= PDAF_assim_offline_enkf = 

This page documents the routine `PDAF_assim_offline_enkf` of PDAF. The routine was introduced with PDAF V3.0.

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 when using the EnKF is the following:
{{{
  SUBROUTINE PDAF_assim_offline_enkf(U_init_dim_obs, U_obs_op, &
                                 U_init_obs, U_prepoststep, U_add_obs_err, U_init_obscovar, status_pdaf)
}}}
with the following arguments:
 * `U_init_dim_obs`: The name of the user-supplied routine that provides the size of observation vector
 * `U_obs_op`: The name of the user-supplied routine that acts as the observation operator on some state vector
 * `U_init_obs`: The name of the user-supplied routine that initializes the vector of observations
 * `U_prepoststep`: The name of the pre/poststep routine as in `PDAF_get_state`
 * `U_add_obs_err`: The name of the user-supplied routine that adds the observation error covariance matrix to the ensemble covariance matrix projected onto the observation space.
 * `U_init_obscovar`: The name of the user-supplied routine that initializes the observation error covariance matrix.
 * `status_pdaf`: 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 [ImplementAnalysisenkf implementing the analysis step of the EnKF algorithm].

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