFomi_assimilate_global is executed. Only if its value is 0 the initialization was successful.

The user-supplied call-back routines are described on the page on [ImplementAnalysisGlobal implementing the analysis step of the global filters].