= PDAF_assimilate_ensrf = 

This page documents the routine `PDAF_assimilate_ensrf` of PDAF. The routine is used to execute the ENSRF/EAKF filters, which was added to PDAF with version 3.0. 

The routine is typically called in `assimilate_pdaf` or directly in the model code. However, for newer implementations we recommend to use the generic routine [wiki:PDAF3_assimilate_local] since less user-supplied call-back routines are required with the PDAF3 interface. 

The general aspects of the filter specific routines `PDAF_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 the fully-parallel implementation variant of the data assimilation system and can also be used for the flexible parallelization variant. 

The interface for the ENSRF/EAKF is the following:
{{{
SUBROUTINE PDAF_assimilate_ensrf(U_collect_state, U_distribute_state, &
     U_init_dim_obs, U_obs_op, U_init_obs, U_init_obsvars, &
     U_localize_covar_serial, &
     U_prepoststep, U_next_observation, outflag)
}}}
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 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`: [[BR]]The name of the user-supplied routine that provides the size of the observation vector
 * `U_obs_op`: [[BR]]The name of the user-supplied routine that acts as the observation operator on some state vector
 * `U_init_obs`: [[BR]]The name of the user-supplied routine that initializes the vector of observations
 * `U_init_obsvars`: [[BR]]The name of the user-supplied routine that initializes the vector of observation error variances.
 * `U_localize_covar_serial`: [[BR]]The name of the user-supplied routine that applies the covariance localization for a single observation
 * `U_prepoststep`: [[BR]]The name of the user-supplied pre/poststep routine as in `PDAF_get_state`
 * `U_next_observation`: [[BR]]The name of the user-supplied routine that initializes the variables `nsteps`, `timenow`, and `doexit`. The same routine is also used in `PDAF_get_state`.
 * `status_pdaf`: [[BR]]The integer status flag. It is zero, if the routine is exited without errors. 


The user-supplied call-back routines are described on the page on [wiki:ImplementAnalysisENSRF_EAKF implementing the analysis step of the ENSRF/EAKF]. Here also the possible choices of `subtype` are explained. These select the particular filter variant.

It is recommended to check value of `status_pdaf` in the program after PDAF_assimilate_enkf is executed. Only if its value is 0 the initialization was successful.