= PDAF3_assim_offline_lenkf =

This page documents the routine `PDAF3_assim_offline_lenkf` of PDAF. The routine is part of the advanced PDAF3 interface that was introduced with PDAF V3.0. 

|| **Note:** This routine exists for backward-compatibility for the LEnKF with PDAF V2.3, in particular for existing implementations using `localize_covar_pdafomi`. We recommend to use the new PDAF3 interface using [wiki:PDAF3_put_state_global] that avoids the need to implement the additional call-back routine `localize_covar_pdafomi`. ||

The routine is used for the offline coupled mode of PDAF, which is described on the page: [wiki:OfflineImplementationGuide Implementation Guide for Offline Coupling].

The interface is:
{{{
  SUBROUTINE PDAF3_assim_offline_lenkf(U_init_dim_obs_pdafomi, U_obs_op_pdafomi, &
                                 U_localize_covar_pdafomi, U_prepoststep, &
                                 status)
}}}

with the following arguments:
 * `U_init_dim_obs_pdafomi`: The name of the user-supplied routine that initializes the observation information and provides the size of observation vector
 * `U_obs_op_pdafomi`: The name of the user-supplied routine that acts as the observation operator on some state vector
 * `U_localize_covar_pdafomi`: The name of the user-supplied routine that Applies covariance localization to the matrices HP and HPH^T^
 * `U_prepoststep`: The name of the user-supplied pre/poststep routine as in `PDAF_get_state` (Note that the place of `U_prepoststep` has changed compared to the previous routine `PDAFomi_assimilate_lenkf`)
 * `status`: The integer status flag. It is zero, if the routine is exited without errors. 


For the EnKF, the user-supplied routines are essentially executed in the order they are listed in the interface to PDAFomi_put_state_lenkf. 

The user-supplied call-back routines are described on the page on [ImplementAnalysislenkf implementing the analysis step of the local EnKF].

It is recommended that the value of `status_pdaf` is checked in the program after PDAFomi_put_state_lenkf is executed. Only if its value is 0 the initialization was successful.