= PDAF_assim_offline_etkf = 

This page documents the routine `PDAF_assim_offline_etkf` of PDAF. 

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 ETKF is the following:
{{{
  SUBROUTINE PDAF_assim_offline_etkf(U_init_dim_obs, U_obs_op, &
                                 U_init_obs, U_prepoststep, U_prodRinvA, U_init_obsvar, 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_prodRinvA`: The name of the user-supplied routine that computes the product of the inverse of the observation error covariance matrix with some matrix provided to the routine by PDAF. This operation occurs during the analysis step of the SEIK filter.
 * `U_init_obsvar`: The name of the user-supplied routine that provides a mean observation error variance to PDAF (This routine will only be executed, if an adaptive forgetting factor is used)
 * `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 [ImplementAnalysisetkf implementing the analysis step of the ETKF algorithm].

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